This review tries to present an overview of the most important parameters to be taken in
consideration in the evaluation of interferometer biosensors. Waveguide interferometers have particular
importance, because by utilizing the combination of two very sensitive methods, the waveguiding and the
interferometry techniques, they offer very good reliability and possibility for miniaturization and integration in
optical chips. By using the evanescent wave technology they measure the interaction between receptors and
biomolecules in real time without using labels. Receptors are immobilized onto a sensor surface and the
interaction with the biomolecules near it cause a refractive index change. A large number of applications in life
sciences, including binding kinetics of receptor-biomolecule pairs and virus-protein interactions, are using
evanescent wave-based biosensors for their studies. This article describes the technology behind their sensing
techniques, and a range of applications where they are used.
The establishment of sensor systems has elated recompenses such as measurement in flammable and explosive atmospheres, resistance to electrical noises, trimness, geometrical suppleness, measurement of slight sample volumes, remote sensing in unreachable sites or harsh atmospheres and multi-sensing. Biosensors are logical devices composed of a recognition component of biological origin and a physico-chemical transducer. Immobilization plays a foremost character in developing the biosensor by incorporating both the above mentioned mechanisms. In this paper, the real world applications pertaining the analysis of fiber optic sensors and biosensors for environmental and clinical monitoring have been reviewed.
Monitoring of concrete structures by electro mechanical impedance technique IEI GSC
By Dr. S.N.Khante Associate Professor & Bhagyashri Sangai
at 31st National Convention of Civil Engineers
organised by
Gujarat State Center, The Institution of Engineers (India) at Ahmedabad
This document describes a new open-source Python application called PAME (Plasmonic Assay Modeling Environment) for modeling plasmonic biosensors. PAME combines aspects of material modeling, thin-film design, fiber optics, and spectroscopy into an intuitive graphical interface. It allows users to design complex nanomaterials, simulate the response of sensors to changes in the local environment, and provide new insights into experimental observations. Example simulations using PAME model the response of a fiber optic refractometer coated with gold nanoparticles to increasing concentrations of glycerin, and simulate protein binding to a sensor with a mixed layer of gold and silver nanoparticles.
Application of non destructive test for structural health monitoring - state ...eSAT Journals
Abstract
The concept of non-destructive testing (NDT) is to obtain material properties “in place” specimens without the destruction of the specimens and to do the structural health monitoring. NDT using Rebound hammer, Ultra pulse velocity, Half-cell potential, core cutter, carbonation depth, rebar locator, Rapid chloride penetration test, electric resistivity meter test and vibration base analysis by data analoger are very popular and highly effective in conducting structural health monitoring. The structure can be investigated by using a visual inspection, NDT, laboratory and field test performance. In this article a review of these tests have been provided to conduct effective structural health monitoring of a RCC structure
Keywords: Non-destructive test, visual inspection, corrosion, compressive strength
The Namur Nanosafety Centre at the University of Namur provides physicochemical characterization, toxicity assessment, and training services for nanomaterials. Their areas of expertise include nanomaterial characterization, studies of nanomaterial fate and biodistribution, in vitro and in vivo toxicity testing following OECD guidelines, and regulation. They have equipment for characterization, toxicity assessment, and have conducted projects in quality control of nanomaterials, hazard identification, and regulatory testing. They offer customized services and training to companies to support safe development and use of nanomaterials.
Nanoparticles show promise for biomedical imaging and diagnosis due to their large size and multifunctionality compared to small molecules. Magnetic iron oxide nanoparticles are commonly used in MRI because they shorten T2 relaxation times, allowing hydrogen protons to move closer to the magnet and produce clearer images. Various types of functionalized magnetic nanoparticles including amine, carboxyl, epoxy and IDA functionalized nanoparticles are used for applications like immunoassay, gene transfection, biomolecule separation, cell separation, enzyme immobilization, drug delivery, and biomedical imaging. Nanoparticles also show potential for targeted cancer drug delivery and simultaneous imaging and therapy.
Nanobiomaterials are very effective components for several biomedical and pharmaceutical studies. Among the metallic, organic, ceramic and polymeric nanomaterials, metallic nanomaterials have shown certain prominent biomedical applications. Enormous works have been done to synthesize, analyse and administer the metallic nanoparticles for various kinds of medical and therapeutic applications, during the last forty years. In these analyses, the prominent biomedical applications of ten metallic nanobiomaterials have been reviewed from various sources and works. It has been found that almost nine of them are used in a very wide spectrum of medical and theranostic applications.
This document discusses the properties and potential applications of graphene. It begins by listing graphene's superlative physical properties such as its strength, flexibility, conductivity and impermeability. It then outlines some potential applications of graphene such as ultra-fast internet, quick phone charging, and use in bionic devices. The document discusses different production methods for graphene and its derivatives. It provides an overview of the National Graphene Institute and Graphene Engineering Innovation Centre in the UK and their roles in developing graphene applications and commercialization through collaboration with industry partners. In closing, it notes the wide range of potential applications of graphene across various sectors.
The establishment of sensor systems has elated recompenses such as measurement in flammable and explosive atmospheres, resistance to electrical noises, trimness, geometrical suppleness, measurement of slight sample volumes, remote sensing in unreachable sites or harsh atmospheres and multi-sensing. Biosensors are logical devices composed of a recognition component of biological origin and a physico-chemical transducer. Immobilization plays a foremost character in developing the biosensor by incorporating both the above mentioned mechanisms. In this paper, the real world applications pertaining the analysis of fiber optic sensors and biosensors for environmental and clinical monitoring have been reviewed.
Monitoring of concrete structures by electro mechanical impedance technique IEI GSC
By Dr. S.N.Khante Associate Professor & Bhagyashri Sangai
at 31st National Convention of Civil Engineers
organised by
Gujarat State Center, The Institution of Engineers (India) at Ahmedabad
This document describes a new open-source Python application called PAME (Plasmonic Assay Modeling Environment) for modeling plasmonic biosensors. PAME combines aspects of material modeling, thin-film design, fiber optics, and spectroscopy into an intuitive graphical interface. It allows users to design complex nanomaterials, simulate the response of sensors to changes in the local environment, and provide new insights into experimental observations. Example simulations using PAME model the response of a fiber optic refractometer coated with gold nanoparticles to increasing concentrations of glycerin, and simulate protein binding to a sensor with a mixed layer of gold and silver nanoparticles.
Application of non destructive test for structural health monitoring - state ...eSAT Journals
Abstract
The concept of non-destructive testing (NDT) is to obtain material properties “in place” specimens without the destruction of the specimens and to do the structural health monitoring. NDT using Rebound hammer, Ultra pulse velocity, Half-cell potential, core cutter, carbonation depth, rebar locator, Rapid chloride penetration test, electric resistivity meter test and vibration base analysis by data analoger are very popular and highly effective in conducting structural health monitoring. The structure can be investigated by using a visual inspection, NDT, laboratory and field test performance. In this article a review of these tests have been provided to conduct effective structural health monitoring of a RCC structure
Keywords: Non-destructive test, visual inspection, corrosion, compressive strength
The Namur Nanosafety Centre at the University of Namur provides physicochemical characterization, toxicity assessment, and training services for nanomaterials. Their areas of expertise include nanomaterial characterization, studies of nanomaterial fate and biodistribution, in vitro and in vivo toxicity testing following OECD guidelines, and regulation. They have equipment for characterization, toxicity assessment, and have conducted projects in quality control of nanomaterials, hazard identification, and regulatory testing. They offer customized services and training to companies to support safe development and use of nanomaterials.
Nanoparticles show promise for biomedical imaging and diagnosis due to their large size and multifunctionality compared to small molecules. Magnetic iron oxide nanoparticles are commonly used in MRI because they shorten T2 relaxation times, allowing hydrogen protons to move closer to the magnet and produce clearer images. Various types of functionalized magnetic nanoparticles including amine, carboxyl, epoxy and IDA functionalized nanoparticles are used for applications like immunoassay, gene transfection, biomolecule separation, cell separation, enzyme immobilization, drug delivery, and biomedical imaging. Nanoparticles also show potential for targeted cancer drug delivery and simultaneous imaging and therapy.
Nanobiomaterials are very effective components for several biomedical and pharmaceutical studies. Among the metallic, organic, ceramic and polymeric nanomaterials, metallic nanomaterials have shown certain prominent biomedical applications. Enormous works have been done to synthesize, analyse and administer the metallic nanoparticles for various kinds of medical and therapeutic applications, during the last forty years. In these analyses, the prominent biomedical applications of ten metallic nanobiomaterials have been reviewed from various sources and works. It has been found that almost nine of them are used in a very wide spectrum of medical and theranostic applications.
This document discusses the properties and potential applications of graphene. It begins by listing graphene's superlative physical properties such as its strength, flexibility, conductivity and impermeability. It then outlines some potential applications of graphene such as ultra-fast internet, quick phone charging, and use in bionic devices. The document discusses different production methods for graphene and its derivatives. It provides an overview of the National Graphene Institute and Graphene Engineering Innovation Centre in the UK and their roles in developing graphene applications and commercialization through collaboration with industry partners. In closing, it notes the wide range of potential applications of graphene across various sectors.
Use of nanotechnology in medical science (pros and cons)Vikram Kataria
here in this presentation I had shared the basic information regarding use of nanotechnology in medical science and what wonders and improvements that nano technology did in the field of medical science.
The document is a presentation on writing scientific papers. It discusses the structure and components of an introduction section. An effective introduction (1) presents the research field and importance, (2) identifies gaps, questions or limitations in current understanding, and (3) discusses the state of the art in recent research findings to provide context for the study. The purpose is to establish why the present study is important and timely.
Optical waveguide sensors that use evanescent wave interactions have attracted significant attention from researchers. Such sensors offer advantages for chemical sensing applications, including miniaturization potential, the ability to discriminate surface and bulk effects, suitability for measuring highly absorbing and scattering media due to short effective path lengths, enabling of full or quasi-distributed sensing to measure analyte concentration profiles over distances, and providing designers control over interaction parameters. Evanescent wave fiber optic sensors also offer economic benefits due to the availability of light emitting diodes and sensitive photodetectors.
