Zinc oxide nanowires on customized nanogap chip for high resolution protein nano sensor.

We demonstrate a nano Field Effect Transistor (FET) biosensor using zinc oxide (ZnO) nanowire aligned on gold nanogap electrodes. Nano-FET biosensors are an emerging nanoelectronic technology capable of real-time and label-free quantification of soluble biological molecules. The device consists of a single functionalized ZnO nanowire, as the conducting channel to detect proteins, and of aligned gate electrodes with well-defined nanosized gaps. ZnO were synthesized by hydrothermal reaction and chemically functionalized with amino-propyl groups. We positioned single wires through dielectrophoresis across nanogap electrodes, using a custom platform based on a chip constituted by four nanogaps, thus leading to the parallel positioning and testing of four ZnO wires. Nanogap electrodes with a controlled nanometric separation were ad-hoc fabricated by Electromigration-Induced Break Junction (EIBJ) using a low-cost electronic system. The obtained FETs have a n-type channel and operate in enhancement mode. We have proved the binding of bovine serum albumin (BSA) to demonstrate the effectiveness of the device architecture. The binding was conducted with EDC-amidation reaction among the amine groups of the functionalized ZnO and the carboxyl groups of the protein. The whole process serves as a model system to study in-situ and as a function of time the protein interaction with the ZnO surface.. By dropping a tiny amount of BSA solution with the specific reagents for the EDC-amidation reaction on the ZnO-nanogap chip, we were able to monitor the drain-source current IDS as a function of time. The results showed a constant reduction of the IDS upon protein binding to the ZnO surface, leading to a precise understanding of the protein-surface phenomena. We have also examined the dependence of the IDS as function of the gate voltage VG and we refer to this response as the “device characteristics”. To this end, we devised a novel nano-fabrication method for manufacturing an integrated, high-throughput, multiplexed real-time nano-FET biosensor.