Development of a ratiometric N-CDs/RhB fluorescent probe for selective and sensitive detection of arginine and ascorbic acid.

Arginine (Arg) and ascorbic acid (AA) are essential nutrients that significantly impact human health. In this research, we introduced a novel N-CDs/RhB ratiometric fluorescent probe for sensitive detection of Arg and AA. The probe was constructed through simple physical mixing of rhodamine B (RhB) and nitrogen-doped carbon dots (N-CDs), leveraging fluorescence resonance energy transfer (FRET) between N-CDs and RhB. The optimal excitation wavelength for N-CDs was determined to be 440 nm, with fluorescence emission at 510 nm, while RhB exhibited excitation and emission peaks at 557 nm and 572 nm, respectively. The N-CDs/RhB probe demonstrated excellent stability across various pH values and salt concentrations, and under UV light exposure, allowing reliable performance under diverse conditions. The probe exhibited high selectivity and anti-interference properties, with no significant response to other amino acids or food additives. Its response to Arg and AA was characterized by an "on-off-on" mechanism, with fluorescence quenching upon the addition of Arg due to electrostatic adsorption and static quenching, and fluorescence recovery upon the addition of AA through a redox reaction that weakened the guanidinium-carboxylate bridge interaction. The probe demonstrated linear detection ranges of 0.7-60 µM for Arg and 7.7-220 µM for AA, with detection limits of 0.21 µM and 2.32 µM, respectively. Real-world testing in functional beverages further confirmed the practical applicability of the probe, with recovery rates for Arg and AA ranging from 97.44% to 100.83%. These results highlight the potential of the N-CDs/RhB ratiometric fluorescent probe for real-time, precise sequential detection of Arg and AA in complex samples.