A novel pH probe based on tetrahydropyridine synthesis and its application in bioimaging

Abstract

Half-cyanine dye is a highly tunable red fluorescent structure, with fluorescence emission in the near-infrared region (650 nm–900 nm). This study utilized nitrogen substituted –CH₂ to design and synthesize a cyanine structure with a tetrahydropyridine ring. Based on the characteristics of this structure, a novel fluorescent probe He-Cy was designed and synthesized, capable of detecting pH levels effectively. Through an in-depth analysis of the structural and optical properties of the He-Cy probe, it was found that the difference in UV absorption in different pH environments mainly originated from the internal charge transfer (ICT) effect induced by the protonation and deprotonation of hydroxyl groups. The fluorescence intensity of this probe increases with pH showing excellent photostability and biocompatibility. As demonstrated in cell and zebrafish models, the He-Cy probe was able to respond to a variety of exogenous pH changes. Specifically, pH 7.12 brought about a significant increase in luminescence brightness, whereas acidic pH brought about a decrease in luminescence brightness. This property suggests that the He-Cy probe can effectively monitor pH changes in biological microenvironments. There is a broad scope of applications for the He-Cy probe, which is expected to contribute significantly to biomedical research and clinical diagnosis.