酚類感測之電化學法的研究

Study on Phenols Sensing by Electrochemical Methods

陳柏中(Po-Chung Chen)

指導教授 ： 鄭宗記

國立臺灣大學/生物資源暨農學院/生物產業機電工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.02918

摘要

本論文的研究是以發展適用於酚類感測的電化學技術為核心，將其應用於茶品工業的分類和品管以及酚類汙染物感測上，並開發新穎微尺度的電沉積局部固定化酵素技術，以利未來新型酚類生物感測器的發展。
本論文之各部分研究摘要如下:
一、以茶品萃取液的氧化還原電位作為評估茶品醱酵程度的指標
茶品萃取液的氧化還原電位被建議作為茶品醱酵程度的電化學指標，其氧化還原電位係利用高輸入阻抗(>1000 GΩ)電位計對白金電極和Ag/AgCl參考電極進行量測，並利用赤/黃血鹽標準氧化還原對驗證氧化還原電位量測的信賴性。單寧酸濃度和抗壞血酸對於單寧酸氧化還原電位的影響被分別探討。茶葉的室內萎凋醱酵過程，氧化還原電位與醱酵時間表現出高度的關聯性。不同醱酵程度的茶葉，如煎茶、碧螺春、台灣烏龍茶、立頓綠茶、立頓紅茶和台灣紅茶，其氧化還原電位被探討比較。
二、以赤血鹽對單寧酸預氧化開發定量茶品中單寧濃度之定電位式流動分析系統
本研究提出利用赤血鹽對單寧酸預氧化策略，有效地避免直接電氧化單寧造成的電極汙染問題，應用於開發茶單寧定量的定電位式流動分析系統。工作電壓與流率對於量測系統的影響被討探(最佳量測條件: 工作電壓: -0.1 V vs. Ag/AgCl ; 流率: 2.28 mL min-1)。系統對單寧酸的線性檢量範圍可利用不同濃度的赤血鹽(1 mM和10 mM)進行調控(其檢量線分別為10-50 μg mL-1和100-500 μg mL-1)。本研究所提出的方法與Folin-Ciocalteau method和the ferrous tartrate method進行比對驗證，有高度的正相關(r = 0.9808; r = 0.9899)。不同醱酵程度茶的單寧酸濃度被量測。
三、以黃血鹽基質循環增幅法於固定化酪胺酸酶定電位式流動分析系統定量鄰苯
二酚、苯酚、雙酚A
本研究提出利用酪胺酸酶(EC 1.14.18.1)催化酚類反應的線上流動分析酚類生物感測系統。固定化酪胺酸酶反應器係利用controlled pore-size aminopropoyl glass beads 作為固定化基質，裝填至流動分析系統的管路中。檢測電流可利用10 mM 黃血鹽 (溶於pH 7.0, 10 mM 磷酸緩衝液)與酪胺酸酶催化酚類氧化反應形成基質循環增幅檢出訊號，鄰苯二酚、苯酚的檢測極限可以被增幅100 倍，而濃度為2.5 ×10-6M 雙酚A 可被檢出(S/N>3; 工作電壓: +0 V vs. Ag/AgCl; 流率: 1.0 mL min−1)。
四、局部電沉積幾丁聚醣方法開發與固定化酵素之應用
本研究利用電極對間所產生pH 梯度的電化學現象，分別嘗試以掃描式電化學顯微鏡(Scanning electrochemical microscope, SECM) 的direct mode 與微流道局部電沉積幾丁聚醣於導體基材表面。利用SECM direct mode (對極: Pt 微電極;工作電極: 平板Au 基質電極)與脈衝電壓(1 s, -1.0 V vs. Ag/AgCl)，可造成局部的pH 梯度，直接沉積直徑為數百微米幾丁聚醣於基質電極上，並藉由於不同位置上依序地電沉積形成幾丁聚醣沉積陣列; 另一策略利用微流道限制幾丁聚醣的流動並電沉積(10 min, -3.0V Au substrate vs. Pt wires)，可形成微尺度的幾丁聚醣帶狀圖案(line width = 100 μm)。其沉積層表面的胺基係利用NHS-fluorescein 與其反應，於共軛焦雷射掃描式顯微鏡下進行觀察。相較於使用SECM direct mode，利用微流道電沉積幾丁聚醣，其沉積層較具重複性且可產生被定義的圖案。二方法皆可於電沉積幾丁聚醣的過程同時包埋葡萄糖氧化酵素， 其活性利用SECM generation-collection mode 觀察，使用微流道的固定化酵素活性分布較為均一，而其表面粗糙度則利用非接觸式原子力顯微鏡觀察。

