Surface Modification of Polystyrene Coating on QCM Sensor using Ambient Air Plasma at Low Pressure

Surface modification of quartz crystal microbalance Quartz Crystal Microbalance (QCM) sensor is crucial in the development of QCM sensor as a basis for biosensor and chemical sensor. Plasma technology has been used widely for surface modification such as cleaning, activation, deposition, etching, and ashing. In this work, we used ambient air plasma treatment to modify the hydrophobicity of polystyrene coating on the QCM sensor. The QCM sensor was coated with polystyrene using a spin coating and then heated at 200 °C. The plasma was generated in a low pressure (60 Pa) chamber filled with ambient air at a flow rate of 50 sccm. The power was supplied by a 2 MHz RF generator. The sensor was treated in air plasma chamber for 5 minutes. The result shows that variation in DC offset affects the hydrophobicity of the polystyrene surface. Under plasma exposure without DC bias, the polystyrene surface changes to hydrophilic significantly indicated by lower contact angle compare to the non-treated surface. There is no electrical impedance change of the QCM sensor with polystyrene coating before and after plasma treatment. It indicates that the acoustic impedance as a mechanical property of the polystyrene film on top of the QCM sensor remains.