Nanomaterials in biomedical applicationsumeet sharma
This document discusses nanomaterials and their biomedical applications. It begins by defining nanomaterials as objects with at least one dimension between 1-100 nanometers. It then classifies nanomaterials and discusses some common terms like nanoshells and quantum dots. The document focuses on the biomedical applications of nanomaterials, including biological imaging using quantum dots, targeted drug delivery using nanoparticles, and cancer treatment using magnetic nanoparticles. In summary, the document outlines different types of nanomaterials, their properties, and various ways they can be used for biomedical purposes such as imaging and targeted drug delivery.
In the past few decades a large amount of attention has been given to health
service’s technology. Advances in electronic components, computer technology, and images processing have contributed considerably to the expansion and improvement of the field. However, there is evidence that several other related topics still need to be explored, such as X-ray imaging in the routine mass screening for medical diagnosis.
Tumors formation is one of the most common human health problems and large
efforts have been undertaken world wide to tackle the disease. Breast cancer specifically seems to affect a large percentage of the female population. Research indicates that breast cancer treatment is most effective if the disease is diagnosed in its early stages of development. Traditionally, X-ray technologies have been used for breast screening film mammography and its success in detecting breast cancer has been reconfirmed throughout the past few decades. However, the technique has several limitations, and further improvements are required if we wish to achieve early stage diagnosis. Image formation in radiological diagnosis is the result of the complex
interdependence of many factor. Creating an ideal balance among them could improve the image to such a degree that it could be used in a clinical setting, where the minimum radiation dose would be applied to the patient. The factors which increase radiation dose and affect image quality can be grouped as: radiation quality, photon intensity, Xray detection sensitivity, and reduction of background through scattered radiation. Optimum performance is dependent on the improvement of the assessments of these phenomena. In the past, standard methods of quality control have been introduced which have lead to a partial improvement in the image evaluation techniques. Some methods, widely applied, involve the use of test objects or phantoms for the establishment of comparison parameters. However, the methods that use phantoms, are frequently not
as reliable as radiation based diagnoses of asymptomatic woman produce. In addition,the subjective nature of image interpretation by medical professionals can make the assessment process very difficult. Consequently, the currently available tools which are
used for breast clinical image formation and interpretation regularly results in an incorrect diagnosis.
In past years, the commercially introduced digital detectors for mammography
were seen as an important advancement since they provided both a higher acquisition speed and a lower associated radiation dose. However, up until this point, the quality of the produced images is comparable to the images obtained with film detectors.
....
This document discusses nanotechnology and electron beam technology for producing nanoparticles. It summarizes that electron beam technology can be used to evaporate materials to produce nanoparticles through vacuum evaporation. This technique is versatile, efficient and cost-effective for producing metallic and non-metallic nanoparticles. The document also discusses how nanoparticles of silver, silica and nanocomposites have been produced and studied for their antimicrobial properties and ability to decrease toxicity of drugs like antituberculosis medications.
Rapid Characterization of Multiple Regions of Interest in a Sample Using Auto...PerkinElmer, Inc.
IR microscopy is a well-established analytical technique for the measurement and identification of small samples down to a few micrometers in size. It is used extensively in the polymer, pharmaceutical, chemical, food, and electronics industries, to name a few, often identifying small contaminations or foreign objects of unknown origin. In forensic applications small particles of materials such as drugs, paint chips, residues or fibers are often collected as evidence and analyzed by IR microscopy. The type and size of the material, as well as the matrix in which the sample is contained, will dictate the
type of IR microscopy sampling technique to be deployed; transmission, reflectance, or ATR. The Spotlight™ 200i IR microscope is a fully automated system comprising:
• Automated X, Y, Z stage
• Automatic illxumination LEDs
• Autofocus
• Auto correction
• Automated switching between transmission and reflectance
• Automated dropdown ATR crystal
All of these features are controlled using the Spectrum 10 software.
Nanomedicine is an emerging field that uses nanotechnology for medical applications such as diagnosis, treatment, and disease prevention. It involves engineering materials and devices at the nanoscale of 1 to 100 nanometers to exploit their unique properties. This allows for innovations like controlled drug delivery, molecular imaging, and biosensing. Some key technologies involved include nanoparticles, quantum dots, carbon nanotubes, dendrimers, and liposomes. Potential applications range from molecular imaging and cancer theranostics to drug delivery, gene therapy, and tissue engineering. Nanomedicine offers opportunities for earlier disease diagnosis and more effective, safer, and personalized treatment approaches.
The document summarizes a conference on microfluidics technologies being held on October 20-21, 2015 in London. The conference will bring together experts working in microfluidic development and applications for medical research. Over two days, talks will examine strategies and technologies in microfluidics, and feature case studies on using microfluidics in areas like point-of-care diagnostics, single cell analysis, and organ-on-a-chip applications. Confirmed speakers include professors from universities in Europe and the US. The conference aims to provide a forum for networking and exploring how microfluidics can progress medical research and patient care.
This document describes how laser-induced breakdown spectroscopy (LIBS) was used to generate 3D elemental images of nanoparticle distribution in biological tissue at multiple scales. Sliced kidney tissue sections were mapped using LIBS to reconstruct the global nanoparticle distribution throughout the entire organ. Higher resolution LIBS imaging was also performed on specific regions of interest by repeatedly ablating the same tissue volume. This proof-of-concept study demonstrates that LIBS can quantitatively image both endogenous and exogenous elements in 3D within entire organs.
Electro-physiological characterisation of cells for healthcare applicationsajayhakkumar
This document summarizes Dr. Soumen Das' talk on electro-physiological characterization of cells for healthcare applications. The talk discusses how micro- and nanotechnologies are enabling the manipulation and analysis of biological systems at the cellular scale. This includes techniques such as soft lithography, microfluidics, and dielectrophoresis that allow label-free separation and analysis of cells. The scaling effects between microscale devices and biology enables more sensitive detection. These techniques have applications in personalized healthcare such as cancer detection by analyzing changes in non-biological properties of cells.
It has been almost decades since the “war on cancer” was declared. It is now generally
believed that personalized medicine is the future for cancer patient management.
Possessing unprecedented potential for early detection, accurate diagnosis, and
personalized treatment of cancer, nanoparticles have been extensively studied over the last
decade. In this report, I will try to summarize the current state-of-the-art nanoparticles in
biomedical applications targeting cancer. Multi- functionality nanoparticle-based agents.
Targeting ligands, imaging labels, therapeutic Drugs, and other. And the Role of Chemical
Engineers in this field and the promise that it holds for future.
These slides use concepts from my (Jeff Funk) course entitled analyzing hi-tech opportunities to show how the cost and performance of micro-fluidics are improving. Miro-fluidic devices have small micro-channels that analyze many types of fluidics. They can be fabricated from many materials including paper, textiles, and plastics. Plastics are the most recent to emerge and their fabrication relies on many of the same techniques that are used to fabricate integrated circuits. This means that they have been experiencing very rapid improvements as fabrication techniques are improved for ICs and then used to make micro-fluidic MEMS. (micro-mechanical electrical systems). Micro-fluidics are widely used in health care to analyze bacteria in water, glucose in sweat, nitrate contamination in water, and the blood of mosquitoes. Emerging applications include analysis of blood for early cancer detection.
The Seventh Annual BEACON Symposium and Technology fair bionanotechologyBokani Mtengi
This document provides an agenda for The Seventh Annual BEACON Symposium and Technology Fair on Bionanotechnology: The World of Small in Medicine, including a list of speakers from academic, corporate and medical institutions who will discuss advances in bionanotechnology, as well as sponsors, exhibitors, and abstracts of the speaker presentations.
Mason - Modelling radiation damage in cellular systemsAva Roberts
This project will develop a model for simulating radiation damage in cellular systems using MBN Explorer software. The model will study interactions between radiation (X-rays or ions) and biological components (DNA, proteins, etc.) to identify which biomolecular bonds are most susceptible to damage. In collaboration with other PhD students, the model may then explore how different radiosensitizers induce bond breaks, leading to cell death and improved radiotherapy. The student will spend time training with MBN Explorer in Frankfurt and will have opportunities to collaborate across physics, chemistry, biology, medicine, and business on radiation damage topics.
This document summarizes applications of nanotechnology in biomedical systems for diagnostics and therapy. It discusses how nanoparticles can be used for targeted drug delivery and theranostics (combining therapy and diagnosis). Examples discussed include using microcantilevers and atomic force microscopy to detect small mass differences for applications like screening enzyme inhibitors, and using noble metal nanoparticles for label-free detection of biomarkers. The significance of understanding nanomaterials to develop safe and effective clinical tools is also noted.
This document summarizes recent applications of nanoparticles in biology and medicine. It discusses how nanoparticles can be used as fluorescent biological labels, for drug and gene delivery, and for detecting pathogens and proteins. Nanoparticles are a suitable size for biological tagging because they are comparable in size to proteins. The core nanoparticle is often coated with biocompatible materials and attached to biological coatings like antibodies. Recent applications discussed include using nanoparticles to stimulate bone growth for tissue engineering and destroying tumors through localized heating with nanoparticles.
Plasmonic wave assessment via optomechatronics system for biosensor applicationIJECEIAES
Transduction biosensor (mass-based, optical and electrochemical) involves analysis, recognition and amplification in the acquired sample. In this work, the plasmonic-based biosensor was employed without using tags. It is crucial to determine angles of Brewster (Ɵb) and critical (Ɵc) for generating plasmonic resonance (Ɵr). The objective is to verify a cost-effective plasmonic biosensor through Fresnel simulation and experimentation of a developed optomechatronics system. The borosilicate glass, Au and Air layers were simulated with the Winspall 3.02 simulator. The optomechatronics system consists of: 1-optics (650 nm laser, slit, polarizer, photodiode), 2-mechanical (bipolar stepper motors, gears, stages) and 3-electronics (PIC18F4550, liquid crystal display (LCD) and drivers). Later, the software performs angular interrogation by reading the reflected beam from a rotating prism at 0.1125. Experimentation to simulation accuracy indicates that percentage differences for Ɵr and Ɵc are 1% and 0.2%, respectively. In conclusion, excellence verification was successfully achieved between experimentation and simulation. It proved that the lowcost optomechatronics system is capable and reliable to be deployed for the biosensor application.
