以奈米矽線場效應電晶體檢測中性分子與離子濃度

Abstract

首先，我們提出一項以奈米矽線場效應電晶體為基礎來偵測離子溶液環境中非極性以及電中性分子的技術，此技術原理是基於分子交互作用後電容會改變的特性，當奈米線表面發生分子交互作用便會改變表面分子的電容，此一改變會反映在奈米線交流阻抗的振幅大小與相位，搭配數值計算我們可以從振幅大小及相位的變化推測此分子交互作用中電場與電容何者的改變較為顯著。實驗上我們用不同帶電極性以及電中性的組胺酸對這項技術進行驗證，我們證明了不論帶正負電還是不帶電，組胺酸都可以成功的被偵測，而偵測中性組胺酸的靈敏度更高達到10-12莫爾/公升。我們更進一步證明此技術可以運用在非極性己烷分子的偵測，除此之外，此技術也成功證明可以應用在表面沒有絕緣層的奈米線。 接下來利用雙閘極奈米矽線電晶體為架構，因其二氧化矽絕緣層在緩衝溶液中會水解進而進行質子化與去質子化而形成帶電的表面，造就了一個研究帶電表面與離子交互作用的平台。首先，我們以放入金屬電極的離子溶液中做為液態閘極，此液態閘極與背閘極都有控制電晶體的功能，藉著量測「電流-液態閘極電壓」與「電流-背閘極電壓」的曲線我們可以對兩個閘極的功效做評估，研究中得到本系統液態閘極的作用能力比背閘極強21.8倍。除此之外，改變緩衝溶液的離子濃度我們發現電流-閘極電壓呈現水平偏移，而此偏移量與溶液濃度的對數呈線性相關，我們藉此證明此系統可以成為離子濃度定量的工具。進一步比較「電流-液態閘極電壓」與「電流-背閘極電壓」的曲線，我們在重合時發現兩者之間在不同濃度底下有不同的修正量，進一步分析發現此修正量與德拜長度有關，這也提供了另一種濃度定量的方法。

First, we report on a technique that can extend the use of nanowire sensors to the detection of interactions involving nonpolar and neutral molecules in ionic solution environment. This technique makes use of the fact that molecular interactions result in a change in the capacitance of the involving molecules. For the interactions taking place at the surface of nanowires, this capacitance change can be determined from the analysis of the measured nanowire complex impedance. To demonstrate this technique, histidine with different charge polarities controlled by the solutions pH value was detected, including the detection of electrically neutral histidine at a sensitivity of 1 pM. Furthermore, it is shown that nonpolar molecules, such as hexane, can also be detected. The technique is applicable to the use of nanowires with and without surface insulating oxide. We show that the information about the changes in the amplitude and phase of the complex impedance reveals the fundamental characteristics of the molecular interactions, including the electric field and the capacitance. Next, we demonstrate a method that can quantitatively determinate the ionic strength of the electrolyte solution using dual-gated Si nanowire field effect transistor (SiNW-FET) without the need of reference electrode. Shifts of current-backgate voltage (I-Vbg) character measured using FET reveals the information about the sum of potentials that arise from the liquid gate-electrolyte interface and distribution of ions at electrolyte-SiO2 interfaces, allowing quantitative determination of ion strength. Comparing I-Vbg with current-liquid gate voltage (I-Vlg), it’s shown the liquid gate is more effective than the backgate by a factor of 21.8. Also, an extra offset voltage which is proportional to the Debye length was observed, providing another approach to quantitatively acquire the ionic strength.