Silicon resonant nanopillar sensors for airborne titanium dioxide engineered nanoparticle mass detection

This work demonstrates mass measurement of airborne titanium dioxide (TiO2) engineered nanoparticles (ENPs) using silicon resonant nanopillar sensors by monitoring resonant frequency shifts induced by the mass of trapped ENPs. Inductively coupled plasma (ICP) cryogenic dry etching and thermal oxidation have been used in the sensor fabrication. A piezo shear actuator and an electrostatic precipitator are utilized to excite the nanopillars in resonant mode and collect the flowing TiO2 ENPs, respectively. By using the fundamental bending frequency, the sensor can achieve a mass sensitivity of 7.22 Hz/fg, which enables its application to a nanobalance to detect airborne ENPs in the femtogram mass range. Two methods of ENP removals (i.e., polydimethylsiloxane (PDMS) and ultrasonic cleanings) have also been performed to remove the adhered ENPs, thus efficiently extending the operating life of the sensor. This developed sensor is targeted to be implemented as a handheld ENP monitoring device at workplaces.