A hydrogen peroxide biosensor based on the direct electrochemistry of hemoglobin modified with quantum dots

Direct electron transfer of hemoglobin modified with quantum dots (QDs) (CdS) has been performed at a normal graphite electrode. The response current is linearly dependent on the scan rate, indicating the direct electrochemistry of hemoglobin in that case is a surface-controlled electrode process. UV-vis spectra suggest that the conformation of hemoglobin modified with CdS is little different from that of hemoglobin alone, and the conformation changes reversibly in the pH range 3.0-10.0. The hemoglobin in a QD film can retain its bioactivity and the modified electrode can work as a hydrogen peroxide biosensor because of its peroxidase-like activity. This biosensor shows an excellent response to the reduction of H2O2 without the aid of an electron mediator. The catalytic current shows a linear dependence on the concentration of H2O2 in the range 5 x 10(-7) -3 x 10(-4) M with a detection limit of 6 x 10(-8) M. The response shows Michaelis-Menten behavior at higher H2O2 concentrations and the apparent Michaelis-Menten constant is estimated to be 112 mu M.