Sensitive detection and prostate cancer cellular evaluation of sarcosine via a fluorescence turn-on assay using an N-CQDs/Ag⁺ nanosensor

Sarcosine, a key oncometabolite in prostate cancer (PCa), has emerged as a promising biomarker for disease diagnosis and progression monitoring. However, conventional detection methods often rely on urine samples and are susceptible to interference from individual metabolic variations. In this study, we developed a novel "turn-on" fluorescence sensor based on nitrogen-doped carbon quantum dots (N-CQDs) and silver ions (Ag⁺) for the sensitive and selective detection of sarcosine. The sensing mechanism relies on the initial quenching of N-CQD fluorescence by Ag⁺, followed by enzymatic generation of H₂O₂ from sarcosine oxidation catalyzed by sarcosine oxidase (SOx). The produced H₂O₂ reduces Ag⁺ to Ag nanoparticles, thereby restoring the fluorescence of N-CQDs. The sensor demonstrated a linear response to sarcosine in the range of 10-60 µM with a detection limit of 2.1 µM, and exhibited high selectivity against common interfering substances. Furthermore, the platform was successfully applied to detect sarcosine in lysates of prostate cell lines, revealing significantly elevated sarcosine levels in androgen-independent PC-3 cells compared to benign (BPH-1) and androgen-sensitive (LNCaP) cells. This work presents a cost-effective, and cell-compatible fluorescence strategy for sarcosine detection, holding potential for PCa early screening and metabolic profiling.