Horseradish peroxidase-modified porous silicon for phenol monitoring

• Horseradish peroxidase enzyme (HRP) was covalently immobilized on porous silicon (PSi) surface.
• Multistep strategy was used allowing the maintaining of the enzymatic activity of the immobilized enzyme.
• Direct electron transfer has occurred between the immobilized enzyme and the surface.
• Electrochemical measurements showed a response of HRP-modified PSi toward phenol in the presence of H2O2.

In this study, horseradish peroxidase enzyme (HRP) was covalently immobilized on porous silicon (PSi) surface using multistep strategy. First, acid terminations were generated on hydrogenated PSi surface by thermal hydrosilylation of undecylenic acid. Then, the carboxyl-terminated monolayer was transformed to active ester (succinimidyl ester) using N-hydroxysuccinimide (NHS) in the presence of the coupling agent N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide (EDC). Subsequently, the enzyme was anchored on the surface via an amidation reaction. The structure of the PSi layers was observed by scanning electron microscopy (SEM). Infrared spectroscopy (FTIR) and contact angle measurements confirmed the efficiency of the modification at each step of the functionalization. Cyclic voltammetry was recorded using the HRP-modified PSi as working electrode. The results show that the enzymatic activity of the immobilized HRP is preserved and in the presence of hydrogen peroxide, the enzyme oxidizes phenolic molecules which were subsequently reduced at the modified-PSi electrode.

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