智慧型伏安系統設計與其碳纖維電極製作最佳化

Design of an Intelligent Voltammetric System and Fabrication Optimisation of Its Carbon Fiber Electrode

鄭青境(Ching-Ching Cheng)

指導教授 ： 楊明興

國立成功大學/電機資訊學院/電機工程學系碩博士班/博士(2003年)

https://doi.org/10.6844/NCKU.2003.00001

摘要

電化學伏安法常被用來量測可以氧化還原的微量物質。目前伏安法已被廣泛地應用於物理、化學、生物學、醫學與其他相關的領域。在本論文中，我們設計了一套由個人電腦 (PC) 與數位化伏安儀 (voltammeter) 組合而成的智慧型伏安系統。數位化伏安儀的硬體設計，係採用 VXIbus 擴展架構，整體電路包含系統控制電路板，伏安法量測電路板與電極評選電路板等。智慧型伏安系統可以用於高階、綜合或多樣化需求的伏安法實驗、並且具備儲存、分析與顯示等伏安法實驗結果的常用功能。數位化伏安儀除了可以提供單機 (stand-alone) 操作外，也可以藉由串列傳輸界面與 PC 連線，執行 Labview 圖控語言設計的伏安法功能與其他應用，譬如：自動搜尋氧化電位、量測結果的處理分析、儲存容量的擴充、伏安法任意波形的產生、新伏安法實驗以及其他附加功能等。

　　伏安儀電路具有電子抹除可規劃式唯讀記憶體 (EEPROM)，可以用來儲存各種波形參數與實驗資料，及寫入從 PC 下載的機器碼來更新伏安儀的程式；並且具有電極評選電路，可以量測電極的等效電阻與等效電容來評選電極的良窳。測試結果顯示，使用碳纖維電極在生理食鹽水 (PBS) 溶液中量測多巴胺 (dopamine，神經元間傳遞訊息的化學物質) 濃度時，伏安儀的最小氧化電流可以量測到 (或更低於) 10 pA (10-12 安培)，最小多巴胺濃度可以量測到 (或更低於) 10 ppb (10-12 分率)。伏安儀與 PC 的結合提供了快速、精確，自動化與多用途的能力。而在 VXIbus 架構下設計的伏安儀電路，也預留了硬體容易擴充的功能。

　　本論文也在智慧型伏安系統中設計了一套自動檢測程式，程式中應用田口玄一 (Taguchi) 博士提出的田口式品質工程方法來自動導引實驗，以推求出一組最佳微分常規脈波伏安法 (DNPV) 的實驗參數。本研究所進行的田口實驗為使用碳纖維電極量測生理食鹽水溶液中的多巴胺濃度。實驗結果顯示，我們僅需要使用一支電極與執行一組田口矩陣實驗的單電極單次測試方法來進行自動檢測，即可獲得最佳參數組合。從理論與實驗上顯示，田口式自動檢測伏安波形參數方法為一快速、準確與簡單的方法，可以消除採用試誤法 (trial-and-error) 的時間耗損與不佳參數值的設定。程式中也含有一套電極在實驗期間靈敏度衰減的補償方法。

　　使用碳纖維電極以電化學伏安法來量測微量物質是量測神經遞質 (neurotransmitter) 的重要方法之一。以往碳纖維電極的製作，沒有固定、標準的製程，以致不良率太高。在電極製作的材料與製程中，須要設定一些參數條件，實驗人員往往使用傳統的試誤法去找出較適用的參數，常耗費許多時間與成本，又不見得可以獲得良好的電極品質。本研究也應用田口方法來推求一組製作碳纖維電極的最佳參數與最適的製程。依照田口方法的實驗導引，我們採用靈敏度作為電極的主要品質特性，電極的靈敏度即為使用伏安法量測電極時測得的反應電流大小。在執行田口矩陣實驗而求得最適參數之後，我們依求得的最適條件製作十支碳纖維電極來驗證電極製程改善後的再現性，實驗結果顯示其平均信號雜音比 (S/N ratio) 為 29.7 db，由原製程的 22 db 提昇至約 30 db。此田口實驗的最適參數結果如下：碳纖維在微破璃管的管外長度為 0.3 mm；管內長度為 2.5 mm；電極的電化學前處理為將電極浸入生理食鹽水溶液中，施以 2.9 V 三角波，進行處理 15 秒；電極的 Nafion (全氟磺酸離子交換樹脂) 電鍍處理為將電極浸入 5% Nafion 溶液中，施以 2.6 V 直流電壓，進行處理 45 秒。

