Polyelectrostatic immobilization of gold nanoparticles-modified peroxidase on alginate-coated gold electrode for mediatorless biosensor construction

Horseradish peroxidase was cross-linked with cysteamine-capped Au nanoparticles and further immobilized on sodium alginate-coated Au electrode through polyelectrostatic interactions. The electrode was employed for constructing a reagentless amperometric biosensor for H2O2. The electrode showed linear response (poised at −400 mV vs. Ag/AgCl) toward H2O2 concentration between 20 μM and 13.7 mM at pH 7.0. The biosensor reached 95% of steady-state current in about 15 s, and its sensitivity was 40.1 mA/M cm2. The detection limit of the enzyme-based electrode was determined as 3 μM, at a signal-to-noise ratio of three. The electrode retained 97% of its initial analytical response after 1 month of storage at 4 °C in 50 mM sodium phosphate buffer, pH 7.0. The stability of the biosensor was significantly reduced when it was incubated in high ionic strength solutions, retaining only 44% of its initial response after 1 month of storage at 4 °C in 1 M NaCl ionic strength in 50 mM sodium phosphate buffer, pH 7.0.