Ultrasonic-Assisted Synthesis of N-Doped, Multicolor Carbon Dots toward Fluorescent Inks, Fluorescence Sensors, and Logic Gate Operations.

Over past decades, the multicolor carbon dots (M-CDs) have attracted enormous attentions due to their tunable photoluminescence and versatile applications. Herein, the nitrogen-doped (N-doped) M-CDs including green, chartreuse, and pink emissive CDs are successfully synthesized by ultrasonic treatment of kiwifruit juice with different additive reagents such as ethanol, ethylenediamine, and acetone. Owing to their strong fluorescence upon irradiation with 365 nm UV light, the highly water-soluble M-CDs present great potential in the anticounterfeit field as fluorescent inks. Particularly, the resulting green emission CDs (G-CDs) with excellent fluorescence and stability are applied as a label-free probe model for "on-off" detection of Fe. The fluorescence of G-CDs is significantly quenched by Fe through static quenching. The nanoprobe demonstrates good selectivity and sensitivity toward Fe with a detection limit of ~0.11 μM. Besides, the quenched fluorescence of G-CDs by Fe can be recovered by the addition of PO or ascorbic acid (AA) into the CDs/Fe system to realize the "off-on" fluorescent process. Furthermore, NOT and IMPLICATION logic gates are constructed based on the selection of Fe and PO or AA as the inputs, which makes the G-CD-based sensors utilized as various logic gates at molecular level. Therefore, the N-doped M-CDs hold promising prospects as competitive candidates in monitoring the trace species, applications in food chemistry, anticounterfeit uses, and beyond.