Optically tunable fluorescent carbon nanoparticles and their application in fluorometric sensing of copper ions

A series of carbon nanoparticles (CNPs) with emission wavelength ranging from 483 to 525 nm were prepared by hydrothermal treatment of poly-3-thiopheneacetic acid (PTA) and NaOH. The emission wavelength and surface oxidation degree of CNPs were shown to be controllable by simply adjusting NaOH concentration. These CNPs presented obvious fluorescence spectral response toward copper ions (Cu²⁺) through static quenching caused synergistically by electron transfer and inner filter effect. The O- and S-containing groups on the surface of CNPs were demonstrated to be responsible for their outstanding sensing performance. Based on that, a CNPs-based ratiometric fluorescent probe for Cu²⁺ with a high fluorescence quenching rate constant of 1.4 × 10⁵ L/mol and a short response time (10 s) was developed. Their practical applications in detecting Cu²⁺ in pond water and living cells were also demonstrated.