A Label-Free G-Quadruplex/Thioflavin T Fluorescent Sensor for ClO<sup>-</sup> Detection: Implications for Stress-Induced Hypertension Biomarker Analysis.

Abstract

The objective of this study is to develop a label-free fluorescent sensor for the quantitative detection of hypochlorite ions (ClO^-) and validate its applicability in biological samples, particularly exploring the potential of ClO^- as a biomarker for stress-induced hypertension (SIH). Male Sprague-Dawley rats (8 weeks old, 250-300 g) were used to establish the SIH model. A guanine-rich (G-rich) signal DNA sequence (S-DNA) was rationally designed, with a ClO^--responsive phosphorothioate (PS) moiety integrated into the probe architecture. In the absence of ClO^-, the S-DNA folds into a stable G-quadruplex structure, which specifically binds to ThT and triggers a significant enhancement of the dye's fluorescence intensity. Upon introduction of ClO^-, the specific hydrolysis reaction between the PS moiety and ClO^- induces cleavage of the S-DNA into two discrete fragments, thereby abrogating G-quadruplex formation and resulting in a remarkable quenching of ThT fluorescence. This proposed method exhibits excellent anti-interference capability against other reactive oxygen species (ROS) and achieves a low detection limit of 41.2 nM for ClO^-. Furthermore, this strategy was successfully applied to the quantitative determination of endogenous ClO^- in human cells and the plasma of stress-induced hypertensive (SIH) rats, highlighting its substantial potential for clinical and physiological research.