Zinc oxide (ZnO) is considered to be one of the most promising candidates for the third-generation DNA biosensor because of its good chemical stability, wonderful biocompatibility, easy surface modification, and numerous kinds of nanostructures. In this work, we report a new and simple method to modify ZnO surface for the immobilization of oligonucleotides by electrochemical covalent grafting of diazonium salts. The atomic force microscope, X-ray photoelectron spectroscopy, surface contact angle system, and electrochemical workstation were employed to characterize the functionalization process. Fluorescence results show that this kind of DNA biosensor from covalently linking strategy has an enhanced performance compared to that based on an electrostatic adsorption route. The functionalized ZnO biosensor has the capability to distinguish four-base mismatched, one-base mismatched, and complementary DNA sequences. Moreover, a linear relationship has been observed between the fluorescence intensity and the concentration of the complementary DNA in the solution within the range from 10(-6) to 10(-9) M, offering us a possibility in the qualitative determination of the level of target DNA.
Keywords: DNA biosensor; ZnO; covalent bond; electrochemistry; fluorescence; functionalization.