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 Fe 3+ recognition capacity in contrast to other competing metal ions . Fe 3+ can efficiently quench the fluorescence of CDs even at fairly low concentration (30   μM) with a detection limit as low as 1.68   nM. The fluorescence quenching kinetics are likely to involve static quenching, which is caused by specific interactions between NTSC-CDs and Fe 3+ 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 Fe 3+ in bacillus subtilis. In effect we successfully fabricated an effective fluorescent nanosensor for both the quantitative detection of Fe 3+ in aqueous solutions, and its real-time imaging in vivo.