Biosensors: By Partha Sarathi Tripathy Roll – 0301212360 Electrical Engineering

BIOSENSORS BY Partha Sarathi Tripathy ROLL – 0301212360 ELECTRICAL ENGINEERING 11/01/09

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Introduction 

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A Biosensor can be defined as a compact analytical device incorporating a biological or biologically derived sensing element either integrated within or intimately associated with a physicochemical transducer. The main aim of a biosensor is to produce either discrete or continuous digital electronic signals, which are proportional to a single analyte or a related group of analytes. In simple language it means that it is an analytical device, which converts a biological response into an electrical signal. 2

Properties of Biosensors : 

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The biological component must be specific and stable State the main ideas you’ll be talking about. The reaction should be as independent of physical parameters such as pH, temperature and stirring as possible . The response should be accurate, precise and reproducible . The sensing element should be tiny and biocompatible . The complete unit should be cheap and portable.

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Design Features of Biosensors :

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Biocatalyst - converts the analyte into product . Transducer - detects the occurrence of the reaction and converts it into an electrical signal . Amplifier - amplifies the usually tiny signal to a useable level. Microprocessor - signal is digitised and stored for further processing.

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Display - usually need a real-time display of the analyte concentration .

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Signal Transduction

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Biosensors can be classified by the method used to achieve signal transduction. They are: Amperometric biosensors Potentiometric biosensors Optical biosensors Calorimetric biosensors Piezo-electric biosensors 5

Amperometric

Biosensors 

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A potential is applied between the central platinum cathode and the annular silver anode which generates a current (I) proportional to the oxygen concentration ,which is carried between the electrodes by means of a saturated solution of KCl. This electrode compartment is separated from the biocatalyst i.e. GOD (glucose oxidase,) by a thin oxygen-permeable plastic membrane (e.g. Teflon) and the analyte solution is separated from the biocatalyst by another membrane, permeable to the substrates and products. 6

Potentiometric Biosensors : semipermeable membrane b) entrapped biocatalyst c) glass membrane of a pH-probe d) pH-probe e) electrical potential f) Ag/AgCl electrode g) dilute HCl a)

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reference electrode Potentiometric biosensors make use of ion-selective electrodes in order to transduce the biological reaction into an electrical signal. Such devices measure the release or consumption of ions during a reaction . 7

Optical Biosensors : There are two general approaches taken to implement optical biosensors: 

Measuring the change in light reflectance : here we measure the change in reflectance at a single wavelength of a dye as a result of a pH change or oxidation of the dye.Optical fibres are used to transmit light to and from the reflectance probe. This allows for miniaturisation of the sensor element.

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Measuring luminescence: This approach makes use of firefly luciferase to measure ATP. This technique is used to monitor any coupled enzyme that produces or uses ATP.

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Calorimetric Biosensors 

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The sample stream (a) passes through the outer insulated box (b) to the heat exchanger (c) within an aluminium block (d). From there, it flows past the reference thermistor (e) and into the packed bed bioreactor (f, 1ml volume), containing the biocatalyst, where the reaction occurs. The change in temperature is determined by the thermistor (g) and the solution passed to waste (h). External electronics (l) determines the difference in the resistance, and hence temperature, between the thermistors . 9

1.   Piezo-electric

Biosensors 

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For any piezo-electric crystal, the change in frequency is proportional to the mass of absorbed material. The frequency change can be easily detected by simple electronic circuits. The major drawback of these devices is the interference from atmospheric humidity and the difficulty in using them for the determination of material in solution. The advantage of this is that these are inexpensive, small and robust, and capable of giving a rapid response.

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CONCLUSION 

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With few exception,many of the technical approaches that are important to bioelectronics are today commercially unproven.So far bioelectronics has not proven a solid block in general engineering and technical field.Practically it does not have the vast use in general class of human society.It will be a great advantage if by using of bioelectronics of such functional neuronal arrays as a viable approach to fabricate “BRAIN COMPUTER”.The neurobiology and physics involved in neuronal dynamics and making computation.

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THANK YOU

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