1. Development of an Electrical Paper
sensor for the detection of a chemical
Dipak Gangapatnam - 13042016 Supervisor : Dr. Ashok Kumar Verma
Department Of Chemical Engineering and Technology
IIT(BHU) Varanasi
Oral examination M tech final year
2. Paper sensors :
Paper sensors have been constantly showing a great potential for realizing in
situ, simple and miniaturized in various areas including Basic scientific
advancement, clinical diagnostics, therapeutics and so forth.
The reason behind this being: 1) Simple instrumentation
2) Ease of operation
3) High sensitivity
4) low cost
5) Portability
6) Disposability
Introduction
3. By patterning paper with hydrophobic and hydrophilic barriers we can control the
flow of the sample.
Devices in some cases are built up in several layers to enable both sensing and
reporting capabilities.
Advantages : 1) The inherent capillary force between the channels within the
paper provides for the natural flow of the liquid.
2) No power sources required.
3) Low consumption of reagent and sample holds a lot of potential
for point of care and on site diagnostics.
How are they made..??
6. It is a device that can integrate miniaturized laboratory functions such as separation
and analysis of a mixture on a small microprocessor chip using extremely small fluid
volumes of the order of Nano liters and Pico liters.
Simply put it’s a very small scale laboratory where the real scale laboratory functions
take place.
Why use it….?
Low fluid volume consumption – less sample costs and volume.
Fast analysis and response times due to short diffusion distances.
Compactness of the system.
Lab on a chip
8. Develop an electrical paper sensor that is economical, compact and easy to use for
the detection of a chemical.
Literature review on sensors to obtain a clear picture to design and use a sensor.
Design a setup for experimentation
Prepare a lab on a chip for micro analysis
Measure the resistance of the solution with the help of the sensor and predict the
availability of sulphate ions .
Measure the resistance of a mixed solution i.e a precipitation reaction , with the
help of the sensor and predict the sulphate ion availability in the solution for
different concentrations.
Plot the values and find out the reason for their behavior.
Future suggestions to make the sensor better.
Objectives
10. A sensor is a device that detects events or changes in quantities and
provides a corresponding output.
The output is usually an electrical or an optical signal.
Examples:
A mercury thermometer converts the measured temperature Into
expansion and contraction of a liquid which can be visualized on the
calibrated glass tube.
A thermocouple converts temperature to an output voltage.
What is a sensor….?
11. Type of sensor Uses
Pressure sensor Gas turbines, power generation, elevator
switches etc.
Navigation and anti collision sensors Robots , fork lifters in malls, automobiles
Etc.
Leakage detection sensors Sewerage tunnel leakage detection,
Detection in industries
Humidity sensors Relative humidity
Gas sensors Various gases such as ozone , carbon di oxide
, methane etc.
Flow sensors Mass flow rate
Chemical sensors Ethanol detection ,DNA detection , hydrogen
sulfide , hydrocarbon/water vapor , chemical
oxygen demand etc.
12. Should be sensitive to measured property only.
Insensitive to any other property likely to be encountered in its
application.
The aforementioned “other property” shouldn’t influence the
measured property.
Minimal sensor deviations.
Attributes of a good sensor
13. Applications
• Electrochemical sensors are available for, e.g., SO2 , H2S, NO2 , COCl2 , CO
And O2(many gases).
• Biosensors and detectors for pesticides.
• Because of the low power requirements , small size and weightlessness :
• The electrochemical sensor is ideally suited for use in combination monitors,
that is, those that are able to monitor two or more substances at once.
• Papers sensors have been used for detection of heavy metal ions such as
Hg2+,Cd2+,Pb2+,Ag2+ and other toxic agents and carcinogenic pollutants.
These have also been used for temperature sensing and detection of acids ,
bacteria and various gases.
14. “Types ”
Physical sensors
A physical sensor is a device
that provides information
about a physical property of
the system.
Ex : pressure sensors,
temperature sensors etc.
Chemical sensors
A chemical sensor is a device
that transforms chemical
information, ranging from the
concentration of a specific
sample component to total
composition analysis, into an
analytically useful signal.
Ex: COD , methane , ions etc.