Nano-fiber Diameters as Liquid Concentration SensorsRadhi Chyad
The document discusses using nano-fiber diameters as liquid concentration sensors. Specifically, it examines using nano-fibers to sense the concentration of D-glucose solutions and measure the refractive index. It describes how nano-fibers act as sensors by etching the cladding with HF solution. Experiments were conducted using nano-fibers and light transmission to measure the concentration of sugar solutions. Results showed the peak transmission decreased with increasing sugar concentration, indicating nano-fibers can successfully be used as liquid concentration sensors.
biosensor, modern, principles, technology, applications, working of sensor, types of sensor , nanomaterial, based biosensor(nanosensor) optical biosensor, flourescent biosensor, electrochemical and glucose biosensor, genetically encoded biosensor, microbial biosensor, cancer , references included, advantages and disadvantages also included.
1) Biosensors are devices that use biological or chemical reactions to measure analytes by generating signals proportional to analyte concentration. They are used in applications like disease monitoring, drug discovery, and pollution detection.
2) A biosensor consists of a bioreceptor that recognizes the analyte, a transducer that converts the biorecognition into a measurable signal, electronics that process the signal, and a display that shows the results.
3) Important characteristics of biosensors include selectivity for the target analyte, reproducibility of results, stability over time and varying conditions, high sensitivity to detect low analyte levels, and a linear response over different analyte concentrations.
Use of nanotechnology in medical science (pros and cons)Vikram Kataria
here in this presentation I had shared the basic information regarding use of nanotechnology in medical science and what wonders and improvements that nano technology did in the field of medical science.
The document is a presentation on writing scientific papers. It discusses the structure and components of an introduction section. An effective introduction (1) presents the research field and importance, (2) identifies gaps, questions or limitations in current understanding, and (3) discusses the state of the art in recent research findings to provide context for the study. The purpose is to establish why the present study is important and timely.
Optical waveguide sensors that use evanescent wave interactions have attracted significant attention from researchers. Such sensors offer advantages for chemical sensing applications, including miniaturization potential, the ability to discriminate surface and bulk effects, suitability for measuring highly absorbing and scattering media due to short effective path lengths, enabling of full or quasi-distributed sensing to measure analyte concentration profiles over distances, and providing designers control over interaction parameters. Evanescent wave fiber optic sensors also offer economic benefits due to the availability of light emitting diodes and sensitive photodetectors.
Nanomaterials in biomedical applicationsumeet sharma
This document discusses nanomaterials and their biomedical applications. It begins by defining nanomaterials as objects with at least one dimension between 1-100 nanometers. It then classifies nanomaterials and discusses some common terms like nanoshells and quantum dots. The document focuses on the biomedical applications of nanomaterials, including biological imaging using quantum dots, targeted drug delivery using nanoparticles, and cancer treatment using magnetic nanoparticles. In summary, the document outlines different types of nanomaterials, their properties, and various ways they can be used for biomedical purposes such as imaging and targeted drug delivery.
In the past few decades a large amount of attention has been given to health
service’s technology. Advances in electronic components, computer technology, and images processing have contributed considerably to the expansion and improvement of the field. However, there is evidence that several other related topics still need to be explored, such as X-ray imaging in the routine mass screening for medical diagnosis.
Tumors formation is one of the most common human health problems and large
efforts have been undertaken world wide to tackle the disease. Breast cancer specifically seems to affect a large percentage of the female population. Research indicates that breast cancer treatment is most effective if the disease is diagnosed in its early stages of development. Traditionally, X-ray technologies have been used for breast screening film mammography and its success in detecting breast cancer has been reconfirmed throughout the past few decades. However, the technique has several limitations, and further improvements are required if we wish to achieve early stage diagnosis. Image formation in radiological diagnosis is the result of the complex
interdependence of many factor. Creating an ideal balance among them could improve the image to such a degree that it could be used in a clinical setting, where the minimum radiation dose would be applied to the patient. The factors which increase radiation dose and affect image quality can be grouped as: radiation quality, photon intensity, Xray detection sensitivity, and reduction of background through scattered radiation. Optimum performance is dependent on the improvement of the assessments of these phenomena. In the past, standard methods of quality control have been introduced which have lead to a partial improvement in the image evaluation techniques. Some methods, widely applied, involve the use of test objects or phantoms for the establishment of comparison parameters. However, the methods that use phantoms, are frequently not
as reliable as radiation based diagnoses of asymptomatic woman produce. In addition,the subjective nature of image interpretation by medical professionals can make the assessment process very difficult. Consequently, the currently available tools which are
used for breast clinical image formation and interpretation regularly results in an incorrect diagnosis.
In past years, the commercially introduced digital detectors for mammography
were seen as an important advancement since they provided both a higher acquisition speed and a lower associated radiation dose. However, up until this point, the quality of the produced images is comparable to the images obtained with film detectors.
....
This document discusses nanotechnology and electron beam technology for producing nanoparticles. It summarizes that electron beam technology can be used to evaporate materials to produce nanoparticles through vacuum evaporation. This technique is versatile, efficient and cost-effective for producing metallic and non-metallic nanoparticles. The document also discusses how nanoparticles of silver, silica and nanocomposites have been produced and studied for their antimicrobial properties and ability to decrease toxicity of drugs like antituberculosis medications.
Rapid Characterization of Multiple Regions of Interest in a Sample Using Auto...PerkinElmer, Inc.
IR microscopy is a well-established analytical technique for the measurement and identification of small samples down to a few micrometers in size. It is used extensively in the polymer, pharmaceutical, chemical, food, and electronics industries, to name a few, often identifying small contaminations or foreign objects of unknown origin. In forensic applications small particles of materials such as drugs, paint chips, residues or fibers are often collected as evidence and analyzed by IR microscopy. The type and size of the material, as well as the matrix in which the sample is contained, will dictate the
type of IR microscopy sampling technique to be deployed; transmission, reflectance, or ATR. The Spotlight™ 200i IR microscope is a fully automated system comprising:
• Automated X, Y, Z stage
• Automatic illxumination LEDs
• Autofocus
• Auto correction
• Automated switching between transmission and reflectance
• Automated dropdown ATR crystal
All of these features are controlled using the Spectrum 10 software.
Nanomedicine is an emerging field that uses nanotechnology for medical applications such as diagnosis, treatment, and disease prevention. It involves engineering materials and devices at the nanoscale of 1 to 100 nanometers to exploit their unique properties. This allows for innovations like controlled drug delivery, molecular imaging, and biosensing. Some key technologies involved include nanoparticles, quantum dots, carbon nanotubes, dendrimers, and liposomes. Potential applications range from molecular imaging and cancer theranostics to drug delivery, gene therapy, and tissue engineering. Nanomedicine offers opportunities for earlier disease diagnosis and more effective, safer, and personalized treatment approaches.
The document summarizes a conference on microfluidics technologies being held on October 20-21, 2015 in London. The conference will bring together experts working in microfluidic development and applications for medical research. Over two days, talks will examine strategies and technologies in microfluidics, and feature case studies on using microfluidics in areas like point-of-care diagnostics, single cell analysis, and organ-on-a-chip applications. Confirmed speakers include professors from universities in Europe and the US. The conference aims to provide a forum for networking and exploring how microfluidics can progress medical research and patient care.
This document describes how laser-induced breakdown spectroscopy (LIBS) was used to generate 3D elemental images of nanoparticle distribution in biological tissue at multiple scales. Sliced kidney tissue sections were mapped using LIBS to reconstruct the global nanoparticle distribution throughout the entire organ. Higher resolution LIBS imaging was also performed on specific regions of interest by repeatedly ablating the same tissue volume. This proof-of-concept study demonstrates that LIBS can quantitatively image both endogenous and exogenous elements in 3D within entire organs.
Electro-physiological characterisation of cells for healthcare applicationsajayhakkumar
This document summarizes Dr. Soumen Das' talk on electro-physiological characterization of cells for healthcare applications. The talk discusses how micro- and nanotechnologies are enabling the manipulation and analysis of biological systems at the cellular scale. This includes techniques such as soft lithography, microfluidics, and dielectrophoresis that allow label-free separation and analysis of cells. The scaling effects between microscale devices and biology enables more sensitive detection. These techniques have applications in personalized healthcare such as cancer detection by analyzing changes in non-biological properties of cells.
It has been almost decades since the “war on cancer” was declared. It is now generally
believed that personalized medicine is the future for cancer patient management.
Possessing unprecedented potential for early detection, accurate diagnosis, and
personalized treatment of cancer, nanoparticles have been extensively studied over the last
decade. In this report, I will try to summarize the current state-of-the-art nanoparticles in
biomedical applications targeting cancer. Multi- functionality nanoparticle-based agents.
Targeting ligands, imaging labels, therapeutic Drugs, and other. And the Role of Chemical
Engineers in this field and the promise that it holds for future.
These slides use concepts from my (Jeff Funk) course entitled analyzing hi-tech opportunities to show how the cost and performance of micro-fluidics are improving. Miro-fluidic devices have small micro-channels that analyze many types of fluidics. They can be fabricated from many materials including paper, textiles, and plastics. Plastics are the most recent to emerge and their fabrication relies on many of the same techniques that are used to fabricate integrated circuits. This means that they have been experiencing very rapid improvements as fabrication techniques are improved for ICs and then used to make micro-fluidic MEMS. (micro-mechanical electrical systems). Micro-fluidics are widely used in health care to analyze bacteria in water, glucose in sweat, nitrate contamination in water, and the blood of mosquitoes. Emerging applications include analysis of blood for early cancer detection.
The Seventh Annual BEACON Symposium and Technology fair bionanotechologyBokani Mtengi
This document provides an agenda for The Seventh Annual BEACON Symposium and Technology Fair on Bionanotechnology: The World of Small in Medicine, including a list of speakers from academic, corporate and medical institutions who will discuss advances in bionanotechnology, as well as sponsors, exhibitors, and abstracts of the speaker presentations.
