Optical response of HRP-modified porous SiO
to enzymatic reaction products infiltrating into the nanostructure. The HRP-modified PSiO2 nanostructure is pretreated with 50-mM PBS (pH 7.4) to minimize nonspecific adsorption of proteins. (a) Wash with 0.8-mM 4-chloro-1-naphthol in PBS buffer (pH 7.4). (b) Addition of H2O2 to the cycled solution. The PSiO2 biosensor is fixed in a custom-made flowcell, and the reflectivity spectra are recorded every 30 s. Inset: oxidation of 4-chloro-1-naphthol in the presence of HRP and H2O2.