Ratiometric fluorometric detection of urinary sarcosine via GSH@Hg/carbon dots/sarcosine oxidase sensing platform: A non-invasive approach for prostate cancer diagnosis.

Sarcosine (N-methylglycine) has emerged as a promising biomarker for prostate cancer detection and progression monitoring, with elevated urinary levels strongly correlating with malignancy development and metastatic potential. In this study, we report a novel ratiometric fluorometric sensing platform for selective and sensitive sarcosine quantification based on a multi-component GSH@Hg/CDs/sarcosine oxidase system. The detection mechanism ingeniously exploits the enzymatic conversion of sarcosine by sarcosine oxidase (Sox) to produce hydrogen peroxide, which subsequently mediates glutathione oxidation and releases mercuric ions from GSH complexes. The liberated Hg ions interact differentially with dual-emission carbon dots, simultaneously quenching blue fluorescence (λ = 390 nm) while enhancing red emission (λ = 600 nm). This bidirectional signal modulation enables robust ratiometric measurements, substantially improving analytical reliability compared to conventional single-output methods. The sensing system demonstrates excellent linearity across the clinically relevant concentration range of 0.1-6.0 μM (r = 0.9938) with a remarkably low detection limit (0.072 μM). The method exhibits minimal interference from potential urinary interferents, as evidenced by high recovery values (97.00-99.20 %) in spiked samples. We have successfully validated this analytical platform using clinical urine specimens from healthy individuals and prostate cancer patients at various disease stages, demonstrating its practical applicability for evaluating sarcosine concentrations in individuals with suspected prostate malignancies. Our findings highlight the potential of this sensing platform as a non-invasive diagnostic and disease monitoring tool with remarkable discriminatory capability and complementary value to traditional PSA testing.