<p>A near-infrared (NIR) fluorescence sensing platform based on NIR carbon dots (CDs), gold nanoparticles (AuNPs) and sarcosine-specific aptamers (SA-Apt) was developed for the sensitive and selective detection of sarcosine (SA), a potential biomarker associated with prostate cancer. Nitrogen- and sulfur-co-doped NIR-CDs were synthesized via a solvothermal method using L-glutathione and formamide, while AuNPs were prepared through a classical citrate-reduction approach. The sensing mechanism is based on an aptamer-regulated inner filter effect (IFE) between NIR-CDs and aggregated AuNPs. In the absence of SA, SA-Apt adsorbs onto the AuNP surface, stabilizing the nanoparticles against salt-induced aggregation and preserving the fluorescence of the NIR-CDs. Upon target recognition, SA-Apt preferentially binds to sarcosine and detaches from the AuNP surface, triggering salt-induced aggregation of AuNPs. This aggregation produces significant spectral overlap with the NIR-CD emission band, resulting in efficient fluorescence quenching via the inner filter effect. The incorporation of NIR-CDs enhances detection sensitivity by providing strong fluorescence emission, minimal background interference, and improved photostability. Under optimized conditions, the NIR-CDs/AuNPs/SA-Apt platform exhibited a linear response to sarcosine over the range of 1–15 µM, with a correlation coefficient (R²) of 0.996 and a limit of detection of 0.32 µM (S/<i>N</i> = 3). The sensing system demonstrates high selectivity, good reproducibility, and stable NIR fluorescence performance. By integrating NIR-emissive carbon dots with plasmonic aggregation and aptamer-mediated regulation, this work provides a robust non-enzymatic strategy for sarcosine detection.</p>