固態接觸離子選擇電極感測性能衰退與改進策略之研究

Abstract

固態接觸式離子選擇電極(Solid-contact ion-selective electrode, SCISE)近年來已大量被整合於可攜式感測器或穿戴式裝置上，並且應用於各項長期連續感測的領域中。然而，本研究觀察到固態接觸式離子選擇電極於此長期感測的應用上，會逐漸出現感測性能劣化之行為，其中包含了電極感測靈敏度的衰退與電位訊號中60 Hz環境雜訊增強的現象。因此，透過分析固態接觸式離子選擇電極與其各層材料於長期感測環境條件下的電化學阻抗變化，可以推測其劣化的原因來自於離子選擇薄膜中電化學活性物質的溶出(Leaching)或者於電極中產生水層而造成之效應。針對此原因，本研究使用了不同種類的塑化劑於PVC離子選擇薄膜(Ion-selective membrane, ISM)的製備中，進而比較其塑化劑對於固態接觸式離子選擇電極的感測靈敏度衰退速率造成之影響。其中，本研究指出在塑化劑分子量最大的DOS電極組別中，其電極感測靈敏度在連續感測一週後仍可以維持在理論值的±5 %之內。另外，除了透過材料選擇方面來改善固態接觸式離子選擇電極的感測性能劣化行為，本研究建製了一可編程增益儀表放大器(Programmable-gain instrumental amplifier, PGIA)，透過增益放大來補償電極衰退之靈敏度；並且搭配雙T帶斥濾波器(Twin T notch filter)來抑制電位訊號中60 Hz環境雜訊，以提升所量測離子濃度之精確度。透過硬體方面的改善策略，可以使電極在連續感測一週的情況下，仍維持其初始的感測表現。除此之外，本研究透過固態接觸式鉀離子選擇電極對於作為干擾離子的銨離子之選擇係數，建構一檢量線來校正所感測到的目標鉀離子濃度，以增加此電極之感測準確度。最後，希望通過上述改善策略，讓本研究所建構之離子感測器達到性能的最佳化。

Solid-contact ion-selective electrodes (SCISEs) have been widely integrated into portable sensors or wearable devices in recent years, applied in various fields requiring long-term continuous monitoring. However, this study observes that SCISEs exhibit gradual degradation in sensor performance during long-term continuous sensing, including the sensitivity decline of SCISE and an increase in 60 Hz noise in the sensing signal. Therefore, by analyzing the electrochemical impedance changes of SCISEs and the layers under long-term sensing conditions, it is inferred that the degradation may be due to the leaching of electrochemically active species from the ion-selective membrane or effects induced by water layer formation within the electrode. To address these issues, this study uses different types of plasticizers in the PVC-base ion-selective membrane in order to compare the effect on the rate of the sensitivity decline in SCISEs. The study describes that SCISEs using the plasticizer with the highest molecular weight, DOS, can maintain electrode sensitivity within ±5% of the theoretical value after continuous sensing for one week. In addition to improving the sensing performance of SCISEs through material aspect, this study develops a programmable-gain instrumental amplifier (PGIA) to compensate for sensitivity decline through the gain amplification. A twin T notch filter is also employed to suppress 60 Hz environmental noise in the sensing signal, enhancing the precision of measured ion concentrations. Furthermore, this study uses the selectivity coefficient of "K" ^+-SCISE for interfering ions, 〖"NH" 〗_"4" ^+, to construct a calibration curve. This curve is used to enhancing the accuracy of the measured "K" ^+ concentrations, thereby. Ultimately, through these improvement strategies, this study aims to optimize the performance of the ion sensor in this research.