Biomolecular recognition with a sensitivity-enhanced nanowire transistor biosensor.

In applications of silicon nanowire field-effect transistors (SiNW-FETs) as biosensors, the SiNW-FETs conventionally are all area modified (AAM), with receptors covering not only the minute SiNW surface area but also the relatively large surrounding substrate area. In this study, using a bottom-up technique, we successfully fabricated selective surface modified (SSM) SiNW-FETs with the receptors on the SiNW sensing surface only. In this approach, the strategy was to modify the SiNWs with a chemical linker of 3-aminopropyltrimethoxysilane (APTMS) prior to photolithographic fabrication of the device. The APTMS molecules modifying the SiNWs survived the harsh photolithographic processes, including coating with photoresist, washing with organic solvent, and thermal annealing. These SSM SiNW-FETs also exhibited desirable electrical characteristics such as ohmic contact and high transconductance. Using the biotin-avidin binding system, we showed that the faster response time and smaller sample requirements of the SSM SiNW-FETs, relative to the conventional AAM SiNW-FETs, clearly show that restricting the surface modification of the SiNW-FETs substantially improves their detection sensitivity. Detection with a SSM boronic acid-modified SiNW-FET of the dopamine released under high-K(+) buffer stimulation from living PC12 cells also demonstrates that SiNW-FETs can serve as highly sensitive biosensors for biomedical diagnosis. In binding affinity measurements with SiNW-FETs, the dissociation constants (Kd) of the biotin-avidin and dopamine-boronic acid complexes were determined to be 15 ± 1 fM and 33 ± 8 fM, respectively.