矽奈米線場效應電晶體在細菌線毛上的偵測

Abstract

隨著奈米元件之蓬勃發展，奈米線/奈米管場效應電晶體對生物領域的研究，漸漸觸及各類系統，小至DNA 大至神經細胞活動的偵測。因為元件尺度的縮減，使得電子或電洞被侷限於較小的空間活動，除了載子之移動速率增加外，元件表面的電位(potential)變化對元件內之電流影響也比傳統之MOSFET大，靈敏度的增加很顯著，在沒有外力驅動待測物的條件下，光靠擴散，偵測力可達10-12 M。 線毛 (pili)，在細菌的接合生殖(conjugative gene transfer)與平行基因移轉(horizontal gene transfer)中扮演了極為重要的角色。線毛類似生物的奈米管，由一顆一顆的蛋白質所組裝成，直徑約為十奈米，長度可達數微米，內部有兩奈米的空腔。傳統上只能大量表現後，以穿遂式電子顯微鏡或電泳等方式來證明它的存在。對於細菌間的接合生殖，一直以來存在著兩種說法，一種是線毛扮演著繩索的角色，拉近兩隻細菌，而後細胞壁穿孔，質體(plasmid)由孔洞中經過；另一種說法，線毛扮演著輸送管的角色，兩隻細菌不必有直接的細胞壁接觸，光靠線毛內部的空腔，就足以輸送質體到另一隻細菌上。而對於後者的猜測，目前都只有間接證據。 本研究之最終目的將以矽奈米線場效應電晶體來研究細菌間的接合生殖之相關主題，但在這長程計劃的第一步，我們得先了解線毛與矽奈米線場效應電晶體之結合及其相應的訊號。在此篇論文，我們以農桿菌(Agrobacterium tumefaciens)的T-pili (T 線毛)為研究主體，在矽奈米線上修飾T-線毛抗體，有別於傳統，本研究以電學的方式，利用矽奈米線場效應電晶體的高靈敏度，測到了低於文獻一百萬倍(106)以上的濃度(10-12 M)，為下一步細菌接合生殖的研究，揭開了一個新的序幕。

Tremendous progress has been made in the development of nanowire/nanotube field effect transistors (FET) as biosensors in a variety of studies ranging from DNA, proteins, to neuronal signal propagation. With the reduction of device dimensions, the charge carriers are confined to move in a finite space, thus enhancing the carrier mobility that exceeds the limits of conventional MOSFET. Moreover, the carrier density can be altered by a small change of surface potential, resulting in the high sensitivity of NW/NT FET to a picomolarity level. Since the discovery of horizontal gene transfer in Agrobacterium tumefaciens in 1981, various investigations have been conducted to elaborate the mechanism of gene transfer. Although pilus which processes a 2 nm lumen in the center was found indispensable in the transfer process, there remain two debates. One argues that pili alone could transfer plasmids and served as conduit. The other states that cell contact is necessary for the plasmid transfer. Here, we apply silicon nanowire field-effect transistors (SiNW-FET), for the first time, as a sensitive tool to detect the T-pili in vitro with a very high sensitivity to a picomolarity level, thus offering a new opportunity to investigate the mechanism of gene transfer.