Green and structurally tailored synthesis of g-CNQDs for highly selective dopamine detection

A facile and green one-step hydrothermal synthesis of graphitic carbon nitride quantum dots (g-CNQDs) using polyethylenimine (PEI) as a structure-directing agent is reported. The inherent structural features of PEI, including its branched architecture and abundant amine groups, drive a remarkable self-cyclization process that spontaneously generates triazine-based g-CNQDs exhibiting bright blue fluorescence. Unlike traditional synthetic strategies that involve complex procedures and hazardous reagents, our streamlined protocol produces g-CNQDs with a moderate quantum yield, outstanding aqueous dispersibility, and favorable biocompatibility. The resulting g-CNQDs exhibit exceptional sensing capabilities based on electrostatic interactions between their positively charged surfaces and negatively charged dopamine (DA) molecules. Upon binding, a stable non-fluorescent g-CNQDs-DA complex forms, generating a highly sensitive “turn-off” fluorescence response that correlates linearly with DA concentration. The developed probe achieves a low detection limit of 43 nM (S/N = 3) across a wide linear range of 0.1–300 μM. Validation in human urine and serum samples confirms the probe’s high selectivity for DA over potentially interfering biomolecules and metal ions, with recoveries ranging from 97 to 106%. This approach effectively addresses the challenges of green synthesis and selective detection, offering a promising platform for sustainable and specific fluorescent probes in diverse bioanalytical applications.

Graphical Abstract