Mason - Modelling radiation damage in cellular systemsAva Roberts
This project will develop a model for simulating radiation damage in cellular systems using MBN Explorer software. The model will study interactions between radiation (X-rays or ions) and biological components (DNA, proteins, etc.) to identify which biomolecular bonds are most susceptible to damage. In collaboration with other PhD students, the model may then explore how different radiosensitizers induce bond breaks, leading to cell death and improved radiotherapy. The student will spend time training with MBN Explorer in Frankfurt and will have opportunities to collaborate across physics, chemistry, biology, medicine, and business on radiation damage topics.
This document summarizes applications of nanotechnology in biomedical systems for diagnostics and therapy. It discusses how nanoparticles can be used for targeted drug delivery and theranostics (combining therapy and diagnosis). Examples discussed include using microcantilevers and atomic force microscopy to detect small mass differences for applications like screening enzyme inhibitors, and using noble metal nanoparticles for label-free detection of biomarkers. The significance of understanding nanomaterials to develop safe and effective clinical tools is also noted.
This document summarizes recent applications of nanoparticles in biology and medicine. It discusses how nanoparticles can be used as fluorescent biological labels, for drug and gene delivery, and for detecting pathogens and proteins. Nanoparticles are a suitable size for biological tagging because they are comparable in size to proteins. The core nanoparticle is often coated with biocompatible materials and attached to biological coatings like antibodies. Recent applications discussed include using nanoparticles to stimulate bone growth for tissue engineering and destroying tumors through localized heating with nanoparticles.
Plasmonic wave assessment via optomechatronics system for biosensor applicationIJECEIAES
Transduction biosensor (mass-based, optical and electrochemical) involves analysis, recognition and amplification in the acquired sample. In this work, the plasmonic-based biosensor was employed without using tags. It is crucial to determine angles of Brewster (Ɵb) and critical (Ɵc) for generating plasmonic resonance (Ɵr). The objective is to verify a cost-effective plasmonic biosensor through Fresnel simulation and experimentation of a developed optomechatronics system. The borosilicate glass, Au and Air layers were simulated with the Winspall 3.02 simulator. The optomechatronics system consists of: 1-optics (650 nm laser, slit, polarizer, photodiode), 2-mechanical (bipolar stepper motors, gears, stages) and 3-electronics (PIC18F4550, liquid crystal display (LCD) and drivers). Later, the software performs angular interrogation by reading the reflected beam from a rotating prism at 0.1125. Experimentation to simulation accuracy indicates that percentage differences for Ɵr and Ɵc are 1% and 0.2%, respectively. In conclusion, excellence verification was successfully achieved between experimentation and simulation. It proved that the lowcost optomechatronics system is capable and reliable to be deployed for the biosensor application.
Nano-fiber Diameters as Liquid Concentration SensorsRadhi Chyad
The document discusses using nano-fiber diameters as liquid concentration sensors. Specifically, it examines using nano-fibers to sense the concentration of D-glucose solutions and measure the refractive index. It describes how nano-fibers act as sensors by etching the cladding with HF solution. Experiments were conducted using nano-fibers and light transmission to measure the concentration of sugar solutions. Results showed the peak transmission decreased with increasing sugar concentration, indicating nano-fibers can successfully be used as liquid concentration sensors.
biosensor, modern, principles, technology, applications, working of sensor, types of sensor , nanomaterial, based biosensor(nanosensor) optical biosensor, flourescent biosensor, electrochemical and glucose biosensor, genetically encoded biosensor, microbial biosensor, cancer , references included, advantages and disadvantages also included.
1) Biosensors are devices that use biological or chemical reactions to measure analytes by generating signals proportional to analyte concentration. They are used in applications like disease monitoring, drug discovery, and pollution detection.
2) A biosensor consists of a bioreceptor that recognizes the analyte, a transducer that converts the biorecognition into a measurable signal, electronics that process the signal, and a display that shows the results.
3) Important characteristics of biosensors include selectivity for the target analyte, reproducibility of results, stability over time and varying conditions, high sensitivity to detect low analyte levels, and a linear response over different analyte concentrations.
20101114 An intracellular glucose biosensor based on nanoflake ZnOAlim Polat
This document describes the development of an intracellular glucose biosensor based on nanoflake zinc oxide (ZnO). Glucose oxidase was immobilized on nanoflake ZnO grown on the tip of a glass capillary. The sensor showed a fast response time of 4 seconds and a logarithmic response to glucose concentrations between 500 nM to 10 mM. Measurements in human adipocytes and frog oocytes matched reported intracellular glucose levels. The sensor monitored increased intracellular glucose from insulin stimulation. Nanoflake ZnO provided higher sensitivity than previous ZnO nanorod-based sensors due to its larger surface area. The simple fabrication and good performance in sensitivity, stability, selectivity and reproducibility demonstrate nanoflake ZnO is a promising material for reliable intracellular glucose
Chemistry Of Reverse Micelle Based CoatingsBeth Salazar
This document discusses fiber optic biosensors and their advantages over traditional detection methods. Fiber optic biosensors can detect biological materials without requiring labeling, making the process faster and less toxic. They have excellent light permeability and are easy and inexpensive to manufacture. Fiber optic biosensors can illuminate the target with light and transmit the detected light back through the fiber. While promising, fiber optic biosensors still have limitations to overcome for widespread clinical use.
Peak Level Advancement of Sensors and its Applications.JagadishM25
1. The document is a project report submitted by 5 students to the Department of Chemistry on peak level advancement of sensors and its applications.
2. It discusses the working principles of reference electrodes and sensors, drawbacks of current sensors and solutions, and new sensor technologies like surface plasmon resonance biosensors for early cancer detection.
3. Surface plasmon resonance biosensors allow for label-free detection of molecular binding events using plasmon resonance and have advantages of being cost-effective, portable, easy to operate, and non-hazardous compared to other techniques.
This document discusses nanotechnology and its applications in medicine. It begins with the origins and definitions of nanotechnology. Some key approaches to nanofabrication include top-down and bottom-up methods. Nanocarriers such as liposomes, dendrimers, micelles, and nanoparticles can be used for targeted drug delivery. Nanotechnology has applications in regenerative medicine, disease diagnosis using nanomolecular diagnostics, and in-vitro diagnostics including nano biosensors and nanoarrays. Overall, nanomedicine holds promise for earlier disease detection and more targeted treatment approaches.
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JBEI Research Highlights - August 2017 Irina Silva
This document summarizes a new software tool called Rhorix that interfaces quantum chemical topology (QCT) calculations with the 3D graphics program Blender. Rhorix allows chemists to visually represent molecular structures and atoms-in-molecules using electron density from QCT calculations. This mapping provides a parameter-free means of understanding chemical phenomena based directly on quantum mechanical principles. The software will help chemists and artists visually represent chemical phenomena relevant to bioenergy through modern 3D drawing tools.
This document discusses the use of Chemical Force Microscopy (CFM) and functionalized nanomechanical cantilever sensors (NCS) and microcantilever-based biosensors (MC-B) for nano/biosensor applications. CFM helps organize molecules on sensor surfaces in a well-defined structure to make the sensors more reproducible and sensitive. NCS and MC-B can detect very small forces and mass changes using the deflection or vibration frequency of microcantilevers. CFM is useful for characterizing sensor surfaces on the nanoscale, studying chemical interactions, and optimizing molecular adsorption to improve sensor performance. Key parameters like tip quality and surface cleaning/functionalization must be controlled to obtain reliable data
This document discusses the development of nanotechnology-enabled chemical sensors and biosensors. It provides examples of applications that would benefit from portable, low-cost sensors, such as point-of-care medicine and environmental monitoring. The document outlines various nanomaterials and technologies being used to create miniaturized, sensitive sensors, including the use of carbon nanotubes, metal oxides, and transistors to detect chemicals and biomolecules. It also discusses potential applications for disease surveillance and bioterrorism prevention.
Optical waveguide sensors that use evanescent wave interactions have attracted significant attention from researchers. Such sensors offer advantages for chemical sensing applications, including miniaturization potential, discrimination of surface and bulk effects, suitability for absorbing and scattering media due to short effective path length, enabling of full or quasi-distributed sensing over considerable distances, and control over interaction parameters and response time. Evanescent wave fiber optic sensors also provide economic benefits due to the ability to use light emitting diodes and photodetectors.
Sk microfluidics and lab on-a-chip-ch5stanislas547
This document discusses Lab-on-a-Chip (LOC) technology and its applications in biomedical fields. LOC systems integrate full laboratory functions onto a single microchip to handle extremely small fluid volumes. Key points:
- LOCs deal with fluid transport and analysis on the microscale and are a type of microfluidic device. They can perform complex analyses like DNA separation and detection.
- LOC research grew in the 1990s as groups developed micropumps and sensors to integrate fluid processing. Genomics and military applications further drove research.
- LOCs have advantages like low sample/reagent use, fast analysis, compact size, and potential for point-of-care medical diagnostics. Examples include
This document discusses developments in photon-counting detectors for single-molecule fluorescence microscopy. It describes two common optical configurations used: point-like excitation and detection of freely diffusing molecules, and wide field illumination and detection of surface-immobilized molecules. Each approach currently uses different optimal detectors, but there is room for improvement. Recent developments aim to increase the throughput of single-molecule fluorescence spectroscopy using parallel arrays of single-photon avalanche diodes, and develop large-area photon-counting cameras for fluorescence lifetime imaging at the single-molecule level with sub-nanosecond resolution.
Noninvasive blood glucose monitoring system based on near-infrared method IJECEIAES
This document summarizes a study that developed a non-invasive blood glucose monitoring system using near-infrared spectroscopy. The system uses a finger sensor with an LED light source to collect photoplethysmography signals from the finger, which are preprocessed with an analog circuit and filtered with a Butterworth filter. A linear regression model is used to correlate the photoplethysmography peak data to blood glucose concentration measurements, developing individual calibration models for each of the 10 subjects. Experimental results found a root mean square error of 8.264-13.166 mg/dL between predicted and measured glucose values, with an R-squared value of 0.839, demonstrating clinically acceptable prediction in the standard error grid.
