Green synthesis of carbon dots for ultrasensitive detection of Cu2+ and oxalate with turn on-off-on pattern in aqueous medium and its application in cellular imaging

Herein, spirulina algae were used for synthesizing green fluorescent-carbon dots (G-CDs) due to their featured properties and compatibility in the environment. New G-CDs-based fluorescent probes have been synthesized through a facile hydrothermal method, and various techniques were employed to characterize chemical compositions, physical and optical operations of G-CDs. The G-CDs exhibited an optimal emission wavelength at 520 nm with an exaction wavelength at 450 nm, and quantum yield was found to be 32%. Remarkably, the intensity of fluorescence G-CDs could be selectivity and rapidly quenched by copper (II) ion (Cu2+), with the limit of detection of (LOD) 11.9 nM and a linear range of 0.01–0.1 μM. Meanwhile, upon adding oxalate (C2O42−) into the solution, the fluorescence intensity of G-CDs was restored. The LOD for C2O42− detection was estimated to be 3.5 μM with the concentration in the range of 0–45 μM. Furthermore, the designed fluorescent probe has been successfully utilized for the detection of Cu2+ in tap and mineral water as well as for biosensing of Cu2+ in living cells without surface modification.