Peroxidase-Like Activity of Gold Nanoparticles and Their Gold Staining Enhanced ELISA Application

We found that the peroxidase-like activity of gold nanoparticles (GNPs) followed the Michaelis-Menten kinetic model and was dependent on environmental pH and temperature, which was very similar to natural Horseradish Peroxidase (HRP). However, unlike HRP, which needs a lower H₂O₂ concentration with a very narrow range to reach a maximum reaction rate and avoid enzyme poisoning, GNPs have very high activity, even at an H₂O₂ concentration two orders of magnitude higher than HRP. It was demonstrated that H₂O₂ treatment could enhance the peroxidase-like activity of GNPs, resulting thus in the activity increase in a circular catalytic reaction by the reduplicative use of GNPs. It was also found that the peroxidase-like activity of GNPs responded sensitively to nanoparticle size and surface modifications. When used in an immunoassay, GNPs were generally conjugated with antibody and blocked with hydrophilic macromolecules to construct a nanoprobe. This strongly reduced the peroxidase-like activity and detection sensitivity of GNPs, therefore, restricting their use as peroxidase mimetics. We presented a novel strategy that combined the nanoprobes with gold staining to expose fresh catalytic gold surfaces and obtained a great increase in detection sensitivity.