The affinity of the polydopamine-induced-PEG to the surface was studied by quartz crystal microbalance (QCM; Seiko QCM 922, Princeton Applied Research Inc., Oak Ridge, TN, USA). Mass variation before and after coating was measured. The change of the effective surface mass on the quartz crystal altered the gold resonant frequency. The differences in the resonant frequency were recorded as a function of the potential, and the corresponding mass changes were calculated. The experimentally determined Sauerbrey constant for the gold resonator was 176.0 Hz cm2·µg−1 .