Quasi-reversible and direct electrochemistry has been observed at a new electrochemical interface constructed by functionalization of porous silicon microcavities (PSiMc) with either amino (APTES) or mercapto (MPTS) propyltriethoxysilane and the redox protein cytochrome c (cyt c). The high specific surface area, tunable pore size (observed by scanning electron microscopy) and functional surface of PSiMc permitted the infiltration of molecular binders and cyt c into the porous structure. The optical response of PSiMc was evaluated during all modification steps. In all the cases a red shift in the reflectance spectra after substrate modification was observed, indicating the infiltration and immobilization of organic binders and the cyt c protein. Dose-response curves demonstrated that biofunctionalization with APTES followed by glutaraldehyde (GTA) amine activation provides higher amounts of immobilized protein with 4.73 nmol protein/cm(2) of etching area compared with 1 nmol protein/cm(2) when using MPTS as a molecular binder. Infrared spectroscopy (FTIR) also demonstrated the adsorption of the protein within the surface nanostructure. The PSiMc/cyt c hybrid devices showed high electrochemical stability due to the retaining of the protein's redox activity even after several months of its immobilization (C) 2014 Elsevier Ltd. All rights reserved.