Sensitivity enhancement in photoionization detector using microelectrodes with integrated 1D nanostructures

Photoionization detectors (PIDs) that use high-energy photons to ionize gas molecules have attracted considerable attention as volatile organic compound (VOC) sensors owing to their high sensitivity, selectivity, and reliability. Recently, miniaturized PIDs have been developed to further improve the sensing performance. However, most studies have focused solely on the miniaturization of the ionization chamber, although the electrode is an important factor for determining the sensitivity and operation voltage. This work demonstrates a PID composed of Si microelectrodes fabricated via microfabrication with one-dimensional (1D) nanostructures coated on them. The interdigitated microelectrodes offer a larger surface area capable of enhanced capturing of positively charged ions and electrons compared to typical mm-scale electrodes, resulting in the successful detection of 500 ppb toluene at an applied voltage of 0.2 V. Furthermore, taking advantage of the outstanding surface-to-volume ratio of 1D nanostructures, Ag nanowire-coated microelectrodes and carbon nanotube (CNT)-coated microelectrodes exhibit 38% and 76% improvement in sensitivity, respectively, than the bare Si microelectrodes. The CNT-coated microelectrodes show superior linearity and repeatability at toluene concentrations from 0.1 to 1.0 ppm. The proposed PID will be a promising candidate for portable VOC sensors.