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

Abstract

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.