A G-quadruplex/thioflavin T-based label-free biosensor to detect ClO^- in stress-induced hypertension

Hypochlorous acid (HClO), as an essential reactive oxygen species (ROS) in biological systems, plays a pivotal role in processes of physiology and pathology. Abnormal fluctuations in HClO concentration can lead to various diseases, such as inflammation, cardiovascular diseases, and neurodegeneration. Therefore, developing an approach to rapidly and sensitively quantify ClO^- content is vital to biomedicine development and bioassays. Herein, we fabricated a novel "turn-on" label-free fluorescence DNA probe to specifically detect hypochlorite ion (ClO^-) based on G-quadruplex formation. To this end, we designed a G-rich signal DNA sequence (S-DNA) and a block DNA sequence (B-DNA), followed by the introduction of ClO^--responsive phosphorothioate (PS) into B-DNA. In the absence of ClO^-, B-DNA hybridized with S-DNA, preventing G-quadruplex formation from S-DNA; this resulted in the relatively low fluorescence intensity of ThT. Once ClO^- was added, the hydrolysis between PS and ClO^- split the B-DNA into two fragments, resulting in B-DNA breaking away from S-DNA, allowing G-quadruplex formation from S-DNA and increasing the fluorescence intensity of ThT. Using this method, we can detect ClO^- without the interference of additional reactive oxygen species. The detection limit of ClO^- was as low as 10 nM. Furthermore, this method facilitates the detection of ClO^- within the tissues of rats with stress-induced hypertension.