electrochemical sensor 061102

7/23/2019 Electrochemical Sensor 061102

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Introduction of Electrochemistry

Electrochemical technique is a type of bio-sensing method.


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Basis of Electrochemistry


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Entropy (S)

Definition of Entropy:

the amount ofrandomness, or

molecular disorder, in a system.

Example:ice water steam

Less disorder ---------------> More disorder

Lower entropy -------------> Higher entropy


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Entropy change (S)

S = Sfinal

- Sinitial

If S is positive, the system has become more random.

If S is negative, the system has become less random.


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Spontaneity of Reaction

Reaction: a chemical or physical change

Two factors that determine thespontaneity (of a reaction in a system:

(1) a release or absorption of heat (H),

(2) an increase or decrease in molecular

randomness (S).


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Gibbs Free-Energy Change (G)

G = H - TS

Free-energy

change

Heat of

reaction

Temperature

Entropy

change

G > 0 Non-spontaneous reaction

G < 0 Spontaneous reaction


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Potential Energy

G = - n FE

G > 0 Non-spontaneous reaction

G < 0 Spontaneous reaction

G is free energy change.

E is applied voltage.

Fis Faraday constant

n is number of mole


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Chemical Reactions


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Example of a spontaneous reaction

Glucose+O2 Gluconic acid+H2O2

GOX: Glucose Enzyme

Example of a non-spontaneous reaction

H2O2 O2+2H++2e-

GOx

Potential

Examples of

Electrochemical Reactions


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Oxidation and Reduction

A + e-A-

A A+ + e-

Oxidation reaction

Reduction reaction


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ole of Enzyme in Chemical Reaction


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What is Biosensor?

A biosensor is normally defined as a device incorporating

a biological molecular recogni tion component connected to

a transducer which can output an electronic signal that is

proportional to the concentration of molecule being sensed.

Donal Leech, Chemical Society Reviews, 1994, 205-213.


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Components of Biosensor

a) Biocatalyst - converts the analyte into product.

b) Transducer - detects the occurrence of the reaction and converts it

into an electrical signal.c) Amplifier - amplifies the usually tiny signal to a useable level.

d) Microprocessor - signal is digitized and stored for further processing,

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


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Analytes vs. Recognition Elements


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Working electrode

Glucose

Gluconicacid

Glucose

oxidase (ox)

Glucose

oxidase (red)O2

H2O2

e-

Analyte, Biocatalyst, and Product


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Electrochemical Cell

Transducer


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Electrochemical Cell

Working electrode (WE) :

Reference electrode (AE) :

Counter electrode (CE): Cell

CEcell


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Display

Cyclic Voltammetry (CV) Voltage

Scan rate (V/s)

cycle

Redox couple


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CV

:

-1v ~ 1v

0.1 v/sec20


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: H2O2-1v ~ 1v

0.1 v/sec20

CV


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RS-232

CE RE WE

Communications of

Command and Signal


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GUI and Display


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Product Examples ofElectrochemical Biosensor


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Measurement of glucose in blood

using an enzyme assayGlucose Meter

Glucose Measurement


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Commercial Glucose Meter

electrochemical sensor 061102

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