Nitrogen‐Doped Graphene Quantum Dot Fluorescent Nanosensor for Sensitive and Quantitative Detection of Tyrosine in Urine

To develop a sensitive and quantitative method for tyrosine detection in urine and evaluate its value in tumor screening. METHODS: ), with N-GQDs serving as the fluorescent nanosensor. The analytical performance was assessed in terms of linear range, limit of detection (LOD), selectivity, spike recovery, and precision. Receiver operating characteristic (ROC) analysis was performed to evaluate the screening performance in clinical samples. RESULTS: . For urinary tyrosine analysis, spike recoveries ranged from 87.4% to 106.6%, and the assay was not affected by common amino acids or inorganic ions present in urine. In clinical testing, urinary tyrosine levels measured by the N-GQDs-based fluorescent nanosensor were significantly higher in patients with malignant tumors, yielding an area under the ROC curve (AUC) of 0.832. CONCLUSION: A fluorescence nanosensor-based method using N-GQDs was developed for quantitative determination of urinary tyrosine, demonstrating promising value for tumor screening.