多晶矽奈米線場效電晶體於生物感測上的應用

Abstract

本研究運用一個簡單和低價的半導體製程技術來製作多晶矽奈米線場效電晶體，並成功的證實可應用於生物感測上。此研究中的奈米線場效電晶體是藉由整合現今半導體製程技術中的sidewall spacer technique所製作出來，此方式捨棄以往昂貴的E-beam lithography 製程。此外我們發現多晶矽奈米線在水中的電性跟單晶矽非常相似，推測此現象為水中的氫離子或氫氧根離子修飾多晶矽奈米線表面缺陷所造成的電性改善現象。在本實驗的初步測試上，biotin-avidin/streptavidin 和 boronic acid/dopamine 分別被用於證明多晶矽奈米線在生物體和化學樣品上的感測能力。當奈米線表面分別經過biotin或 boronic acid 的修飾後，能藉由這些具選擇性的表面受體來感測相對應的生物分子，並藉由反應前後的電訊號變化來觀察反應是否進行。這個電性變化是由分別帶有負電荷或正電荷的分子靠近N-type 的電晶體所造成的，因此可證明此電晶體具有感測能力。接著我們證明奈米線場效電晶體的元件靈敏度可藉由外加的liquid-gate 來調控，這使此奈米線場效電晶體可發揮出元件的感測極限值，並輕易的找出適當的外加電壓值。最後我們藉由conductance-time 量測方式來測試EV71 DNA oligonucleotides，測試結果顯示此奈米線場效電晶體能感測到1fM 範圍的極低濃度。由於此製程方式相當簡單、成本低廉且具有相當高的感測靈敏度，因此具有很大的潛力來發展成為未來的醫療用生物感測器。

A simple and low-cost method to fabricate poly-silicon nanowire field effect transistor (poly-Si NW FET) for biosensing application was demonstrated. The poly-silicon nanowire (ploy-Si NW) channel was fabricated by employing the poly-silicon (poly-Si) sidewall spacer technique, which approach was comparable with current commercial semiconductor process and forsaken expensive E-beam lithography tools. The electronic properties of the poly-Si NW FET in aqueous solution were found to be similar to those of single crystal silicon nanowire field effect transistors. Passivation of defects in the poly-SiNW by H+ or OH- contained in the aqueous solution is proposed to explain the phenomenon. First, two experiments of biotin-avidin/streptavidin and boronic acid-dopamine sensing with ID-VG measurement were used to demonstrate the biological and chemical species sensing capacity of poly-Si NW FET. Specific changes were observed for electric measurements made with nanowire surface modified with biotin or boronic acid for avidin/streptavidin and dopamine sensing. The changes of ID-VG curves were consistent with an n-type FET affected by a nearby negatively and positively charged molecules, respectively, and demonstrated sensitive and label-free senisng capacity. Then, we have demonstrated that the sensitivity of an NW biosensor can be electrically modulated through liquid gating. Our findings open a window toward understanding how liquid gating can be used to electrically modulate the sensitivities of biosensors to their limits. Final, we test the device with conductance-time detection of EV71 DNA oligonucleotides. The results indicate that less as 1fM EV71 DNA target to the EV71 DNA probe modified poly-Si NW FET may induce the observed conductance-time curve changes. This unique electronic property together with its high sensitivity, simplicity, low-cost manufacturing and potential for mass commercial production makes the poly-Si NW FET very attractive for applications as transducer of biosensing device.