This document discusses several characterization techniques for nanoparticles, including UV-Visible spectroscopy, dynamic light scattering, zetasizing, transmission electron microscopy, and scanning electron microscopy. UV-Visible spectroscopy can be used to quantitatively determine concentrations of absorbers. Dynamic light scattering measures particle size based on Brownian motion. Zetasizing measures particle size, zeta potential, and molecular weight. Transmission electron microscopy produces high-resolution 2D images using electrons. Scanning electron microscopy produces 3D images using focused electron beams. These techniques provide information on particle structure, shape, size, and composition.
This document evaluates the biocompatibility of materials commonly used in microelectromechanical systems (MEMS) for implantable medical devices. Six MEMS materials (silicon, silicon dioxide, silicon nitride, silicon carbide, gold, and titanium) and one encapsulating material were fabricated using standard MEMS processes and sterilized. All materials were tested using the ISO 10993 biocompatibility standards, which assess cytotoxicity, sensitization, irritation, and other effects. Scanning electron microscopy was also used to examine the materials before and after sterilization. The results indicated few biocompatibility concerns for using these materials in implants, though further testing may still be required to satisfy all regulatory requirements.
This document summarizes research using a radio frequency sensor to detect and distinguish particle concentration. The RF sensor uses changes in dielectric permittivity to detect particles without labelling. Test results showed the sensor could detect 4 μm polystyrene particles at different concentrations and frequencies, and distinguish between 1% and 10% concentrations. Future work will further test the sensor's ability to detect different particles and concentrations at more frequencies to support its use in applications like medicine, biology and environmental monitoring.
This document discusses topics that will be covered in a course on nanobiosensors, including the history and applications of biosensors, principles of molecular recognition and signal transduction, sources and design of biological recognition elements, modeling of reactions for various biosensor applications, modification of sensor surfaces and immobilization techniques, detection methods and physical sensors, fabrication of biosensors, and data acquisition and analysis. Examples of commercial biosensors and recent developments in new-generation nano-engineered biosensors are also mentioned.
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s
−1
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Positive interaction: mutualism, proto-cooperation, commensalism
Negative interaction: Ammensalism (antagonism), parasitism, predation, competition
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Mutualistic relationship between organisms allows them to act as a single organism.
Examples of mutualism:
i. Lichens:
Lichens are excellent example of mutualism.
They are the association of specific fungi and certain genus of algae. In lichen, fungal partner is called mycobiont and algal partner is called
II. Syntrophism:
It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism.
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Compound A
Utilized by population 1
Compound B
Utilized by population 2
Compound C
utilized by both Population 1+2
Products
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Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria.
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ii. Lactobacillus arobinosus and Enterococcus faecalis:
In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are able to grow together but not alone.
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We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
Interferometric Evanescent Wave Biosensor Principles and Parameters
1. IOSR Journal of Applied Physics (IOSR-JAP)
e-ISSN: 2278-4861.Volume 7, Issue 6 Ver. I (Nov. - Dec. 2015), PP 84-96
www.iosrjournals
DOI: 10.9790/4861-07618496 www.iosrjournals.org 84 | Page
Interferometric Evanescent Wave Biosensor Principles and
Parameters
Moisi Xhoxhi1
, Alma Dudia2
, Aurel Ymeti3
1
Department of Engineering Physics, Faculty of Engineering Mathematics and Engineering Physics,
Polytechnic University of Tirana, Street "Muhamet Gjollesha", Tirana, Albania
2, 3
Nanoalmyona BV, Heutinkstraat 463, 7535 AZ Enschede, The Netherlands
Abstract: This review tries to present an overview of the most important parameters to be taken in
consideration in the evaluation of interferometer biosensors. Waveguide interferometers have particular
importance, because by utilizing the combination of two very sensitive methods, the waveguiding and the
interferometry techniques, they offer very good reliability and possibility for miniaturization and integration in
optical chips. By using the evanescent wave technology they measure the interaction between receptors and
biomolecules in real time without using labels. Receptors are immobilized onto a sensor surface and the
interaction with the biomolecules near it cause a refractive index change. A large number of applications in life
sciences, including binding kinetics of receptor-biomolecule pairs and virus-protein interactions, are using
evanescent wave-based biosensors for their studies. This article describes the technology behind their sensing
techniques, and a range of applications where they are used.
I. Introduction
The first biosensor is considered the enzyme electrode transducer developed by Updike and Hicks [1].
Its working principle served as the base for the many other biosensors developed so far. Almost all of them
incorporate a sensitive biorecognition layer and a physicochemical transducer, which converts a biochemical
signal to an electronic or optical signal, as shown in Error! Reference source not found.. The recent
developments in nanotechnology have improved the quality of biorecognition elements used in biosensors,
which are typically synthesized in a laboratory. Nowadays the most popular biosensor is the one detecting the
glucose concentration in blood, due to the wide spread of diabetes in developed countries [2]. The glucose
monitoring technology has been improving for almost thirty years now, and as result people today can monitor
their diabetes with small, fast, cheap and easy to use glucose biosensors [3].
Many other biosensing devices have been developed so far, using metal oxide semiconductor
technology (CMOS), which are used in biomedical applications such as pregnancy, bacterial infection,
cholesterol and troponin T quick tests [4].
The detection using the traditional methods, like PCR and ELISA, are still popular today because they
are very selective and reliable, but gradually nowadays they are becoming too slow. Optical biosensor
technology promises equally reliable results but in much shorter time, and their potential market is very
encouraging. However, their cost and complexity is a drawback and much work needs to be done in order for
them to become a real alternative. Biosensors need to show that they are capable of reaching at least the same
detection levels as traditional techniques,
Fig. 1 Biorecognition and transduction layer elements in a biosensor design (Chambers et al., 2008). Reprinted
from “Biosensor Recognition Elements” by J. P. Chambers, B. P. Arulanandam, L. L. Matta, A. Weis and J. J.
Valdes, 2008, Current Issues in Molecular Biology, 10, p. 1. Copyright 2008 by Horizon Scientific Press.
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but with a lower cost [5, 6]. Improving metrics such as sensitivity, cost, and ease of use of a biosensor
can have a big impact on their commercial success [7]. Electrochemical techniques generally classified
according to the observed parameter: current (amperometric), potential (potentiometric) or impedance
(impedimetric) offer lower cost but these techniques present more limited selectivity and sensitivity than their
optical counterparts [8].
Detecting the biological analytes directly through their physical properties (such as mass, size or
electrical impedance) presents many difficulties, therefore scientists have been using some sort of “label”
(mainly fluorescent or magnetic substances) which attach to the molecules, viruses or cells being studied. The
label indirectly indicates the presence of the analyte to which it has been attached by identifying its color or
detecting the photons generated at a particular wavelength [9, 10]. However, although the use of labels gives a
very good sensitivity, their usage causes many other side effects. In general, this treatment results in the death of
the specimen, which prevents the ability to study a single population repeatedly over a long time. Also, the use
of labels requires special labs and large quantities of reagents and equipments that must be properly disposed.
The loss of color of the fluorescent chemical compound over time due to exposure to light reduces the ability of
this technique to supply measurements in high quantity. In case when nanoparticles are used as labels, their use
requires a high degree of development to assure that the label does not block the attached molecule or modify its
shape or structure [7]. The hydrophobic nature of fluorescent compounds used in labeling makes them have a
tendency to form clusters in the solution, creating background binding which is a significant problem leading to
errors in detection [11]. The interaction strength between the target molecule and receptor is indicated by the
intensity of the fluorescence. The signal generated by the fluorescent substance and the fact that the number of
fluorophores on each molecule cannot be precisely controlled, makes it difficult to make a quantitative analysis
[12]. Due to these disadvantages, there has been a drive to develop methods that allow direct detection of
biological analytes without labels, which would reduce cost and complexity while providing more quantitative
information.
By detecting analytes in their natural form, label-free detection removes the experimental uncertainty
induced by the effect of the label and in general it measures the refractive index change (RI) induced by
molecular interactions. The RI change is related to the sample concentration, while the detection signal usually
depends on the total number of analytes in the volume. As a result, the detection signal does not scale down with
the sample volume. This characteristic makes label-free detection advantageous over label-based detection and
particularly attractive when ultra small (femtoliter to nanoliter) detection volume is involved [12].
One way of label-free sensing is by using optical techniques, where in general an optical waveguide confines an
electromagnetic wave in such a way that it can interact with a test sample. The electromagnetic wave may be a
traveling or a standing wave, depending on the sensor configuration, but in both cases the structure must be
designed so that the extending wave from the waveguide surface can penetrate into the test sample. This
extending wave has an exponential decay in its intensity and is called the evanescent field. Back in 1970s,
evanescent waves were used to study ultra-thin metal films and coatings [11]. The evanescent field extends only
∼100–150 nm into the test sample for the typical wavelength range for optical biosensors (600–900 nm),
therefore it can make a good discrimination between the analyte attached to the receptor near the surface and the
unbound material suspended in the solution. One key to high sensitivity sensor design is to match the regions of
greatest biochemical binding to those with the highest evanescent field intensity [7].
In evanescent field based detection the biomolecular interaction affects the guiding properties of the
waveguide due to the change in refractive index. The change in refractive index can then be evaluated by the
optical properties of the waveguide such as intensity, phase, polarization, etc, which can then be correlated with
the concentration of the analyte, resulting in a quantitative value of the interaction [13]. Biosensors based on
evanescent field detection have shown to be very good candidates for point of care devices due to their extreme
sensitivity for label-free and real-time sensing. Their detection limit is close to 10-7
-10-8
in bulk refractive index.
Other evanescent field biosensors are those using Surface Plasmon Resonance (SPR), which is based on the
variation of the reflectivity on a metallic layer in close contact with a dielectric media. Their sensitivity goes to
10-5
– 10-7
RIU in bulk and 1-5 pg/mm2
in surface, but one drawback of SPR sensors is that they have a
relatively large size making their integration in Lab-on-Chip (LOC) platforms difficult. Today, the few
commercialized IO biosensors present on the market are expensive and not truly portable. Many progresses have
been done in this direction due to advances in silicon technology but there are still limitations in the integration
of all the components into one single system [14].
