Electrochemical assay for the determination of nitric oxide metabolites using copper(II) chlorophyllin modified screen printed electrodes

This work presents a novel electrochemical assay for the collective measurement of nitric oxide (NO) and its metabolites nitrite (NO2−) and nitrate (NO3−) in volume miniaturized sample at low cost using copper(II) chlorophyllin (CuCP) modified sensor electrode. Zinc oxide (ZnO) incorporated screen printed carbon electrode (SPCE) was used as a host matrix for the immobilization of CuCP. The morphological changes of the ZnO and CuCP modified electrodes were investigated using scanning electron microscopy. The electrochemical characterization of CuCP–ZnO–SPCE exhibited the characteristic quasi-reversible redox peaks at the potential +0.06 V versus Ag/AgCl. This biosensor electrode showed a wide linear range of response over NO concentrations from 200 nM to 500 μM with a detection limit of 100 nM and sensitivity of 85.4 nA μM−1. Furthermore, NO2− measurement showed linearity of 100 nM to 1 mM with a detection limit of 100 nM for NO2− and sensitivity of 96.4 nA μM−1. Then, the concentration of NO3− was measured after its enzymatic conversion into NO2−. Using this assay, the concentrations of NO, NO2−, and NO3− present in human plasma samples before and after beetroot supplement were estimated using suitable membrane coated CuCP–ZnO–SPCE and validated with the standard Griess method.