　　本論文實驗結果顯示，在智慧型伏安系統中應用田口方法來推求 DNPV 的最佳參數，可以降低 DNPV 實驗的材料成本，實驗時間，改善伏安法的實驗品質與人為誤差。碳纖維電極的製作最佳化方面，也同樣可以降低材料成本、實驗時間與提高碳纖維電極品質。

關鍵字

碳纖維電極 ； 靈敏度 ； 微分常規脈波伏安法 ； 多巴胺 ； 神經遞質 ； 田口方法 ； 伏安法

並列摘要

Electrochemical voltammetry is a common method for measuring and analysing redox reactions. Voltammetric techniques have been used in a wide range of chemical, physical, biological, medical and other applications. This dissertation presents an intelligent voltammetric system consisting of two units, a generic personal computer and a novel digital voltammeter with VXIbus (VMEbus extensions for instrumentation) architecture of system control board, voltammetric measurement board and electrode evaluation board. System is designed to provide superior, comprehensive, versatile and convenient storage, analysis and display of electrochemical and voltammetric waveforms. Voltammeter is capable of executing stand-alone operation or direct PC control through a Labview program and serial communication interface. PC connection gives additional functions such as automatic scanning of oxidation potential, expanded storage and processing of experimental data, arbitrary voltammetric waveform, etc.

　　In a stand-alone voltammeter, the system control circuit uses EEPROM (electrically erasable programmable read only memory) to store waveform parameters, experimental data and machine code program downloaded from PC. Electrode evaluation circuit can test electrode quality by measuring electrode equivalent resistance and capacitance. Voltammeter test results using carbon fiber electrode to measure the dopamine (a neurotransmitter) concentration in PBS (phosphate buffered saline) solution are presented. It shows that the minimum oxidation current can be measured to less than 10 pA, with a minimum detectable bulk concentration of less than 10 ppb (parts per billion). The combination of a PC with a stand-alone voltammeter offers high-speed, precision, automation, versatility and portability, while the VXIbus architecture allows easy expansion capability.

　　This dissertation also presents a procedure for autodetection of optimal DNPV (Differential Normal Pulse Voltammetry) parameters using the Taguchi quality engineering method in the proposed voltammetric system. We test the Taguchi experiment by using carbon fiber electrode to measure the dopamine concentration in PBS solution. From experimental results, we conclude that the one-electrode-single-test method using only one electrode and performing only one DNPV orthogonal array is preferred. It is shown both theoretically and experimentally that Taguchi-based autodetection of voltammetric waveform parameters is rapid, accurate and virtually foolproof, thereby eliminating the time-consuming and error-prone trial-and-error parameter set up of contemporary procedures. A method for offsetting decline of electrode sensitivity during extended experimentation is also presented.

　　Voltammetry using a carbon fiber electrode is one of the most important methods for measuring neurotransmitter. There has been no fixed or standard procedure for fabricating carbon fiber electrodes. Traditionally, the trial-and-error method has been used. Production yield has thus been inconsistent in quality and of low and variable quantity. In this dissertation, we also describe an optimised procedure for fabricating carbon fiber electrodes using Taguchi method (TM). Sensitivity, as determined by voltammetric measurement, is selected as the main quality characteristic of the carbon fiber electrode. After completing Taguchi experiment, ten carbon fiber electrodes were assembled according to the optimal parameters to check the reproducibility of the improved electrode fabrication. Experimental tests of the ten electrodes yielded an average S/N (signal-to-noise) ratio of about 29.7 db (decibel), showing a S/N ratio improvement from 22 to 30 db. The optimised parameter obtained is that using a glass micropipette (0.3 mm outer/2.5 mm inner length of carbon fiber) dipped into PBS solution under 2.9 V triangle-wave electrochemical processing for 15 s, followed by coating treatment of micropipette on 2.6 V DC for 45 s in 5% Nafion (perfluorinated anode ion-exchange resin) solution.

　　It thus shows that using Taguchi process optimisation in our intelligent voltammetric system can reduce the cost, shorten the experimental time, improve quality of voltammetric results, and avoid human error at same time. Fabrication optimisation of carbon fiber electrode can also dramatically improve cost, time and quality of carbon fiber electrode.

並列關鍵字

Carbon fiber electrode ； Sensitivity ； DNPV ； Dopamine ； Neurotransmitter ； Taguchi method ； Voltammetry

參考文獻

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