Affinity-mediated photoluminescence quenching between metallic ions and surface functional groups of carbon nanodots

Carbon nanodots (C-dots) have been widely employed to detect metallic ions based on photoluminescence (PL) quenching. Nonetheless, the selectivity of detection is still dissatisfactory. This is due to the lack of sufficient knowledge on metallic ions quenching the PL of C-dots. Herein, affinity-mediated PL quenching between metallic ions with carboxyl- and hydroxyl-covered C-dots is revealed. The PL results showed that both Fe2+ and Fe3+ can quench the PL of C-dots, but the PL quenching kinetics are totally different. The carboxyl groups are demonstrated to preferentially coordinate with Fe3+ because of the high affinity between Fe3+ and carboxyl groups, while Fe2+ preferentially binds to hydroxyl groups. In addition, the PL quenching of two C-dots prepared by glucose and carbon fiber powder was further investigated after being treated with various metallic ions, confirming that the PL quenching depended on the affinity between metallic ions and the surface functional groups of C-dots. This study provided a better understanding of the PL quenching mechanism of C-dots by metallic ions and will contribute to the rational design of high specificity and selectivity C-dots-based sensors for discrimination of metallic ions in complex matrix samples.