Synthesis of fluorescent carbon nanoparticles as selective and sensitive probes for copper ions

A novel sensing system has been designed for the detection of copper ions (Cu2+). It is based on the quenched fluorescence signal of carbon nanoparticles (CNPs), which were carbonization from polyvinylpyrrolidone and L-cysteine. Cu2+ can be captured by the nitrogen and sulfur groups of the CNPs to form an absorbent complex at the surface of CNPs; this results in strong quenching of the CNPs’ fluorescence via a fast metal-to-ligand binding affinity. The resulting water-soluble CNPs also exhibited a quantum yield of 7.6%, with favorable photoluminescent properties and good photostability. Importantly, the fluorescence intensities of the CNPs were quite stable in high ionic strength (up to 1.0 M NaCl) and over a broad range of pH levels (2.0–12.0). This facile method can therefore develop a sensor that offers rapid, reliable, and selective detection of Cu2+ with a detection limit as low as 0.15 μM and a dynamic range of 0.5–7.0 μM (R2 = 0.980). This sensing system was also successfully applied to determine Cu2+ in a lake water sample with satisfactory recovery levels.