Electrocatalysis via direct electrochemistry of myoglobin immobilized on colloidal gold nanoparticles

The direct electron transfer between immobilized myoglobin (Mb) and colloidal gold modified carbon paste electrode was studied. The Mb immobilized on the colloidal gold nanoparticles displayed a pair of redox peaks in 0.1 M pH 7.0 PBS with a formal potential of -(0.108 +/- 0.002) V (vs. NHE). The response showed a surface -controlled electrode process with an electron transfer rate constant of (26.7 +/- 3.7) s(-1) at scan rates from 10 to 100 mV s(-1) and a diffusioncontrolled process involving the diffusion of proton at scan rates more than 100 mV s(-1). The immobilized Mb maintained its activity and could electrocatalyze the reduction of both hydrogen peroxide and nitrite. Thus, the novel renewable reagentless sensors for hydrogen peroxide and nitrite were developed, respectively. The activity of Mb with respect to the pseudo peroxidase with a K (app)(M) value of 0.65 mM could respond linearly to hydrogen peroxide concentration from 4.6 to 28 muM. ne sensor exhibited a fast amperometric response to NO2- reduction and reached 93% of steady-state current within 5 s. The linear range for NO2- determination was from 8.0 to 112 muM with a detection limit of 0.7 M at 3a.