The effects of hydrogen peroxide on the electrochemical decomposition of layer-by-layer thin films composed of 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) and avidin were studied. An ib-PEI/avidin thin film prepared on the surface of a platinum (Pt) film-coated quartz resonator was electrochemically decomposed in the presence of hydrogen peroxide (H2O2) in the solution. The resonant frequency of the thinfilm-deposited quartz resonator was increased upon application of electric potential (0.4-0.6 V vs Ag/AgCl) to the Pt layer, suggesting that the mass on the quartz resonator was decreased as a result of decomposition of the ib-PEI/avidin film. It was found that decomposition of the film is highly accelerated in the presence of H2O2 Compared to the decomposition in the same buffer solution without H2O2, due to a pH change originating from electrochemical oxidation of H2O2 on the Pt surface. The rate of electrochemical decomposition of the ib-PEI/avidin film was highly dependent on the concentration of H2O2, buffer capacity, and pH of the solution. (C) 2007 Elsevier Inc. All rights reserved.