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Introduction of Electrochemistry (電化學簡介) Electrochemical technique is a type of bio-sensing method.
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Basis of Electrochemistry
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Entropy (S) Entropy (S) Definition of Entropy: the amount of randomness, or molecular disorder, in a system. Example: icewater steam ice water steam Less disorder ---------------> More disorder Lower entropy -------------> Higher entropy
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Entropy change (∆S) Entropy change (∆S) ∆S = S final - S initial 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 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).
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Gibbs Free-Energy Change (∆G) ∆G = ∆H - T ∆S 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 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
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Chemical Reactions
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Example of a spontaneous reaction Glucose+O 2 Gluconic acid+H 2 O 2 GOX: Glucose Enzyme Example of a non-spontaneous reaction H 2 O 2 O 2 +2H + +2 e - 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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Role of Enzyme in Chemical Reactions
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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.
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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 Gluconic acid Glucose oxidase (ox) Glucose oxidase (red) O2O2 H2O2H2O2 e-e- Analyte, Biocatalyst, and Product
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Electrochemical Cell Transducer
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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。
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Display Display Cyclic Voltammetry (CV) Voltage Scan rate (V/s) cycle Redox couple
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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
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受測溶液 : H 2 O 2 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
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電化學 電路區塊圖 RS-232 指令和訊號 傳輸系統 CEREWE 電解槽 Communications of Command and Signal
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GUI and Display
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Product Examples of Electrochemical Biosensor
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Measurement of glucose in blood using an enzyme assay Glucose Meter Glucose Measurement
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Commercial Glucose Meter
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