Sensitive fluorescent detection of H2O2 and glucose in human serum based on inner filter effect of squaric acid-iron(III) on the fluorescence of upconversion nanoparticle

Diabetes mellitus is an epidemic disease that it has became a worldwide public health problem. Thus, blood glucose monitoring has attracted extensive attention. Here, we report a nanosensor based on inner filter effect (IFE) between upconversion nanoparticles (UCNPs) and squaric acid (SQA)-iron(III) for the highly sensitive and selective detection of glucose levels in human serum. In this assay, GOx-catalyzed oxidization of glucose produces gluconic acid and hydrogen peroxide (H 2 O 2 ). The latter can catalytically oxidize iron(II) to iron(III) which can rapidly (<1   min) coordinate with the SQA to produce (SQA)-iron(III). The absorption band of (SQA)-iron(III) largely covered the emission band of UCNPs, resulting the fluorescence emission of UCNPs was effectively quenched. Therefore, the glucose can be monitored based on the formation of SQA-iron(III). Under the optimal condition, the fluorescence quenching efficiency shows a good linear response to glucose concentration in the ranges of 7–340   μmol/L with a detection limit of 2.3   μmol/L. The developed method has been further applied to monitor glucose levels in human serum with satisfactory results. Compared with other fluorescence methods , current method displayed high sensitivity and signal-to-noise ratio. Meanwhile, this nanosystem is also generalizable and can be easily expanded to the detection of various H 2 O 2 -involved analytes.