Carbon dots with red emission for bioimaging of fungal cells and detecting Hg2+ and ziram in aqueous solution

Abstract It is of importance for bioimaging of fungal cells using biocompatible and low toxic carbon dots (CDs) as labels in plant protection field because a clearer understanding on the infection mechanism of fungi on plant can be achieved. Meanwhile, long wavelength, especially, red/near-infrared (NIR) emissive CDs are more biocompatible than short wavelength emissive ones. In this work, CDs with red emission were synthesized by solvothermal pyrolysis of citric acid, acrylamide dissolved in formamide. Fungal cells stained by the CDs with red emission were brightly illuminated when imaged on a fluorescent microscope with excitation by a green laser pulse, suggesting the CDs are of an excellent label for bioimaging of fungal cell in red color region. Moreover, the CDs show a selective response to Hg2+ in the NaAc–HAc buffer solution, while ziram can form a more stable complex with Hg2+, leading to a recovery of the quenched fluorescence of the CDs. Therefore, methods for the detections of Hg2+ and ziram based on the “off-on” fluorescence of the CDs were established with limits of detection as low as 0.19 μM and 0.55 μg/mL.