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Introduction of Electrochemistry ( 電化學簡介). Electrochemical technique is a type of bio-sensing method. Basis of Electrochemistry. Entropy (S) Definition of Entropy : the amount of randomness , or molecular disorder , in a system. Example: ice water steam
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Introduction of Electrochemistry(電化學簡介) Electrochemical technique is a type of bio-sensing method.
Entropy (S) Definition of Entropy: the amount of randomness, or molecular disorder, in a system. Example: icewater steam Less disorder ---------------> More disorder Lower entropy -------------> Higher entropy
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.
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) ∆G = ∆H - T ∆S Free-energy change Entropy change Temperature Heat of reaction G > 0 Non-spontaneous reaction G < 0 Spontaneous reaction
Potential Energy G = - n F E G > 0 Non-spontaneous reaction G < 0 Spontaneous reaction G is free energy change. E is applied voltage. F is Faraday constant n is number of mole
Example of a spontaneous reaction Glucose+O2 Gluconic acid+H2O2 GOX: Glucose Enzyme Example of a non-spontaneous reaction H2O2 O2+2H++2e- Potential Examples ofElectrochemical Reactions GOx
Oxidation and Reduction Oxidation reaction A A+ + e- Reduction reaction A + e- A-
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.
Working electrode Glucose oxidase (ox) H2O2 Glucose e- Gluconic acid Glucose oxidase (red) O2 Analyte, Biocatalyst, and Product
Transducer Electrochemical Cell
Electrochemical 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。
DisplayCyclic Voltammetry (CV) • Voltage • Scan rate (V/s) • cycle Redox couple
CV訊號 例一 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
CV訊號 例二 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
RS-232 電化學 電路區塊圖 指令和訊號傳輸系統 電解槽 CE RE WE Communications of Command and Signal
Glucose Measurement Measurement of glucose in blood using an enzyme assay Glucose Meter