Sensitivity enhancement of a QCM biosensor using polymer treatment

Quartz crystal microbalances (QCMs) have been widely used for detection of various chemical and biological species in liquid media. We report an improved binding of protein A and IgG molecules on QCM biosensors by modifying the gold surface of the quartz crystal with a 35 nm polystyrene film followed by an acidic treatment. An appreciable increase in the frequency shift was observed when the polystyrene film was used as an interfacial layer. Protein A and IgG immobilizations on quartz crystals with the polystyrene film represented a 65% increase and a 40% increase respectively when compared to immobilization done directly onto the crystals. Complementary atomic force microscopy (AFM) studies revealed a significant decrease in the RMS roughness of the substrate from 98.4 nm to 1.75 nm when coated with polystyrene. This increased surface smoothness resulted in higher biomolecular coverage on the surface of the sensor causing higher frequency shifts.