The main advantage of evanescent based mechanism is that it is not necessary to separate in advance
the nonspecific components because any change in the bulk solution will hardly affect the sensor response.
Therefore, the evanescent field mechanism is very useful for label-free detection of analytes or biochemical
reactions in complex real samples. The major contributing factor to the sensitivity of a system is the strength of
light-matter interaction. For a sensing system the smallest amount of analyte that produces a measurable output
signal is defined as the detection limit (DL) for that system. It can be specified in two main ways: a) according
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to the changes in the bulk refractive index of the solution above the sensor surface (expressed as refractive index
units (RIU)); b) according to the surface sensitivity, related to the accumulation of mass on the sensor surface,
normally expressed as surface mass density (pg/mm2
). The best resolutions for bulk refractive index changes are
within the range of 10-7
to 10-8
RIU, which depending on the analyte and transducer mechanism means that
concentrations down to ng/ml or pg/ml can be determined [13].
Fig. 2 Schematic working principle of a planar waveguide interferometer. The binding of analyte to the
receptors causes a refractive index change near the surface, n. This change induces a phase shift, , of the
signal in the measuring channel relative to the reference one, which is measured based on their interference.
On the other hand waveguide interferometers lack some specific features and have some drawbacks
compared to the other sensors. One of them is that only relative parameter values (related to a reference) can be
gained from a waveguide interferometer. Additionally, they are highly sensitive for wavelength instabilities.
Consequently, temperature stabilized light sources need to be applied in order to avoid wrong interpretation of
the measurement. Furthermore, in order to suppress the non-negligible effects of mechanical vibrations and
temperature changes, the sensor unit has to be stabilized and properly isolated from the environment. The future
challenge is to design waveguide interferometer sensor systems, which are capable of detecting and
investigating bio-chemical reactions with improved sensitivity and detection limit, without the aforementioned
disadvantages, and suitable for point-of-care applications.
II. Theory of planar optical waveguide interferometers
2.1 Principles of optical interferometry
The interference phenomenon first studied by Isaac Newton, who observed the interference fringes in
the form of concentric rings formed from a light source after passing a plano-convex lens, could not be
explained by simply regarding light as rays that propagate along straight lines. English physicist Thomas Young
explained Newton's rings as an interference phenomenon, which is a characteristic of waves. His double-slit
experiment in 1804 [15], was an undeniable fact and very important in accepting the wave theory of light at that
time. Based on this phenomenon four basic interferometers were developed which find usage in biosensing.
Michelson, Fabry-Perot, Mach-Zehnder, and Young interferometer [16]. These devices use optical
interferometry for measuring small changes that occur in an optical beam along its path of propagation.
Michelson interferometer finds a lot of use in infrared spectrometry for spectral identification of a compound
structure [17]. It divides a beam of light into two different paths and then recombines them after introducing a
difference in the two paths. As the difference in path length changes, the interference creates variations in output
intensity. The intensity variations can be measured with a detector as a function of the path difference. The
Fabry-Perot interferometer known also as the etalon is widely used in telecommunication, lasers and
spectroscopy to control and measure the wavelength of light [18]. It uses a resonant cavity formed by placing
two mirrors facing each other and provides very long path lengths as light bounces back and forth in the mirrors
thousands of times. Long optical path designs allow very sensitive measurements of the absorption and
refractive properties of a compound. Nevertheless, these configurations have found limited application in
sensors due to the fact that they need prior reference measurements to be taken with an empty cavity and the
moving mirrors introduce some additional complexity [19].
A practical sensor would have no moving parts, making it simple to implement, and would be able to
make real-time monitoring. These features are offered from Mach-Zehnder and Young interferometers which
have a wider use in biochemical measurements.
2.2. Young and Mach-Zehnder interferometer
In Young interferometer (YI) [20] and Mach-Zehnder interferometer (MZI) [21] the polarized input
beam splits and propagates in different arms. In the sensor arm the beam interacts with the sample of interest,
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while on the other, called the reference arm, the beam may be insulated from the environment or interacts with a
reference sample. When a change happens in the sample it shifts the phase of the beam in the sensor arm
compared to the one in the reference arm. In MZI the beams are recombined again in the same channel towards
the photodetector, while in YI the output beams propagate in free space until they overlap and form an
interference pattern on a CCD camera, as shown in figure 3.
Fig 3. Typical (a) Mach-Zehnder Interferometer (MZI) and (b) Young Interferometer (YI) configurations.
Reprinted from “Integrated planar optical waveguide interferometer biosensors: A comparative review” by P.
Kozma, F. Kehl, E. Förster, C. Stamm, F.F. Bier, 2014, Biosensors and Bioelectronics, 58, p. 291. Copyright
2014 by Elsevier B.V.
In MZI the measured intensity, I, is a periodic function of the phase shift difference, , between the beams.
I=I1+I2+2 𝐼1 𝐼2cos(∆) (2.1)
The phase shift difference between the two beams traveling in two different paths, L1 and L2, can be calculated
as [22]:
∆ = 𝑘0 𝑛 𝑟 𝑑𝑟 − 𝑛 𝑟 𝑑𝑟
𝐿2𝐿1
(2.2)
where k0 = 2/0 and 0 are the wavenumber and the wavelength in free space, while n(r) is the refractive index
of the medium at point r.
In YI the optical path length of output beams varies in the y axis, therefore the intensity of the resulting
interference pattern can be calculated as [23]:
I(y) =(y)I1+I2+2 𝐼1 𝐼2cos( 𝑦 + ∆) (2.3)
where =l/kd is the spatial period of the fringes, k=k0n=2/ is the wavenumber of the medium, d the spacing
between the channels, while l is the distance between output plane and the detector. The coefficient(y)
represents the diffraction on a single slit of width b, which modulates the intensities of the interference fringes.
The difference between these two approaches lies in the fact that in MZI the intensity is related to the phase
difference of the two beams, while in YI the position of the interference fringes is proportional to the phase
difference of the beams.
A well known integrated MZI structure used in opto-chemical sensing which offers very high
sensitivity is described in [24], while an ultrasensitive application of an integrated optical Young interferometer
used for the real-time direct detection of viruses is reported in [25]. The sensitivity of this sensor is high enough
to detect the presence of a single virus particle and represents a device of unprecedented sensitivity with a wide
range of applications. Recently, a multichannel interferometer design based on MMI couplers is under
development, which has a working principle similar to integrated optical Young interferometer, but offers a
smaller footprint and more measuring channels [26].
2.3. Wave propagation in planar optical waveguides
The phenomenon of total internal reflection used today for guiding the light in a waveguide was first
demonstrated by Daniel Colladon with his „light fountain” experiment in 1841 and then by John Tyndall in 1854
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[27, 28], where light remained confined to a falling stream of water. This phenomenon was later used in many
applications, such as in telecommunication and sensor devices for the confinement and guidance of
electromagnetic waves with high efficiency. The telecommunication industry developed novel methods to
couple and transfer light in optical waveguides for high speed communication, while the semiconductor industry
developed technologies for the fabrication of complex integrated optical (IO) systems [29]. A simple waveguide
consists of three layers: a) a cover (C), b) a film (F) and c) a substrate (S), with refractive indices nC, nF, and nS,
respectively. In order for the light to be guided, the total internal reflection condition must be met, as shown in
Error! Reference source not found.. The refractive index of the film must be higher than that of the cover
and substrate (nC < nF >nS), and the angle of propagation relative to the interface normal must be larger than the
critical angle, C, at the two boundaries. Based on Snell‟s law the critical angle is measured as C =
arcsin(nS,C/nF) [30].
Fig 4. Light propagation in a planar optical waveguide. Light can be coupled and guided in a waveguide if nC <
nF > nS and if the angle of light propagation relative to the interface normal is larger than the critical angle C.
In order for a wave to be guided in a waveguide it must fulfill the so-called self-consistency (also
known as transverse resonance) condition, whereby as the wave reflects from the boundaries it must reproduce
itself by constructive interference. In short, this means that the phase shift between the reflected waves from the
two boundaries must be equal, or different by an integer multiple of 2. Fields that satisfy this condition are
called the modes or the eigenfunctions of the waveguide. They maintain the same transverse distribution and
polarization at all locations along the waveguide axis [31].
Fig. 5 Field distribution of different modes in a dielectric planar waveguide. Adapted from Fundamentals of
Photonics (p. 304), by B.E.A. Saleh and M.C. Teich, 2007, New Jersey: John Wiley & Sons. Copyright 2007 by
John Wiley & Sons, Inc.
Let‟s take in consideration a coordinate system where the modes propagate in the z axis, while the x
and y axis are perpendicular and parallel to the planar waveguide interfaces, respectively, as shown in Error!
Reference source not found.. The plane wave solutions of Maxwell equations for this waveguide show
that only transverse electric (TE) or transverse magnetic (TM) modes can be excited. The boundary conditions
of wave propagation in planar waveguides [30], imply that the wavevector of original, refracted and reflected
waves must lie in a plane, and also the tangential component of the wavevector across an interface should be
continuous. The effective refractive index N, (nC <N < nF), for planar waveguides is defined as 𝑁 = 𝑘 𝑡 𝑘 ,
where 𝑘𝑡 = is the tangential component of the wavevector 𝑘, or the propagation constant [32].
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Fig 6. Visualization of a) TE mode and b) TM mode. In planar optical waveguides either the total electric or the
total magnetic field can oscillate in the plane of the interfaces.
