A novel and ultrasensitive fluorescent probe derived from labeled carbon dots for recognitions of copper ions and glyphosate.

Labeling materials with special functional groups are very valuable for the creation of novel probes. Hence, a novel fluorescent probe was constructed by conjugating 4-butyl-3-thiosemicarbazide (BTSC) with carbon dots (CDs). The CDs labeled by BTSC (BTSC-CDs) displayed a strong capability for recognition of Cu2+ and Cu2+ could quench the emission of BTSC-CDs significantly. The fluorescence quenching was proved to be a static quenching which was resulted from the interaction between BTSC-CDs and Cu2+ to form a ground-state BTSC-CDs/Cu2+complex, and the fluorescence intensities showed a good linear correlation with Cu2+ concentrations in the range of 0.20-30 µM. What is more important, by adding glyphosate into the sensor system of BTSC-CDs/Cu2+ the fluorescence of the probe turned on again owing to the stronger chelating between glyphosate and Cu2+ than between BTSC-CDs and Cu2+. This could realize the specific detection of glyphosate and the limit of detection was low to 0.27 µM. Detecting glyphosate using the complex BTSC-CDs/Cu2+ system in actual samples with satisfactory outcomes indicated that a novel fluorescent probe for Cu2+ and subsequent glyphosate detections has been provided.

Utilizing the interfacial reaction of naphthalenyl thiosemicarbazide-modified carbon dots for the ultrasensitive determination of Fe (III) ions.

Since thiosemicarbazide contains numerous nitrogen and sulfur atoms in its structural formula that enhance its strong coordinating abilities with metal ions, it is always selected as the mother molecule for the design of metal-ion sensors. In this report, a thiosemicarbazide derivative (4-naphthalenyl-3-thiosemicarbazide (NTSC)) was synthesized via a single step process and covalently conjugated onto the surfaces of carbon dots (CDs). The modified CDs demonstrated excellent monodispersity, good photostability, and tunable luminescence properties. More importantly, the CDs retained a highly specific Fe3+ recognition capacity in contrast to other competing metal ions. Fe3+ can efficiently quench the fluorescence of CDs even at fairly low concentration (30µM) with a detection limit as low as 1.68nM. The fluorescence quenching kinetics are likely to involve static quenching, which is caused by specific interactions between NTSC-CDs and Fe3+ toward the formation of a ground state complex. Due to their excellent optical performance, low toxicity, and good biocompatibility the NTSC-CDs may be applied to the imaging and monitoring of Fe3+ in bacillus subtilis. In effect we successfully fabricated an effective fluorescent nanosensor for both the quantitative detection of Fe3+ in aqueous solutions, and its real-time imaging in vivo.