Synthesis of photoluminescent carbon dots for the detection of cobalt ions

We have developed a simple assay for the sensing of cobalt ions (Co²⁺), based on the analyte induced photoluminescence (PL) quenching of carbon dots (C-dots). The C-dots (mean diameter 3.6 ± 0.3 nm) prepared from l-cysteine through a simple hydrothermal process at 300 °C for 2 h have a quantum yield of 13.2%. The C-dots have strong blue PL with a maximum PL intensity at 395 nm under an excitation wavelength of 325 nm. Through the reactions of Co²⁺ ions with cysteine molecules/residues on the surfaces of the C-dots, non-photoluminescent Co_xS_y nanoparticles are formed. As-formed Co_xS_y nanoparticles and the C-dots further form aggregates in the solution, leading to PL quenching. The C-dot probe allows detection of Co²⁺ ions over a concentration range from 10 nM to 100 μM (R² = 0.992). This reliable, rapid, sensitive, and selective C-dot probe has been utilized for the determination of the concentrations of Co²⁺ ions in vitamin B₁₂ and natural water samples.