Cationic fluorescent carbon dots with solution ultra-stability and its rapid/on-site sensing application for HClO

Carbon dots (CDs) as a remarkable fluorescent nanomaterial have the advantages of easy preparation, good photostability and high sensitivity. However, the poor aqueous solution stability of carbon dots largely limited their practical application due to the characteristic of easily forming precipitation for long time storage. Here, a kind of cationic fluorescent carbon dots CDs-P(Ph)₃ was designed by introducing a cationic compound, (4-carboxybutyl) triphenyl phosphonium bromide, to construct an electrostatic shell outside the dots. Such electrostatic shell could highly improve carbon dots stability in an aqueous solution to make CDs-P(Ph)₃ stable for long-term storage with negligible aggregation. Meanwhile, the sensitivity of CDs-P(Ph)₃ for hypochlorous acid (HClO) was also enhanced on the basis of the electron-withdrawing effect of cationic substituents on the surface of carbon dots. The limit of detection of CDs-P(Ph)₃ for HClO was as low as ∼0.32 μM. Additionally, the fluorescence of CDs-P(Ph)₃ could be rapid quenched by HClO with a quenching efficiency of more than 80% within 30 s. The excellent stability of CDs-P(Ph)₃ in an aqueous solution made it suitable for on-site detecting HClO in real samples, such as tap, well and lake water. Such designed fluorescent nanomaterial would provide a practical application pathway for optical sensing detection in environmental samples.