Energy Dissipation Kinetics for Protein and Antibody−Antigen Adsorption under Shear Oscillation on a Quartz Crystal Microbalance

A new quartz crystal microbalance instrument, allowing simultaneous frequency (f) and dissipation factor (D) measurements, has been used to study protein adsorption kinetics by measuring time-resolved data of both the D-factor, measuring the energy dissipation due to the added overlayer, and the f-shift, measuring the effective mass load on the sensor. Four model proteins (myoglobin, hemoglobin, human serum albumin (HSA), ferritin) and one antibody−antigen reaction (antibody against HSA) were studied on a hydrophobic, methyl-terminated (−CH3) gold surface. In all five cases system-specific, positive D-shifts and negative f-shifts were observed, revealing different adsorption phases. The D-factor measurements provide new information about protein adsorption and improve the interpretation of the frequency shift in terms of mass uptake. Possible mechanisms for the adlayer-induced dissipation are discussed.