Facile and Green Synthesis of Bifunctional Carbon Dots for Detection of Cu²⁺ and ClO^– in Aqueous Solution

Devising novel water-soluble carbon dots (CDs) with a facile and economical process is pivotal for the detection of ions in the environment. In this paper, novel nanoscale CDs (polyethyleneimine-2,4-dihydroxybenzoic acid (PEI-DA)) with water solubility and bifunctional detection were synthesized from hyperbranched polyethyleneimine (hPEI) and 2,4-dihydroxybenzoic acid (DA) via a hydrothermal reaction and further self-assembly. PEI-DA exhibited a good linear relationship with Cu²⁺ or ClO^– in the range of 0–30 μM, and its detection limit was determined to be 193 nM (Cu²⁺) or 478 nM (ClO^–). Meanwhile, PEI-DA presented excellent hypotoxicity and biocompatibility in living cells (HeLa cells). On the basis of extraordinary fluorescence properties, PEI-DA-doped solid sensors (test strips and nanofibrous films) were successfully employed to monitor targets sensitively. More importantly, the fluorescence hydrogel was further constructed to rapidly respond to targets (Cu²⁺ and ClO^–), and it could effectively remove Cu²⁺ in aqueous solution through adsorption ability. In summary, these simple sensing techniques could be implemented as effective tools to monitor Cu²⁺ and ClO^– in environmental and biological samples.