Introduction of Electrochemistry （電化學簡介）

Electrochemical technique is a type of bio-sensing method.

Basis of Electrochemistry

Entropy Entropy (S)(S)

Definition of Entropy:the amount of randomness, or

molecular disorder, in a system.

Example: iceice water steamwater steamLess disorder ---------------> More disorderLower entropy -------------> Higher entropy

Entropy change Entropy change ((∆∆S)S)

∆S = Sfinal - Sinitial

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

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

Spontaneity of Reaction

Reaction: a chemical or physical change

Two factors that determine the spontaneity ( 自發性） of a reaction in a system:

(1) a release or absorption of heat (∆H), (2) an increase or decrease in molecular randomness (∆S).

Gibbs Free-Energy Change (∆G)Gibbs Free-Energy Change (∆G)

∆G = ∆H - T ∆S

Free-energychange

Heat ofreaction

Temperature

Entropychange

G > 0 Non-spontaneous reactionG > 0 Non-spontaneous reactionG < 0 Spontaneous reactionG < 0 Spontaneous reaction

Potential EnergyPotential Energy

G = - n F E

G > 0 Non-spontaneous reactionG < 0 Spontaneous reaction

G is free energy change.E is applied voltage. F is Faraday constant n is number of mole

Chemical Reactions

Example of a spontaneous reactionExample of a spontaneous reaction

Glucose+O2 Gluconic acid+H2O2

GOX: Glucose Enzyme

Example of a non-spontaneous reactionExample of a non-spontaneous reaction

H2O2 O2+2H++2e-

GOx

Potential

Examples ofElectrochemical Reactions

Oxidation and ReductionOxidation and Reduction

A + e- A-

A A+ + e- Oxidation reaction

Reduction reaction

Role of Enzyme in Chemical ReactionsRole of Enzyme in Chemical Reactions

What is Biosensor?

A biosensor is normally defined as a device incorporating

a biological molecular recognition 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.

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.

Analytes vs. Recognition ElementsAnalytes vs. Recognition Elements

Working electrode

Glucose

Gluconic acid

Glucose oxidase (ox)

Glucose oxidase (red)

O2

H2O2

e-

Analyte, Biocatalyst, and Product Analyte, Biocatalyst, and Product

Electrochemical Cell

TransducerTransducer

Electrochemical CellElectrochemical Cell

• Working electrode (WE) : 電化學反應進行的位置

• Reference electrode (AE) : 工作電極之電位參考點

• Counter electrode (CE): Cell 必須維持電中性，使用 CE維持 cell的電中性。

DisplayDisplay

Cyclic Voltammetry (CV)• Voltage

• Scan rate (V/s)

• cycle

Redox couple

CVCV 訊號 例訊號 例一一

受測溶液 : 黃血鹽掃描電位： -1v ~ 1v掃描速率： 0.1 v/sec掃描時間： 20秒

受測溶液 : H2O2掃描電位： -1v ~ 1v掃描速率： 0.1 v/sec掃描時間： 20秒

CVCV 訊號 例訊號 例二二

電化學

電路區塊圖

RS-232指令和訊號傳輸系統

CE RE WE

電解槽

Communications of Communications of Command and SignalCommand and Signal

GUI and DisplayGUI and Display

Product Examples of Electrochemical Biosensor

Measurement of glucose in blood using an enzyme assay

Glucose Meter

Glucose Measurement

Commercial Glucose Meter