Label-Free Simultaneous Analysis of Fe(III) and Ascorbic Acid Using Fluorescence Switching of Ultrathin Graphitic Carbon Nitride Nanosheets

A simple chemical oxidation and ultrasound exfoliation method has been developed to synthesize the two-dimensional and ultrathin-layer materials—graphitic carbon nitride nanosheets (g-C3N4 NNs). The prepared ultrathin g-C3N4 NNs display strong fluorescence and stability, including good photostability and excellent antisalt ability. Herein, a new “on–off–on” fluorescent switching sensor is designed. The iron ion (Fe3+) has an ultrasensitive response to quench the fluorescence of g-C3N4 NNs based on the synergistic effect between inner filter effect and photoinduced electron transfer. The linear limit for Fe3+ was from 0.05 to 30 μmol L–1 with a detection limit of 0.018 μmol L–1. Meanwhile, the fluorescence of g-C3N4 NNs can recover through the redox reaction between Fe3+ and ascorbic acid (AA). In addition, the linear range for AA was from 0.2 to 112.5 μmol L–1 with a 0.086 μmol L–1 detection limit. The proposed method exhibited rapid response, excellent selectivity, wide detection range, and low detection limit for simultaneous analysis of Fe3+ and AA, and it was applied for the determination of Fe3+ and AA in water sample and human serum with satisfactory results.