Preparation of an Efficient Ratiometric Fluorescent Nanoprobe (m-CDs@[Ru(bpy)₃]²⁺) for Visual and Specific Detection of Hypochlorite on Site and in Living Cells

Hypochlorite (ClO–) is one of the most important reactive oxygen species (ROS), which plays an important role in sustaining human innate immunity during microbial invasion. Moreover, ClO– is a powerful oxidizer for water treatment. The safety of drinking water is closely related to its content. Herein, m-phenylenediamine (mPD) is used as a precursor to prepare carbon dots (named m-CDs) with highly fluorescent quantum yield (31.58% in water), and our investigation shows that the strong fluorescent emission of m-CDs can be effectively quenched by ClO–. Based on these findings, we developed a novel fluorescent nanoprobe (m-CDs) for highly selective detection of ClO–. The linear range was from 0.05 to 7 μM (R2 = 0.998), and the limit of detection (S/N = 3) was as low as 0.012 μM. Moreover, a portable agarose hydrogel solid matrix-based ratiometric fluorescent nanoprobe (m-CDs@[Ru(bpy)3]2+) sensor was subsequently developed for visual on-site detection of ClO– with the naked eyes under a UV lamp, suggesting its potential in practical application with low cost and excellent performance in water quality monitoring. Additionally, intracellular detection of exogenous ClO– was demonstrated via ratiometric imaging microscopy.