Electroactive Core−Shell Nanocluster Films of Heme Proteins, Polyelectrolytes, and Silica Nanoparticles

Abstract

Novel protein core−shell nanocluster films were assembled layer by layer on solid surfaces. In the first step, positively charged heme protein hemoglobin (Hb) or myoglobin (Mb) and negatively charged poly(styrenesulfonate) (PSS) were alternately adsorbed on the surface of SiO₂ nanoparticles, forming core−shell SiO₂−(protein/PSS)_m nanoclusters. In the second step, the SiO₂−(protein/PSS)_m nanoclusters and polycationic poly(ethylenimine) (PEI) were assembled layer by layer on various solid substrates, forming {[SiO₂−(protein/PSS)_m]/PEI}_n films. Various techniques were used to characterize the nanoclusters and monitor the film growth. {[SiO₂−(protein/PSS)_m]/PEI}_n films at pyrolytic graphite (PG) electrodes exhibited well-defined, chemically reversible cyclic voltammetric reduction−oxidation peaks characteristic of the heme Fe^III/Fe^II redox couples. The proteins in the films retained near native conformations in the medium pH range, and the films catalyzed electrochemical reduction of oxygen and hydrogen peroxide. Advantages of the nanocluster films over the simple {SiO₂/protein}_n layer-by-layer films include a larger fraction of electroactive protein and higher specific biocatalytic activity. Using this approach, biocatalytic activity can be tailored and controlled by varying the number of bilayers deposited on the nanoparticle cores and the number of nanocluster layers on electrodes.