Dopant-Driven Metal Ion Response in Carbon Dots: The Role of Excitation Wavelength in Selective Sensing and Potential Design of an Eco-Friendly ATP Sensor

In this study, nitrogen- and boron-doped carbon dots (CDs) were synthesized via a microwave-assisted method and evaluated for metal ion sensing and ATP detection. The work investigated how surface and core states influence photophysical behavior and selective quenching. FTIR confirmed distinct carboxyl, amine, and hydroxyl surface functionalities for each CD variant. Spectroscopic analysis revealed excitation-dependent emissions, linking specific radiative transitions to functional groups and core states. Notably, Cu²⁺ quenched 80% of fluorescence primarily at shorter excitation wavelengths (300 nm), indicating strong surface-state interactions, while Ag⁺ induced 65% quenching at longer wavelengths (450 nm) through core-state interactions. Boron-doped CDs displayed at least a 20-fold fluorescence enhancement upon exposure to Mg²⁺, Zn²⁺, and Cd²⁺ at 300 nm, attributed to surface passivation. In ATP sensing assays, the CDs’ high sensitivity to Cu²⁺ and ATP's affinity for copper ions enabled detection via absorption and fluorescence spectroscopy. These results demonstrate that tuning excitation wavelength modulates sensor selectivity, showing doped CDs as cost-effective, eco-friendly platforms for wavelength-specific ion and biomolecule detection. The combined quenching and enhancement behaviors emphasize the critical role of surface and core state engineering in achieving wavelength-specific responses. This study provides a foundation for developing low-cost, environmentally friendly sensors based on doped CDs with tunable selectivity.