Switch-on fluorescent strategy based on N and S co-doped graphene quantum dots (N-S/GQDs) for monitoring pyrophosphate ions in synovial fluid of arthritis patients

This work reports a facile and effective approach for preparing graphene quantum dots co-doped with nitrogen and sulfur (N-S/GQDs). The proposed method comprised pyrolysis of citric acid with glutathione and dialysis treatment. The fabricated N-S/GQDs exhibited blue luminescence and a high fluorescence quantum yield of 36.3%. N-S/GQDs can be sensitively quenched by Fe3+, which was absorbed on the edge of N-S/GQDs through the coordination interaction between Fe3+ and N, S elements. The subsequent introduction of pyrophosphate ion (PPi) resulted in the recovery of the fluorescence of Fe3+-quenched N-S/GQDs. The stronger coordination reactivity between Fe3+ and PPi induced changes in fluorescence. PPi concentration was facilely quantified through the recovered amplitudes of the fluorescence intensities of N-S/GQDs. Under the optimized experimental condition, increased fluorescence intensity showed a linear relationship to PPi concentration (1 μM to 1000 μM) in serum samples. Additionally, the proposed method featured sensitive and selectivity for the detection of PPi in synovial fluid, suggesting the potential application for simple and accurate clinical diagnosis of arthritic diseases.