Self-regenerating photocatalytic sensor based on dielectrophoretically assembled TiO2 nanowires for chemical vapor sensing

In this paper we reported a new method to fabricate TiO2 based chemical vapor sensor fabricated by dielectrophoretically assembling TiO2 nanowires. Although TiO2 based chemical sensors were previously reported, they were usually fabricated by the bottom-up methods, which involve tedious processes and cannot be scaled-up. In the current paper, we presented a top-down approach in the fabrication of TiO2 nanowire based sensors. The TiO2 nanowires were initially synthesized and subsequently directly assembled between two co-planar electrodes by dielectrophoresis in microfluidic devices. We used two different methods, ethylene glycol-mediated hydrolysis and high-voltage electrospinning, to synthesize TiO2 nanowires with varied diameters and lengths. By incorporating a laminar flow field with AC electric fields, the control of the density of assembled TiO2 nanowires was achieved adjusting AC frequencies and flow rates, which rendered this method repeatable and scalable for the fabrication of TiO2 nanowire based devices. The sensing performances of chemical sensors based on the two kinds of TiO2 nanowires were tested and compared. In the sensing experiments UV light was applied to activate the surface of TiO2 nanowires, allowing them to be operated at room temperature. The results showed that the sensitivity of the self-regenerating chemical sensor based on TiO2 nanowires synthesized by electrospinning exhibited 4.37 times higher than that of the nanowires prepared by the glycol-mediated hydrolysis method. The chemical sensor based on electrospun TiO2 nanowires showed high sensitivity, fast response (less than 60 s) and fast recovery (less than 60 s) to vapor pollutants including NH3, acetone, and ethanol.