Electrical properties of core-shell nanoparticles with protein shell layers have not been fully surveyed, although such nanoparticles have been studied widely as model biomimetic particles. In this study, we demonstrated that the capacitance changes of a silica (SiO2)/bovine serum albumin (BSA) core-shell nanoparticle (SiO2@BSA) could be monitored with variation of BSA shell thickness using AC impedance spectroscopy combined with conductive atomic force microscopy (c-AFM). Impedance spectra showed that the resistance and capacitance of SiO2@BSA core-shell nanoparticles increased with increasing BSA shell thickness. Within the range of experimental conditions studied, the capacitance of SiO2@BSA increased linearly with increasing number of BSA layers, corresponding to a 5.4 pF rise per single layer of BSA after the first two layer deposition of BSA. This result demonstrated that the minute changes of the electrical properties that were induced by the shell protein layer can be monitored and quantified using impedance spectroscopy. (C) 2015 The Electrochemical Society. All rights reserved.