15. Classification of chemical sensors
Optical sensors
Electrochemical sensors
Electrical sensors
Mass sensitive sensors
Magnetic sensors
Thermometric sensors
Others – radiation detecting sensors
16. Components :
Receptor
The receptor is in contact with the
anlyte (i.e. the sample) and its prime
duty to provide high selectivity
towards the desired analyte in the
presence of other chemical species .
It also transforms the analyte
concentration into a chemical or
physical output signal with a defined
sensitivity .
[4]
17. Components :
Transducer
The transducer is another crucial
component of the sensor.
The transducer converts the signal
generated by the receptor to a
readable value .
[5]
18. Electrochemical sensors
• Sensors which transform the effect of the electrochemical interaction analyte
– electrode into a useful signal are known as electrochemical sensors.
• Such effects may be simulated electrically or may result in a spontaneous
interaction at the zero current condition.
• Types
1. Voltametric – Current is measured in the DC or AC.
2. Potentiometric - Potential is measured (reference electrode and working
electrode).
3. CHEMFET – Chemically Sensitized Field Effect Transistor.
4. Potentiometric Solid Electrolyte Gas Sensors – These are different from
potentiometric sensors because these work in high temperature solid
electrolytes and are usually applied for gas sensing measurements.
19. These sensors employ the combined characteristics
of the electrochemical sensors and paper sensors.
We measure an electrical quantity such as current,
resistance, voltage etc. This is the quality taken from
the electrochemical sensor.
And from the paper sensors it brings in several
advantages such a low sample volume, low cost,
ease of operation etc.
Electrical paper sensor
23. Geometric details of the sensor
Geometric detail Measurement
Length of the sensor 0.05 m
Breadth of the sensor 0.015 m
Thickness of the plastic sheet 0.002033 m
Thickness of the tissue paper 0.0001375 m
Thickness of the drawing sheet 0.0011 m
Diameter of the wire 0.0051 m
Thickness of the entire sensor 0.01 m
Area of the sensor 0.00075 m2
36. The first and the fore most result
observed is that the paper sensor
not only gives us the resistance
but also shows us the change in
colour when the solution is added
to it.
48. At low concentrations, the resistance decreases with increasing the
concentration upto 0.4N CuSo4 solution.
Thereafter the resistance increased slightly.
At high concentrations the variation is not much. The variation of
resistance with concentration is very large at low concentrations.
Therefore, quantitative estimation of CuSo4 is possible upto 0.4 normal. It is
more sensitive upto 0.1N CuSo4.
At high concentrations quantitative estimation may be done by titration
methods.
After addition of Barium chloride , a part of So4
2+ ions are precipitated
which do not contribute to the conductivity of the solution. A drop in
resistance is observed. It confirms the presence of So4
2+ ions.
Results and discussions
49. CuSo4 + BaCl2 CuCl2 + BaSo4(s)
The above given equation is the reaction taking place in our sensor after the
addition of BaCl2.
The general molecular weight balance is given by:
CuSo4 + BaCl2 CuCl2 + BaSo4(s)(precipiatate)
(159.6) + (208.2) (134.45) + (233.43)
(367.8) = (367.8)
0.0726 g + 0.0947g (needed for complete precipitation of the sulphate ion)
+ 0.061 (provided)
0.0467g of CuSo4 is precipitated and 0.0259g is left unreacted. To further
decrease the resistance more BaCl2 may be added.
Results and discussions
50. A paper sensor was developed for the detection of chemicals. It is based on the variation of
conductance (inverse of resistance) with concentration of the chemical present in aqueous
solutions.
It also uses measures the variation in resistance after precipitating some of the sulphate
ions. From the present study the following conclusions can be drawn.
It is possible to use soft paper to hold the liquid and allow the chemical species to diffuse
over the entire surface within 30 sec.
With increasing concentration of chemical species the resistance between the two ends of
the sensor decreases upto 0.4N CuSO4. Beyond this the change is not meaningful. However,
in view of the desired range of measurement being at low concentration only, it does not
pose any problem.
Known amounts of BaCl2 solution is added to precipitate sulphate ions. The resistance
further is due to increased concentration of chlorides and barium ions.
Conclusions
51. The findings of the present work are encouraging and may be
extended in the following direction:
The sensor should be tested with other ions also.
More studies are required to study the interaction between
different ions.
Calculation procedure for quantitative estimation should be
developed.
Future work
52. References
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[3] http://www.uv.es/positive/loc.html
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