Effect of silver nanoparticles on the electron transfer reactivity and the catalytic activity of myoglobin

Silver nanoparticles (11 ± 1.5 nm) could greatly enhance the electron-transfer reactivity of myoglobin (Mb) and its catalytic ability toward hydrogen peroxide (H₂O₂). Direct fast electron transfer between Mb and a pyrolytic graphite (PG) electrode was achieved, and a pair of well-defined, quasireversible redox peaks was obtained. The cathodic and anodic peaks were located at -329 and -281 mV, respectively. Meanwhile, the catalytic ability of the protein toward the reduction of H₂O₂ was also studied, and a H₂O₂ biosensor was subsequently fabricated. Its detection limit was 1.0 × 10^-6M with a sensitivity of 0.0205 μA per μM of H₂O₂. The apparent Michaelis-Menten constant was calculated to be 1303 μM. Flocculation assay showed that the protein maintained plasmon layers surrounding the surface of silver nanoparticles and avoided silver-nanopartkle aggregation. On the other hand, UV-visible spectroscopy studies revealed that silver nanoparticles could induce a small change of the heme-group environment of the protein; this contributed to the enhancement of the electron-transfer reactivity and the catalytic activity.