In this paper, methylene blue (MB)-doped silica nanoparticles (NPs) were prepared in a reverse microemulsion and used as a novel matrix for biochemical application. By controlling the experiment conditions, MB was successfully captured in a three-dimensional cage of the silica network. The silica matrix, with hydrophilic groups, provides a biocompatible microenvironment for heme proteins retaining their native conformation and biological activity. The chemical and electrochemical stability of NIB-doped silica NPs makes the organic-inorganic nanocomposite be a promising platform for bioelectrochemical analysis. Conjugated with chitosan, the NIB-doped silica NPs were modified on the surface of glassy carbon (GC) electrode. The developed electrode exhibited the remarkable catalytic activity for the reduction of hemoglobin (Hb) and cytochrome c (Cyt c). The catalytic reduction peak currents for chitosan/MB-doped silica NPs were linearly proportional to the concentrations of Hb and Cyt c. The calculated detection limits (S/N = 3) were 4.5 x 10(-9) mol/L for Hb and 5.0 x 10(-8) mol/L for Cyt c, respectively. (c) 2006 Elsevier Ltd. All rights reserved.