利用奈米孔道檢測水溶液環境中痕量金屬離子濃度的理論模型分析

Abstract

奈米流體裝置具有高度的應用潛力，目前已在發展中的應用有: 離子電流整流、壓差發電、濃鹽差發電、奈米孔道之海水淡化(除鹽)以及金屬離子檢測等應用。在本篇當中吾人將展示離子電流整流和金屬離子檢測及其機制的探討。 在第一章節中，吾人利用p-tert-butylcalix[4]arene crown將聚對苯二甲酸乙二酯的錐形奈米孔道進行表面改質，以理論模擬透過離子電流整流的特性，檢測銫離子在水溶液環境中的痕量濃度。其中吾人針對表面改質長度以及奈米孔道的半角等因素於奈米孔道在檢測上的影響。由線性迴歸分析整流比(Rf =|I(-1 V)|/|I(+1 V)|)與銫離子濃度的關係，可得知當改質長度1000奈米和奈米孔道的半角為1°時會有最佳的檢測效果，其最大的檢測範圍為[0.3 nM, 500 nM]，檢測極限為0.3 nM。此檢測極限相比常用的分析工具，如原子吸收光譜、光電化學傳感器等還要更靈敏。 在第二章節中，吾人利用表面以單寧酸改質的子彈型孔道檢測以銅離子為目標離子，鐵離子為雜質離子(反之亦然)，鉀離子為背景離子進行檢測。其中吾人針對這三種離子跟單寧酸的吸附反應其反應級數對於奈米孔道離子電流整流的影響。吾人展示在背景電解質濃度為1, 10, 100以及1000 mM時，當背景電解質濃度為1mM時由於電雙層重疊的現象較顯著，使其有最佳的檢測效果。銅離子和鐵離子的最佳檢測範圍分別為[0.5 μM, 1000 μM] 和 [1 nM, 1000 nM]。兩者的檢測極限都較傳統的檢測儀器來得更加靈敏，因此以奈米孔道做為檢測方法之一為更加的選擇。

Nanofluidic device is capable of many usage including ionic current rectification (ICR), pressure driven energy conservation, desalination, salinity gradient power generation and metal ion detection. Among these, we perform two applications: ion current rectification and metal ion detection; and the underlying mechanism is investigated. In chapter 1, a conical polyethylene terephthalate nanopore surface modified with p-tert-butylcalix[4]arene crown is adopted to model theoretically the detection of a trace concentration of cesium ions in an aqueous environment through its ion current rectification (ICR) behavior. In particular, the background salt, the modification length of the modified layer and the half cone angle of the nanopore are examined for their influence on the performance of the nanopore, measured by its ICR factor. The results of regression analysis for the dependence of the ICR ratio on the concentration of cesium ions suggest that the optimum performance can be achieved by choosing a modified layer length of 1000 nm and half cone angle of 1°, where the widest detection range is [0.3 nM, 500 nM] and the lowest detection limit is 0.3 nM. This detection limit is lower than that of the commonly used analytical tools such as atomic absorption spectroscopy, optical chemosensors, and electrochemical sensors. In chapter 2, we adopt a bullet-shaped nanopore surface modified with tannic acid as an example, the detection of a trace concentrations of Cu2+ (target ion) when Fe3+ (impurity) is present with K+ as background ions under various conditions is simulated. In particular, the influence of the reaction order of the association of target ions and tannic acid on the nanopore performance is examined. We show that the lower the background concentration the better the detection performance. For the examined background concentrations of 1, 10, 100, and 1000 mM, the optimal detection ranges are [0.5 μM, 1000 μM] and [1 nM, 1000 nM] for Cu2+ and Fe3+, respectively. The detection limits, 0.5 μM for Cu2+ and 1 nM for Fe3+, are lower than those retrivable from conventional instruments, suggesting the potential of applying the present nanopore based approach.