Ratiometric fluorescent detection system based on dual-driving catalysis of CuO nanozyme with a classical univariate calibration for the determination of ascorbic acid in serum and fruits

Copper oxide nanoparticles (CuO NPs) as nanozymes have received extensive attention due to their numerous advantages such as water solubility and biomimetic effects. In this work, we combined the inherent oxidase and ascorbate oxidase mimetic activity of CuO NPs to construct a ratiometric fluorescence system for the detection of ascorbic acid (Vitamin C, AA) in serum and fruits. By feat of the dual mimic nanozymatic activity of CuO NPs, the sole substrate o-phenylenediamine (OPD) can be catalyzed to attain yellow fluorescent 2,3-diaminophenazine (oxOPD), while oxidized AA will react with the pristine OPD to form blue fluorescent product. This method has a sensitive response to AA with a good linear relationship in the concentration range of 1–150 μM and low detection limit of 0.16 μM. Practical sample detection of AA in human serum and fruits can be realized reasonably with the recovery rates between 84.83% and 87.28% and 88.53%-113.1%, respectively. More conveniently, the method can be successfully used for scanning measurement analysis through the associated application (ColorAssist) on smartphones and portable UV lamps.