利用電流特性觀察微奈米濃縮晶片之作用機制及其應用

Abstract

本研究開發的微奈米流體濃縮晶片是利用微米流道與奈米流道製成，施加一 電位差於具有離子選擇性(ion-selective)的奈米流道兩端可產生濃度極化效應(ion concentration polarization, ICP)：於高電位處產生離子空乏區(ion depletion region)，於低電位處產生離子濃縮區(ion concentration region)。而後，施加一偏壓於空乏區可產生第二種電滲透流(electroosmosis of second kind)並於空乏區的高電位處會產生原濃度的105~106 倍的濃縮區塊(preconcentration plug)。此濃縮器(preconcentrator)為樣本前處理步驟的一環並可整合於微全分析系統(micro total analysis system, μTAS)，以大幅降低後端偵測的下限，達到低濃度生物標記(Biomarker)的偵測。 本文詳述微奈米流體濃縮晶片的設計與驗證流程: 濃縮晶片的流道設計與電路模擬、量測電路模擬所需參數、建立並驗證濃縮晶片的電阻模型以及驗證奈米流道具離子選擇性並求出啟動濃縮機制的最低操作電壓。 文獻中濃縮機制的啟動及濃縮區塊的行為多無法被預測與描述，因此本研究利用Labview架設迴路電流監測系統(loop currents monitoring system)描述離子於濃縮機制發生前後的現象:及時監測左、右迴路電流來判讀濃縮區塊出現的時間、位置以及濃縮區塊的行為模式。並利用迴路電流描述離子於濃縮機制發生後的電干擾現象、離子濃度與迴路電流的關係以及推導左右迴路電流不平均的電阻模型。其中，濃縮區塊的行為被歸類為以下四種模式：穩定濃縮模式(blocked mode)、濃縮區塊振盪模式(oscillation mode)、濃縮區塊突破強空乏區模式(burst mode)及濃縮區塊通過弱空乏區的離子槍模式(ion gun mode)。 本研究開發的迴路電流監測系統具有及時掌握濃縮機制啟動的時間以及濃縮區塊的行為模式與位置的能力，因此將來可採用免螢光標定(label-free)的檢體(analyte)、抗體(ligand)與試劑(reagent)等進行樣本預濃縮，以利後端的生物檢測。

In this thesis, a novel method,”loop currents monitoring”, was developed to interpret the onset of the preconcentration mechanism and the behaviors of a preconcentrated plug of a nanofluidic preconcentrator without fluorescent labeling. Initially, the design and validation methods and processes of nanofluidicpreconcentration chips were proposed starting from parameter setup, circuit simulations, developements and validations of resistive models, tests of ion-selective nanochannels to getting the lowest manipulation voltage of the onset of preconcentration mechanism. Four operational modes of a preconcentrated plug were observed during the preconcentration process and were explained by loop currents of the chip. The values of loop currents depended on how many counter-ions passing through cross-sectional areas of ion-selective nanochannels per second. The movements of the preconcentration plug and ion depletion region were described by flow profiles. Phenomena of uneven distribution of left and right loop currents and the relationship between gray values for fluorescent intensity of labeled proteins and magnitudes of loop currents after preconcentration mechanism happened were described in details. A resistive model after the preconcentration plug accured was constructed. In summary, the presented nanofluidic preconcentrator demonstrates multiple operational modes for a label-free protein preconcentration with the capability to precisely control and rapidly preconcentrate proteins. With the analysis of loop currents in our chip, various biological applications without fluorescent labeling could be demonstrated in the future.