MXene Nanosheet-Derived N, S-Codoped Quantum Dots for Ultrasensitive Detection of 3-Nitro-L-Tyrosine in Biological Fluids

3-Nitro-L-tyrosine (3NT) is an oxidative stress metabolite of neurodegenerative diseases, and the rapid and effective detection of 3NT in human fluids for early diagnosis is important. Herein, for the first time, the nitrogen, sulfur co-doped graphene quantum dots derived from nitrogen-doped Ti3C2Tx MXene nanosheet via the hydrothermal method in the presence of mercaptosuccinic acid was synthesized as an optical sensing probe to detect 3NT in human serum. Tetramethyl ammonium hydroxide, the nitrogen source and delamination agent, was used to prepare nitrogen-doped MXene nanosheets via one step at room temperature. The as-prepared NS-MXene QDs (NSMQDs) are uniform with an average size of 1.2 ± 0.6 nm, and can be stable in aqueous solution for at least 90 d to serve as the fluorescence probe. The N atoms in N-MXene reduce the restacking and aggregation of MXene nanosheets, while the sulfur dopant in NSMQDs increases the quantum yield from 6.2 to 12.1% as well as enhances the selectivity of 3NT over the other 12 interferences via coordination interaction with nitro group in 3NT. A linear range of 0.02 – 150 µM in PBS and 0.05 – 200 µM in human serum with a recovery of 97 – 108% for 3NT detection is observed. Moreover, the limit of detection can be lowered to 4.2 and 7 nM in PBS and 1× diluted human serum, respectively. Results obtained clearly indicate the potential application of the N-Ti3C2Tx derived NSMQD for effective detection of 3NT, which can open a window for the synthesis of doped MQDs via 2D MXene materials for ultrasensitive and selective detection of other biometabolites and biomarkers of neurodegenerative diseases in biological fluids.