ZnO nanoparticle/nanorod-based label-free electrochemical immunoassay for rapid detection of MMP-9 biomarker

A label-free electrochemical biosensor was developed for the rapid detection of the matrix metalloproteinase 9 (MMP-9) biomarker on the basis of antibody immobilizing on the zinc oxide (ZnO) nanoparticle and ZnO nanorod electrodes. The charge transfer resistance (R-ct) of the electrodes was used as the indicator for MMP-9 concentration, which was obtained through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The ZnO nanorod-based biosensor exhibited linear behavior in the MMP-9 concentration range of 1-1000 ng/ml, which is a wider range than the available concentration ranges for most of the conventional methods. The biosensor sensitivity was 32.5 mu A/(decade x cm(2)) with a detection time of only 35 min. Moreover, the results from the developed biosensor were comparable with those measured with a commercial enzyme-linked immunosorbent assay (ELISA) for real samples showing less than 8% difference. The presented MMP-9 biosensor is potentially applicable to the analysis of biological samples, especially in point-of-care (POC) diagnosis or urgent cases analysis, considering its simple fabrication, similar accuracy, shorter detection time, and ease of usage compared with traditional methods such as ELISA.