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Spaser Amplifier for Small Signal Detection for Raman Scattering Measurements of a Single Molecule of BSA
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Spaser Amplifier for Small Signal Detection for Raman Scattering Measurements of a Single Molecule of BSA

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Originally part of a presentation: …

Originally part of a presentation:
Detection of a single BSA molecule by amplifying its Raman signal.
Done with my friend: Pemba Lama
[I came up with the idea for amplifier (and detector scheme) so that is what I have posted]
For Course Project: Nano and Micro Photonics
Under Prof. Vinod Menon, Queens College and Graduate Center, CUNY


The project was devised so that students come up with original ideas, based on known physical principles, for the detection of a single molecule of BSA (a biological molecule). Unfortunately, this means we could not verify the validity of the work, and my work is no exception. It is my hope that I have not overlooked any relevant physical principles, and that this kind of amplifier is possible. If anyone finds my design promising then:
-I would certainly like to know the simulation and experimental results
-I would like credit in the resulting publication – Thanks.

The substrate work that I did prior to this (and the mis-conceived SPASER work that I previously came up with) is here:
http://www.slideshare.net/faissal.bd/spaser-amplifierforsmallsignaldetectionforramanscatteringmeasurementsofasinglemoleculeofbsa
The SPASER work there is fundamentally flawed, but perhaps the substrate work is not entirely useless.

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  • 1. SPASER Amplifier Design for Small Signal (Raman Scattering) Detection from a Single Molecule (of BSA) Faisal Halim The City College of New York, CUNY Thursday, 13 th May, 2010 Originally part of: Detection of a single BSA molecule by amplifying its raman signal. Done with my friend: Pemba Lama [I have removed Pemba’s slides from this presentation as I have not asked for his permission to post them] [I came up with the idea for amplifier (and detector scheme) so that is what I have posted] For Course Project: Nano and Micro Photonics Prof. Vinod Menon, Queens College and Graduate Center, CUNY
  • 2. Raman Setup Excitation Laser SERS Substrate Substrate Movable Relative to Excitation and Detector Heads BSA Molecule Raman Scattered Spectrum Raman Scattering Detector
  • 3. Raman Signal Detection Scheme Weak Raman (SERS) Signals Multi-Layered SPASER Amplifier System Excitation energy for pumping gain medium Each color represents SPASER elements that amplify a particular wavelength
    • Wavelengths to amplify, and number of wavelengths chosen, based on:
    • choice of excitation wavelength
    • choice of scattering peaks used to identify the target molecule
    Light Collection Optics, Two Dichroic Mirrors, Avalanche Creating Electronic Detectors
  • 4. Raman Signal Amplifier SPASER Metamaterial Crystal Side View Front View Metamaterial SPASER Emitter SPASER Emitters for a given Wavelength SPASER Elements are arranged to intercept and amplify any incoming photon at any Wavelength Fluorescent Dye Gain Medium
  • 5. Spaser Emitter: A Closer Look Supporting Evidence from Existing Literature Source: 12 June 2006 / Vol. 14, No. 12 / OPTICS EXPRESS 5669 Source: PHOTONIC FRONTIERS: Subwavelength optics come into focus http://www.optoiq.com/index/photonics-technologies-applications/lfw-display/lfw-article-display/236205/articles/laser-focus-world/volume-41/issue-9/features/photonic-frontiers-subwavelength-optics-come-into-focus.html
    • Our SPASER Rings are optimized to:
    • Capture only light that hits dead on
    • Couple energy to emitting nano particle (NP) at center, which is the gain medium, by surface plasmon interactions
    • Capture only a specific wavelength (a narrow band)
    • If NP is already pumped by the excitation providing light source and a Raman Scattered Photon arrives we have stimulated emission
  • 6. Signal Detection Schematics (Conceptual) Shorter Wavelength gets reflected PMT or APD PMT or APD PMT or APD PMT – Photomultiplier Tube APD – Avalanche Photo Diode Dichroic Mirror
  • 7. Limitations
    • Poor Spatial Resolution
    • No time resolved measurements possible: too much uncertainty in emission times of radiation amplifying units.
    • This study has not accounted for scattering of photons impinging on the nano ring photo-antenna arrays.
    • This study has not investigated if both photons emitted by emitting the Nano Particle emitter at the center of the ring structure of the SPASER will propagate in the same direction
    • Limited Utility: Certainty of BSA identification predicated on number of types of photo enhancing NPs used (each type amplifying a different wavelength)
      • Possible Solution: Design a substrate that selectively outcouples Raman signal and emits it.
        • Problem with that: Method is lossy
      • Detection of any other molecule will require
        • Design and fabrication of new SPASER system.
  • 8. Another Proposal (presented in class, but put in here later): A Wavelength-Independent SPASER Amplifier System
      • Excite the target molecule on a broadband absorbing SERS substrate
      • Choose excitation wavelength from a supercontinuum source so that the Raman scattered peaks can be moved at will.
      • If possible, design a surface that sits close enough to the test molecule to evanescent mode outcouple Raman scattered signal from the target molecule and either couple it to a SINGLE Wavelength SPASER amplifier or emit it for detection by such an amplifier.
      • Move the wavelength exciting the molecule being tested so that one peak of its scattered signal is in resonance with the SPASER response and measure amplified signal intensity.
      • Move the excitation wavelength and measure the amplified intensity.
      • Measure amplified intensity for a range of excitation wavelengths.
      • Deconvolve SERS substrate surface plasmon coupling efficiency, the optical detector system’s signal strength vs. response characteristics and SPASER amplification factor from signal measured by the detector system.
      • Compare resulting graph of Raman Shift vs. Intensity with known Raman scattering data to identify the fingerprint of the signal from the test molecule.
      • SPASER amplification of Raman scattering is a new field ( DOI: 10.1021/nl903409x | Nano Lett. 2010, 10, 243-249 ), and further advances could enable the detection of Raman Scattering even when the excitation is not optimal due to mismatch of excitation wavelength and SERS substrate resonance wavelength. So, such a system could be possible.
  • 9. Conclusion
    • We have devised a SPASER with highly directional emissions (novel idea)
    • Raman Scatter Photons will trigger an increase in the signal strength (i.e. output power) of our SPASER (what we expect from our idea)
      • Note: Any spontaneous emission from the fluorophores in the SPASER will trigger SPASING, so the Raman signal will only modulate the SPASER output intensity.
    • Our highly directional SPASER will reduce the detection limit as it stands in a random SPASER paper: DOI: 10.1021/nl903409x | Nano Lett. 2010, 10 , 243-249
      • Metal Nanoparticles with Gain toward Single-Molecule Detection by Surface-Enhanced Raman Scattering
        • Authors: Zhi-Yuan Li,Younan Xia
  • 10. Personal Note:
    • The course project was devised so that students come up with original ideas, based on known physical principles, for the detection of a single molecule of BSA (a biological molecule). Unfortunately, this means we could not verify the validity of the work, and my work is no exception. It is my hope that I have not overlooked any relevant physical principles, and that this kind of amplifier is possible. If anyone finds my design promising then:
    • I would certainly like to know the simulation and experimental results
    • I would like credit in the resulting publication – Thanks.
    • Pardon my disclosure in using a non-peer reviewed outlet, but I do not know a group with the spare time to evaluate this idea, so I could not get to the (latter) stage of sending a properly evaluated idea to a peer reviewed journal. I hope you will understand.