Bioactivity of horseradish peroxidase entrapped in silica nanospheres

Interest in the fabrication of micro/nanoreactors for evaluation of the function of biomolecules in biological processes, enzymatic reaction kinetics occurring inside the nanospace is rapidly increasing. With a simple reverse-micelle microemulsion method, horseradish peroxidase (HRP), a model biomolecule, was herein skillfully confined in silica nanoshells (HRP@SiO(2)) and its biocatalytical behaviors were investigated in detail. Spectroscopic measurements showed that the entrapped HRP molecules retained their native structure and had high enzymatic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) with Michaelis constant (K(m)) of 3.02 × 10(-5) mol L(-1). The entrapped HRP displayed a good direct electron transfer behavior and sensitive electrocatalytic response toward the reduction of H(2)O(2), which could be enhanced using thionine and o-phenylenediamine (o-PD) as electron mediators. When using thionine as mediator, the mass transport between the substrates in electrolyte and HRP confined in silica nanospheres through the mesoporous tunnels was slower than that of o-PD, which slowed down the electron transfer between heme in HRP in the confined nanospace and the electrode, and resulted in low sensitivity to H(2)O(2) with thionine as mediator when compared to o-PD.