Study of threshold-voltage Adjustable EG-FET as biosensor
|關鍵字:||臨界電壓;汲極源極控制法;反向器;pH緩衝溶液即時量測;鏈梅親和素即時量測;threshold voltage;VDS control method;inverter;pH beffer real-time measurement;Streptavidin real-time measurement|
|摘要:||生醫感測在微量分析物的研究在十幾年來已有長足的發展，無論是光學、電學及其相關領域，其中場效應電晶體(FET)也有廣泛應用。近年來，離子敏場效電晶體以及延伸式閘極場效電晶體也應用於生醫感測的研究，但是一般商業用FET在閘極電壓接地時都是處於off的狀態以節省電力的耗損，這些元件在用來進行即時(real-time)生醫感測卻是不方便的，因為參考電極不接地去調控電流(ID)可能會造成量測環境的不穩定，甚至於會出現電化學反應。為了改良量測環境，使用汲極源極控制法(VDS control method)來精準地控制元件臨界電壓(threshold voltage)所在的位置。
我們使用汲極源極控制法(VDS control method)應用於pH緩衝溶液的即時量測，同時比較參考電極是否接地以及是否修飾自組裝單分子層(SAM，self-assembled monolayer)對於量測穩定度的比較。實驗的結果看來，使用汲極源極控制法，讓參考電極接地以及表面修飾單分子層改良時漂效應(drift effect)、遲滯效應(hysteresis effect)。為了防止源極以及汲極電壓過大對基板產生漏電以及閘極端的靜電轟擊損壞FET元件，加入了一個反向器(inverter)，利用偏移電壓(offset)調控臨界電壓，並用此方法進行Streptavidin之即時量測實驗，亦能有對濃度進行分辨，量測極限可達到42 pM。|
Recently, real-time measurement in FET biosensor has been studied widely to detect and distinguish analyte in concentration instantly. To avoid unexpected chemical reaction and to provide a reference potential, the reference electrode in solution is kept grounded during experiment. However, under the real-time measurement, the characteristic of commercial FET devices are not suitable due to grounded reference electrode. Besides, the circumstance of device is disrupted by drift effect and hysteresis effect. Drift effect often occurs with construction and reconstruction of electric double layer and hysteresis effect happens with diffusion velocity of different ions in solution and competition of pKa of functional groups (-OH or -NH2 group) on the sensing chip. In this study, we investigated two method, VDS control method and inverter control method to stabilize the circumstance of solution under measurement. We regulated voltage of drain and source and kept gate electrode grounded to adjust the threshold voltage and setpoint. Moreover, inverter control method is designed to source grounded to stabilize FET device. In pH buffer measurement, drift effect and hysteresis effect were improved using VDS control method compared with conventional method. And the results showed that SAM can also stabilize the surface of sensing chip. In streptavidin measurement, concentration of streptavidin can be distinguished by surface potential change, and the limit of detection (LOD) is ~42 pM by using inverter control method. According to the results of our experiment, we believe that this technique can be applied to the future bio-sensing.
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