Bio-functionalization of ZnO water gated thin-film transistors

ZnO based thin-film transistors are very promising to be used as electronic biosensors due to their very good electronic performances and inherent biocompatibility. Herein, we report on the use of a solution processed ZnO water gated thin-film transistor (WG-TFT) whose channel surface is bio-functionalized with a streptavidin protein layer. This is a very critical process as it endows the device with bio-recognition capabilities. The bio-functionalization process is carried out by attaching an organosilane self-assembled monolayer to the ZnO surface that is coupled to the biomolecule afterwards. A systematic X-Ray Photoelectron Spectroscopy surface characterization allows assessing that the immobilization of the streptavidin proteins on the ZnO surface has been successfully accomplished. Upon deposition of the protein layer, a decrease in the ZnO WG-TFT source-drain current is observed. Such an occurrence is ascribable to the electrostatic effect of the negatively charged protein molecules lying on the ZnO semiconductor layer in contact with the transistor 2D-channel. The deposited streptavidin layer can be prospectively further used for the immobilization and orientation of biotinylated recognition elements in view of the use of ZnO TFTs as electronic biosensors for real-life applications.