NO₂ Detection Using Microcantilever Based Potentiometry

A highly sensitive and novel sensor platform for gases and volatile chemicals using microcantilever based potentiometry is reported. A resonant cantilever is used to detect the changes in surface work functions of functionalized substrates caused by adsorption of target gas molecules. Surface work function (SWF) changes were measured for different functionalization layers made of transition metal oxide thin films with the flow of NO₂. The rate of change in SWF for In₂O₃ and SnO₂ were found to be ~80 and ~100 μV/sec, respectively, for 70 ppm NO₂. A sensitivity of 64 μV/sec for SWF change was also found for 70 ppm NO₂ concentration for isolated clusters of ZnO nanowires, indicating that this technique is applicable even for nano-clusters of sensing materials where amperometric detection is impossible due to material discontinuity. NO₂ detection as low as 400 ppb was possible using highly insulating In₂O₃ and SnO₂ thin films (resistivity > 1 TΩ/⎕). Two different forms of nano scale graphite were compared with the transition oxide based functionalization layer for sensing sub-ppm NO₂ sensing. It was observed that nanostructured graphite (NG) shows much higher sensitivity and lower response time than transition metal oxides.