Oppositely charged poly(allylamine hydrochloride) (PAH) and 5 nm-sized TiO2 nanoparticles were assembled into {PAH/TiO2}(n) layer-by-layer (LBL) films on electrodes. The cyclic voltammetric (CV) response of K3Fe(CN)(6) at {PAH/TiO2}(n) film electrodes was very sensitive to the solution pH. At pH 4.0, the probe showed a nearly reversible CV peak pair with large peak currents; at pH 9.0, however, the CV response was significantly suppressed. This reversible pH-dependent on-off property could be used to switch the bioelectrocatalysis of H2O2 by horseradish peroxidase (HRP) with Fe(CN)(6)(3-) as the mediator by changing the surrounding pH. The mechanism of the pH-dependent permeability of the films toward the probe was explored and discussed by comparative experiments. (C) 2011 Elsevier B.V. All rights reserved.