In case of TE polarization there is no electric field in the direction of beam propagation. In this case the
boundary conditions are:
TE: Ex = 0, Ez = 0, Hy = 0, ky = 0 thus Ey, Hz ,
𝜕𝐸 𝑦
𝜕𝑥
are continuous. (2.1a)
In case of TM polarization there is no magnetic field in the direction of beam propagation. In this case the
boundary conditions are:
TM: Ey = 0, Hx = 0, Hz = 0, ky = 0 thus Ez, Hy,
𝜕𝐻 𝑦
𝜕𝑥
are continuous. (2.4b)
The minimum thickness of the waveguide film for which at least one mode can be guided is known as the “cut
off” thickness of the waveguide, [33]. For TE and TM polarization the “cut-off” thickness is calculated as [34]:
𝑑 𝐹 𝑚
𝜌
=
1
2
𝑛 𝐹
2
− 𝑛 𝑆
2 −1/2
× 𝑚 + 𝜋−1
𝑎𝑟𝑐𝑡𝑎𝑛
𝑛 𝐹
𝑛 𝐶
2𝜌 𝑛 𝑆
2
− 𝑛 𝐶
2
𝑛 𝐹
2
− 𝑛 𝑆
2
1 2
(2.5)
where =0 for TE modes and =1 for TM modes. In the field of biosensing, it is of general interest to build
waveguides with high optical sensitivity constants. This waveguides usually have a very thin film with high
refractive index. It is shown that a waveguide with a very small “cut-off” thickness can be achieved if the
difference between the refractive indices of the film and the substrate is approximately nF – nS 0.3 [34].
The total electromagnetic field propagating inside a waveguide can be given as a linear combination of an
upward E+
(x,z,t), and downward E-
(x,z,t), propagating wave, as shown in Error! Reference source not
found. [32]. In case of a TE field we can write:
E (x,z,t) = E+
(x,z,t)+ E-
(x,z,t) = 𝐸0
+
𝑒 𝑖𝑘 𝑥 𝑥−𝑥0 +𝜑+
+ 𝐸0
−
𝑒−𝑖𝑘 𝑥 𝑥−𝑥0 +𝜑−
𝑒 𝑖𝑁𝑘0 𝑧−𝑖𝜔𝑡 (2.6)
where E0 is the amplitude, kx the wavenumber component in the x direction, while 𝜑+
and 𝜑−
are the initial
phase of the upward and downward propagating waves, respectively. We could write the same for a transverse
magnetic (TM) field by substituting E with H.
Outside the waveguide film the amplitude of the propagating wave attenuates exponentially with the distance
from the interface, forming the evanescent wave. Its penetration depth in the cover medium is the distance at
which the field decays by a factor of 1/e and can be calculated by [32]:
𝜹 𝒆 =
2𝜋 𝑁2 − 𝑛 𝐶
2 (2.7)
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Fig. 7 Visualizaton of mode formation in a planar optical waveguide. The total electromagnetic field inside the
waveguide film is composed by the superposition of an upwards E+
(x, z, t) and a downward E-
(x, z, t)
propagating wave. Adapted from “Integrated planar optical waveguide interferometer biosensors: A
comparative review” by P. Kozma, F. Kehl, E. Förster, C. Stamm, F.F. Bier, 2014, Biosensors and
Bioelectronics, 58, p. 293. Copyright 2014 by Elsevier B.V.
We can calculate the Fresnel reflection coefficients, rS and rC, for the substrate and cover, as follows [35]:
𝑟𝑠 =
𝐸0
+
𝐸0
− = 𝑟𝑠 𝑒 𝑖𝜑 𝑠 (2.8a)
𝑟𝑐 =
𝐸0
−
𝑒−𝑖𝑘 𝑥 𝑑 𝐹
𝐸𝑒 𝑖𝑘 𝑥 𝑑 𝐹
= 𝑟𝑠 𝑒 𝑖𝜑 𝑐 (2.8b)
where s and c, are the phase shifts due to reflection from the substrate and cover, respectively. These phase
shifts are different for TE and TM modes therefore they propagate under different conditions. Inserting Eq.
(2.8a) into Eq. (2.8b), the mode equation becomes:
𝑟𝑠 𝑟𝑐 𝑒2𝑖𝑘 𝑥 𝑑 𝐹 = 𝑟𝑠 𝑟𝑐 𝑒 𝑖(𝜑 𝑠+𝜑 𝑐+2𝑘 𝑥 𝑑 𝐹)
= 1 (2.9)
The solution of Eq. 2.9 defines the transverse resonance condition of the guided modes:
2𝑘 𝑥 𝑑 𝐹 − 𝜑𝑠 − 𝜑𝑐 = 2𝜋𝑚 (2.10)
where m is the mode order.
Although the critical angle, θC, does not depend on the polarization of the wave, the phase shifts, S and C,
caused by the internal reflection at a given angle depend on the polarization. Therefore, TE and TM waves have
different solutions for the transverse resonance condition. For a given polarization, the solution of the transverse
resonance condition yields a smaller value of θ and correspondingly a smaller value of β for a larger value of m.
Therefore, higher order modes travel with a smaller propagation constant than lower order modes, β0 > β1 > β2 >
…. Only discrete values of θ = θm can satisfy the resonance condition, because m can assume only integer
values. This results in discrete values of the propagation constant, βm, for the guided modes. The guided mode
with m = 0 is called the fundamental mode and those with m = 1, 2, … are higher-order modes. Because we are
considering an asymmetric waveguide where nC< nF >nS, the TE and TM fields have unequal amplitudes and
decay at different rates at the two boundaries [36]. If the thickness of the waveguide and refractive index
contrast between the film and the surroundings is increased, the number of guided modes is also increased; on
the other hand the increase of the wavelength decreases the number of guided modes [31].
Error! Reference source not found. depicts the field-distribution profiles of the first four modes, i.e.
TE0, TM0, TE1 and TM1 in planar optical waveguides. When only the fundamental modes are supported, the
waveguide is called single-mode [31]. A typical dielectric single-mode waveguide thickness is about 100-200
nm.
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Fig. 8 Schematic visualization of the waveguide modes in a planar optical waveguide. The field-distribution
profile of the modes for TE and TM polarization are presented. As it is depicted, TM modes penetrate deeper
into the surrounding media than TE modes.
2.4. Sensing with the evanescent field
The main problem of the sensors today is the low interaction between the evanescent field and the
measurand. This interaction is proportional to the evanescent field penetration depth in the cladding, which has
an upper limit of 100–150 nm. For this reason, the monitoring of biomolecuar binding events has been focused
near the sensor surface not exceeding this distance. To overcome this limit, the reverse symmetry configuration
was recently proposed [37]. The reverse configuration offers deeper penetration of the evanescent
electromagnetic field into the cover medium, theoretically permitting higher sensitivity to analytes compared to
traditional waveguide designs. By introducing a low-refractive-index layer between the substrate and the film
the probing distance of the evanescent field can be increased to about 1 m. This increases the effective area of
detection and can detect refractive index changes deep inside the cells and far from the surface. This directly
contributes to the increase of sensitivity but is a drawback to specificity because it detects other particles present
in the analyte [38]. A large penetration depth can also be obtained for small substrate refractive indices and thin
films with high refractive indices [39]. Large film thicknesses lead to a small penetration depth. In this case the
effective refractive index, N, will approximately reach the value of the film refractive index, N ≈ nF. In case of
SPR sensors there is a limited possibility in varying the penetration depth because it is limited to a range of
about 180 – 230 nm. Due to the limited penetration depth the disturbing effect of unwanted variations of the
bulk refractive index is 2 – 3 times higher compared to IO sensors [39]
In waveguide based sensors the evanescent field is used for sensing binding events in an analyte in
close proximity to the surface. When a binding event happens, it changes the refractive index in the near-
interface region, which in turn changes the effective refractive index, N. This has an effect on the wavelength of
the guided light causing a phase shift relative to a reference beam. For an interaction length, L, the phase shift
difference induced in the guided mode due to any refractive index change in the sensing region can be measured
as:
∆ =
𝜕
𝜕𝑁
𝜕𝑁
𝜕𝑛 𝑐
∆𝑛 𝑐 +
𝜕
𝜕𝑁
𝜕𝑁
𝜕𝑑 𝐴
∆𝑑 𝐴 = 𝑘0 𝐿𝑆𝑐∆𝑛 𝑐 + 𝑘0 𝐿𝑆𝐴∆𝑑 𝐴 (2.11)
where SC = 𝜕𝑁/ 𝜕𝑛c is the sensitivity to cover refractive index changes and SA = 𝜕𝑁/ 𝜕𝑑A is the sensitivity to
adlayer thickness change [40]. By fine tuning the opto-geometrical parameters of the waveguide configuration
the values of SC and SA can be maximized. The use of integrated optical waveguides in biosensing brings a great
advantage due to the flexibility that they offer in choosing different materials and designing structures [41].
An important parameter used in biosensor applications is the adsorption of molecules on the sensor surface. It is
very useful to quantify an experiment and is usually measured in mass per unit area. It is called surface mass
density, Γ, of a protein adlayer and can be calculated using De Feijter‟s formula:
𝛤 = 𝑑 𝐴
𝑛 𝐴 − 𝑛 𝑐
𝜕𝑛/𝜕𝑐
(2.12)
where nA is the adlayer refractive index and 𝜕𝑛/𝜕𝑐 is the derivative of solution refractive index with respect to
protein concentration [42].
Another important parameter in biosensing which creates the possibility to simply and objectively compare the
different existing biosensor configurations is the Detection Limit (DL). It is defined as the smallest parameter
change that can be detected with reasonable certainty in a configuration. In accordance with the confidence level
needed, a confidence factor k is defined. A general formula to calculate the DL is [43]:
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𝐷𝐿 = 𝑘
𝜍
𝑆
(2.13)
where is the standard deviation of the blank signal and S the sensitivity. In biosensorics, k is generally chosen
3, because it gives a 0.13% chance that a signal measured at the limit of detection would be the result of random
fluctuation of the signal, and not a meaningful change. In optical label-free sensors there are typically three
ways to specify the DL. The first is to specify it in refractive index units (RIU) since these sensors are sensitive
to the RI change in bulk solution. This gives the possibility to make a rough comparison of the sensing
capability among different optical technologies and structures. The second way is to use surface mass density
(or total mass) in units of pgmm−2
. It reflects the intrinsic detection capability of a sensor and can be used to
evaluate or compare the sensor performance. The drawback is that experimentally it is difficult to determine
surface mass density accurately. The third way is to use sample concentration (in units of ngml−1
or molarity). It
is easy to determine from an experiment as no detailed information regarding the mass density on the surface is
needed. These three DLs are correlated and the relationship between them needs to be studied for each
individual optical biosensor [12].
