Quartz crystal microbalance (QCM) sensor for CH3SH gas by using polyelectrolyte-coated sol–gel film

A new structure of sensing film for QCM sensor electrode was investigated. Gas-sensing device for toxic gases requires high sensor sensitivity and quick response. Increasing the surface area of sensing film was effective to improve the sensor sensitivity and response speed of QCM sensors, however it is difficult to increase the surface area of polymeric film. In this paper, Al2O3 porous film was coated on QCM substrate by sol–gel method between the QCM electrode and polymeric layer in order to increase the surface area of polymeric layer. By using this manner, polymeric sensing films with high porosity can be fabricated without high-temperature treatment. The sensor was evaluated for the detection of methyl mercaptan (CH3SH) by using poly(ethylene imine) (PEI) as polymeric layer. The sensor with Al2O3 porous layer showed high sensitivity and quick response rather than the sensor without the inorganic layer. The Al2O3 layer worked for increasing the surface area of polyelectrolyte layer which resulted in the increasing of the sensor sensitivity.