Antibody/antigen affinity behavior in liquid environment with electrical impedance analysis of quartz crystal microbalances

Electrical impedance analysis has been used to study anti-human immunoglobulin G (anti-h IgG) adsorption and the subsequent human immunoglobulin G (hIgG) or rabbit immunoglobulin G (rIgG) affinity reaction in aqueous liquids on a polystyrene (PS)-modified quartz crystal microbalance (QCM) surface. Time-dependent adsorption data of both the frequency shift and the electrical equivalent parameters (motional resistance, shunt capacitance, quality factor, etc) are monitored. It was found that the motional resistance, R, increases while the resonance frequency, f, decreases during both the anti-h IgG immobilization and the subsequent affinity process. Decreasing f primarily arises from the increased mass loading. Increasing R indicates more power dissipation (increased losses) in the system. The change in motional resistance, ΔR, in the affinity reaction is considerably larger than that in anti-h IgG immobilization adsorption process, although the resonant frequency shifts, Δf, are very close in these two processes. Specifically, for a saturated solution, the ratio of ΔR/Δf is 9.45×10^-3 Ω/Hz for anti-h IgG adsorption and 28.1×10^-3 Ω/Hz for anti-h IgG/hIgG binding respectively, indicating the increased power dissipation with the increasing binding molecules. The shunt capacitance changes little in the hIgG binding process (∼0.01 pF).