Nanogap field-effect transistor biosensors for electrical detection of avian influenza.

Field-effect transistor (FET)-type biosensors have shown potential for use in label-free electrical detection with high sensitivity. An ion-selective FET (ISFET) utilizes a reference electrode in the form of an aqueous solution. Its conductance is dependent on charged species on the surface of the ISFET. The sensitivity of nanowire FETs (NWFETs) is high enough to enable single-molecule detection due to the high surface-tovolume ratio of the nanowires, although the operational principle of NWFETs is similar to that of ISFETs. However, previous FET-type biosensors lack compatibility with the standard complementary metal oxide semiconductor (CMOS) process and monolithic integration with readout circuits and signal processing systems. In this Communication, we report the development of a nanogap FET fabricated by the standard CMOS process. After fabrication of a conventional FET with a top gate, which consists of a chromium layer and polycrystalline silicon on top of it, the chromium layer of the gate was selectively removed by wet-etching techniques to form a 20-nm-thick nanogap between the gate and the gate oxide on top of the channel. This approach enables researchers to realize on-chip integration of biosensors with readout circuits and signal processing