關鍵字

茶品氧化還原電位 ； 赤血鹽對單寧預氧化 ； 黃血鹽基質循環增幅 ； 局部電沉積幾丁聚醣

並列摘要

Novel electrochemical sensing methods for phenolic compounds have been developed for the quality control in tea industry (Part 1 & 2) and for the detection of phenolic pollutants based on substrate recycling amplification strategy (Part 3). Electrodeposition techniques of proteins on a charged bio-matrix were designed to immobilize analytical enzymes on a micro-pattern (Part 4), localized substrate recycling amplification may be investigated on the micro-fabricated bio-patterns.
Part 1: Redox potential of tea infusion as an index for the degree of fermentation Redox potential of tea infusion was suggested as a working index for estimating the extent of tea fermentation. The redox potential of tea infusion was measured between platinum and Ag/AgCl electrode pair with a voltmeter with a high input impedance (>1000 GΩ). The reliability of redox potential measurement was verified with a standard redox couple, ferricyanide / ferrocyanide. Effect of tannic acid concentration and ascorbic acid to the redox potential of tannic acid were discussed. Redox potential showed a high correlation with the fermentation degree and the indoor withering time (fermentation time). Several kinds of tea with different fermentation extents including Japanese Sencha (unfermented), Chinese Pilochun (slightly fermented), Taiwanese Pouchong (mild fermented), Taiwanese Oolong (partial-fermented), Western black tea (fully fermented) were measured and compared.
Part 2: Determining the levels of tannin in tea by ferricyanide pre-reaction in an amperometric flow-injection system
An amperometric flow-injection assay for tea tannin was proposed, which was based on ferricyanide pre-oxidation to prevent the electrode fouling problems frequently encountered in oxidation of phenolic compounds. The working potential and flow rate were optimized to be -0.1 V vs. Ag/AgCl and 2.28 mL min-1, respectively. The linear dynamic range of tannic acid (10-50 μg mL-1 and 100-500 μg mL-1) can be adjusted using 1 mM and 10 mM ferricyanide, respectively. The proposed method was verified with Folin-Ciocalteau method (r = 0.9808), and the ferrous tartrate method (r = 0.9899). Tea with various fermentation degrees were successfully measured with a sample throughput of 15 samples h−1.
Part 3: Amperometric flow-injection determination of catechol, phenol and bisphenol A by ferrocyanide substrate recycling amplification within an immobilized tyronsianse
An on-line phenols sensing flow-injection analysis (FIA) system was proposed, which was based on the broad phenolic oxidation capacity of mushroom tyrosinase (EC 1.14.18.1). The enzyme was densely immobilized on controlled pore-size aminopropoyl glass beads packed within a mini-reactor, and the reactor was installed in the flow stream of an amperometric FIA system. By reacting with 10 mM ferrocyanide (in pH 7.0, 10 mM phosphate buffer) supplied from the side stream of the flow system, substrate recycling amplification was conducted to regenerate the reduced phenols for the subsequent oxidation process catalyzed by the immobilized tyrosinase. The signals of catechol and phenol were amplified 100 fold; bisphenol A, an important endocrine distruptor, can be detected at 2.5 ×10-6 M (S/N>3; working potential: +0 V vs. Ag/AgCl; flow rate: 1.0 mL min−1).
Part 4: Localized Electrodeposition of Chitosan as Matrix for Enzyme Immobilization
Based on the pH gradient electrochemically generated between electrodes, two localized chitosan electrodeposition methods were developed by either scanning electrochemical microscope (SECM) direct mode or microfluidic electrodeposition. With SECM direct mode, a localized pH gradient was induced between planar Au working electrode (the substrate) and the Pt auxiliary microelectrode by potential pulses (1 s, 1.0 V vs. Ag/AgCl). An array of chitosan spots with hundreds of µm in diameter can be directly deposited on the Au substrate sequentially. The procedure could be carried out within a microfluidic channel in order to restrict the spreading of chitosan solution. Chitosan was gradually deposited (10 min, 3.0V Au substrate vs. Pt wires) along the channels with defined micro-scaled geometry (line width = 100 µm). The surface amino groups labeled with NHS-fluorescein were observed with confocal laser scanning microscopy. The deposition method using microchannels demonstrated a more reproducible and well-defined surface. Both methods can also be used to entrap glucose oxidase (GOx) during the deposition process. SECM in the generation-collection mode was used to detect the activity of GOx within the chitosan micro-patterns by oxidation of the formed hydrogen peroxide. The activity distribution of the immobilized GOx on the deposited chitosan layer was more uniform with the microfludic channel method as compared to that obtained by SECM direct mode. The roughness was investigated with non-contact atomic force microscopy.

並列關鍵字

redox potential of tea infusions ； tannin pre-reaction with ferricyanide ； ferrocyanide substrate recycling amplification ； localized electrodeposition of chitosan

參考文獻

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