2.5 Waveguide types
Today, there are various configurations in material and geometry of planar optical waveguides.
Depending on their geometrical design they can be classified in two main types: 1) slab waveguides and 2)
channel waveguides [44]. Slab waveguides have a planar geometry and guide light only in the transverse
direction. [45]. They are easy to fabricate and there is no scattering between the transverse and lateral modes.
Channel waveguides offer two dimensional optical confinement and act as a pipe for guiding the light. They
exist in different configurations as shown in Error! Reference source not found.; buried, diffused, ridge, rib,
strip-loaded, and ARROW waveguides [29]. A buried waveguide is imprinted in the substrate and completely
surrounded by the cladding material. Therefore, it is suitable for guiding the light but not a convenient
configuration for the sensitive area of a biosensor.
Fig 9. Schematic 3-dimensional representation of different waveguide types. The same functional layers are
marked with the same colours.
In case of the diffused waveguide the high-index region in the substrate is formed through diffusion of
dopants, such as Ti, or by ion exchange. Due to the diffusion process, the film boundaries in the substrate are
not sharply defined [46]. A strip-loaded waveguide is formed by loading a planar waveguide, which already
provides optical confinement in the transverse direction, with a dielectric or a metal strip to facilitate optical
confinement in the lateral direction. The waveguiding film of this waveguide is the region under the loaded
strip, with its width determined by the width of the loaded strip. Again this configuration is not suitable for
biosensing due to the shielding of the film [36].
A ridge waveguide has a structure similar to the strip waveguide, but the ridge in this case is actually
the waveguiding film. A ridge waveguide has a strong optical confinement because it is surrounded on the three
sides by low-index material (air, substrate or cladding).
In case of the rib waveguide, the strip or the ridge has the same refractive index as the high index planar layer
beneath it and is part of the waveguiding film. The ridge and rib waveguide are very common in the field of
optical planar waveguide biosensors [47]. The Anti-Resonant Reflecting Optical Waveguide (ARROW) is an
alternative to the rib waveguide configuration. The light is guided in the waveguide rib due to the total internal
reflection at the air-film interface and the high anti-resonant reflection (>99.9%) from the interference cladding
10. Interferometric Evanescent Wave Biosensor Principles and Parameters
DOI: 10.9790/4861-07618496 www.iosrjournals.org 93 | Page
layers, which behave as Fabry-Perot resonators operating at their antiresonant wavelengths. They separate the
waveguide film from the substrate and have an effective single-mode behavior. They present low losses for the
fundamental mode and filter out higher order modes by loss discrimination. Compared to the total internal
reflection waveguides ARROW waveguides offer larger film thickness, greater parameter tolerance in
fabrication and lower losses [48, 49]. Both slab and channel waveguides can be divided in step-index, graded
index and photonic crystal waveguides, depending on their refractive index profile. When the refractive index
exhibits abrupt changes between the waveguide film and the cladding it is called a step-index waveguide, while
when the refractive index varies gradually and has a smooth transition to the cover or substrate, it is called a
graded-index waveguide. The most common materials used to form the thin layer of high refractive index in
step-index waveguides are Ta2O5, TiO2, Si3N4, A12O3 or SiON [50, 51]. Graded-index waveguides can be
fabricated by implementing both light and heavy ions, with the combination of other techniques as
photolithography, etching and ion exchange. Good quality graded-index waveguides can be fabricated in glass
by femtosecond laser pulses [52, 53]. The high contrast in refractive index that is achieved in step-index
waveguides ensures good guidance conditions and optimizes the evanescent field distribution in the film-cover
interface compared to graded-index waveguides, therefore they offer better sensitivity [54]. Error!
Reference source not found. shows refractive index variations in step-index and graded-index
waveguides.
Fig. 10. a) Step-index and b) graded-index waveguide. Step-index waveguides exhibit an abrupt refractive index
step at the substrate and cover transitions, while the refractive index profile of graded-index waveguides has a
smooth transition between them.
2.6 Light Coupling Techniques in Waveguides
In order for the light to be guided in a waveguide it first needs to be coupled in it from an external
source. The five main coupling techniques used with planar waveguides are: a) end-fire-, b) butt-end-, c) prism-,
d) grating and e) directional coupling, as depicted in Error! Reference source not found. [31, 55]. In end-
fire coupling the light is directly focused on a cleaved end face of the waveguide. This is the simplest way to
couple a free-space source into a waveguide, but on the other side it has some drawbacks as it needs a very
precise alignment of the incident light relative to the waveguide due to the small dimensions of the waveguide
slab. Focusing and alignment in this case are usually difficult and coupling efficiency is low especially in thin
single-mode waveguides. For efficient coupdsfling the transverse distribution and the polarization of the
incident light must match that of the desired mode and the numerical aperture of the focusing lens needs to be
fitted to the propagation constant of the mode excited in the waveguide.
11. Interferometric Evanescent Wave Biosensor Principles and Parameters
DOI: 10.9790/4861-07618496 www.iosrjournals.org 94 | Page
Fig. 11. Light coupling techniques for optical waveguides a) end-fire coupling, (b) butt-end coupling c) prism
coupling, d) grating coupling and (e) directional coupling
The butt-end coupling is a closely related concept to free space end-fire coupling. It couples the light
from a semiconductor source such as a light-emitting diode or a laser diode, or by bringing in contact an optical
fiber with the cleaved end face of a waveguide, leaving a small space between the two physical units for
maximum coupling. Similarly to end-fire coupling, the alignment is crucial as well as the mode matching
between them. It is generally easier than the alignment of a light cone as in the case of end-fire coupling
(especially for wavelengths beyond the visible spectrum), and can be done under a microscope [56]. When a
prism with a high refractive index is used to couple the light into the waveguide film, the method is called prism
coupling. The prism is either placed at a short distance from the waveguide or is brought in direct contact with it
by applying mechanical pressure or by the use of immersion oil. The incident wave is refracted into the prism
and undergoes total internal reflection at an angle P. The incident and reflected waves form a wave traveling in
the z direction with a propagation constant P = nP k0 cos , where nP is the refractive index of the prism. In the
space separating the prism and the slab waveguide extends the exponentially decaying evanescent wave of the
field traveling into the prism. If the distance between the prism and the waveguide is sufficiently small, the
wave is coupled into a mode of the slab waveguide with a matching propagation constant m ≈ P = nP kC cosP,
where kC is the wavenumber of the cover medium. This method offers high efficiency not only for coupling the
light into the waveguide but also for extracting it. Due to the mechanical pressure or immersion oil applied when
in direct contact with the waveguide, this method is not convenient for sensing applications because the applied
pressure can lead to slight waveguide deformations, whereas the immersion oil may contaminate the waveguide
surface [57].
Waveguide grating couplers have a periodic alternating effective refractive index, usually in the range
of the wavelength [58, 59]. The grating coupler consists of a periodically corrugated surface, realized by
embossing or photolithographic processes or an alternating modification of the waveguide refractive index. The
modification of the refractive index can be achieved by ion exchange or UV induced refractive index
modulation [60]. The phase-matching condition in grating couplers is achieved due to the phase modulation of
the incident wave from the periodic structure of the grating coupler. A grating with period Λ modulates the
incoming wave by a phase factor 2q/Λz, where q = ±1, ±2, . This is equivalent in changing the z component
of the wavevector by a factor 2q/Λ. The phase matching condition can now be written as m = nC kC cosi +
2q/Λ, where i is the incident angle, while nC and kC are the refractive index and wavenumber of the cover
medium, respectively [61]. This technique has various advantages compared to the other mentioned methods: a)
The fact that only the coupling angle on the incident beam needs to be adjusted in order to achieve the phase-
matching condition, makes this coupling technique rather easy to implement. b) Contrary to the prism coupler
light can be coupled via the substrate, besides via the cover. This eliminates the problem that exists in prism
coupling configuration, where light is obstructed from fluidic chamber placed on the cover of the waveguide.
Additionally, no immersion oil is needed in this configuration. The main drawbacks are that the production of
the waveguide gratings is technology-intensive, and they are very sensitive to mechanical vibrations, since the
coupling efficiency is very sensitive to the angel of incidence [62].
In directional coupling a mode is excited in a channel waveguide via the evanescent field of another
waveguide in close proximity with the first one [63]. In other words, one of the waveguides acts as the source
for the other, and the amount of optical power that can be transferred between them is related to some
geometrical parameters such as interaction length and their relative interdistance. In general, the length of the
waveguides in close proximity necessary to transfer the power completely for one waveguide to another is
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DOI: 10.9790/4861-07618496 www.iosrjournals.org 95 | Page
called coupling length, L0, or the transfer distance. At half of the distance, L0/2, half of the power is transferred
and the device is called a 3-dB coupler, i.e a 50/50 beam splitter. Directional coupling is mainly used in signal
multiplexing or for coupling light into ring resonators, where this mechanism is necessary. Similar to grating
coupling this method has the disadvantage that is technology-intensive, and analog to butt-end coupling the light
needs to be previously coupled into one of the waveguides.
III. Conclusions
After a short presentation of the theory behind the working principle of interferometer biosensors, were
presented some of the most important parameters to be taken in consideration. The combination of planar
waveguides with interferometry techniques to realize detection of analytes in a sample, led to the realization of
multiple configurations for the biosensors without labels, with very good characteristics and detection limits
compared to other sensing devices. As shown in this review, interferometric biosensor abilities have
dynamically improved during the last 20 years. Nowadays, it is possible with these devices to detect the
presence of even small molecules that are deposited or connected onto a sensing surface. As it is shown,
nowadays is achieved a detection limit of 0.1 pg/mm2
[64].
Nevertheless, from the technological point of view there are some problems to be solved in order for
these devices to be considered portable and usable maybe from the patient himself. The need for coherent
quality light sources, which are still big and require a lot of power, stabilized coupling of light, an efficient
cancellation of electrical and mechanical noises, and an efficient control of temperature in order to reduce
measurement noise, make this configurations difficult to be completely integrated into portable devices.
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