Abstract
Quartz crystal microbalances (QCM) loaded with poly(N-isopropylacrylamide; NIPA) or poly(N-isopropylacrylamide-acrylic acid, sodium salt; NIPA-SA) micro-hydrogels were prepared. Oscillation frequency of the QCMs for the series of solutions was measured as a function of solution temperature and concentration of additive adsorbates (acrylic acid; AAc and Cu2+ ion) in the solutions. The QCM loaded with the gels showed the characteristic oscillation behavior responding to the phase behavior of gels. Drastic shift of the oscillation frequency was observed at the phase transition temperature, TP, of the gels. The critical temperature TP at which the drastic change in the oscillation frequency shift appeared decreased by the addition of adsorbates. The change in hydrophobic/hydrophilic balance of the gels due to the adsorption of additives onto the gel resulted in the shift of the critical temperature. The results obtained in this study demonstrated that stimuli-sensitive polymer hydrogel coupled with QCM is a promising device for molecular sensing through the adsorption induced phase change of the gel.
