Khaikate O.Phudphong P.Saiyasombat W.Ouengwanarat B.Wonglakhon T.Kamkaew A.Kuhakarn C.Mahidol University2026-05-152026-05-152026-10-01Dyes and Pigments Vol.253 (2026)01437208https://repository.li.mahidol.ac.th/handle/123456789/116725Cysteine (Cys) and homocysteine (Hcy) are important biothiols that contribute to the maintenance of physiological homeostasis and are closely associated with various diseases. However, their concentrations in living systems are significantly lower than that of glutathione (GSH), which poses a considerable challenge for the selective detection of Cys/Hcy in the presence of abundant GSH. In this work, a 2-mercaptopyridine moiety that serves as both a quencher and a recognition unit was incorporated into an asymmetric heptamethine cyanine scaffold (Cy7-TCF) to create the near-infrared (NIR) fluorescent probe (Cy7-TCF-Spy). The Cy7-TCF-Spy probe enabled selective detection and fluorescence bioimaging of Cys/Hcy. Although the Cy7-TCF-Spy probe displayed negligible fluorescence in its initial state, upon interaction with Cys or Hcy, it exhibited a strong fluorescence emission at 774 nm even in the presence of GSH. The probe also demonstrated high sensitivity toward Cys/Hcy, with respective detection limit of 95 nM and 67 nM, low cytotoxicity, large Stokes shift (104 nm), and fast responsive time (within 1 min). In addition, high resolution mass spectrometry (HRMS) and time-dependent density functional theory (TD-DFT) calculations were performed to elucidate the fluorescence response mechanism of the probe. Importantly, Cy7-TCF-SPy successfully visualized exogenous Cys/Hcy in A549 cells. Furthermore, the probe was capable of detecting Cys in various food samples, including apple, cabbage, celery, carrot, potato, onion, red onion, and Thai whisky, highlighting its practical applicability in food analysis.Chemical EngineeringArticleSCOPUS10.1016/j.dyepig.2026.1138262-s2.0-10503802782418733743