Electrochemical biosensor for the detection of H₂O₂ from living cancer cells based on ZnO nanosheets

In this work, direct electron transfer of cytochrome c (cyt. c)-a model for studying the electron transfer of enzymes is achieved at hexagonal ZnO nanosheets by one-step electrodeposition. UV-vis spectra and electrochemical data demonstrate that such ZnO nanosheets can supply a bio-compatible surface to keep the bioactivity of cyt. c. The redox formal potential (E⁰') of cyt. c is estimated to be 338.2±4.3mV (vs. Ag|AgCl) at the nanostructured ZnO surface. This value is much more positive than those of enzymes previously obtained at other metal oxides and zeolite surfaces. Experiment data show, under the optimized potential of 0.0V (vs. Ag|AgCl), the electrochemical determination of H₂O₂ is free from not only anodic interferences like ascorbic acid (AA) and dopamine (DA), but also a cathodic interference-O₂. Such an excellent selectivity enable the present H₂O₂ biosensor determine the extracellular H₂O₂ released from living human hepatoma cells.