Carbon quantum dots prepared from onion extract as fluorescence turn-on probes for selective estimation of Zn2+ in blood plasma

Abstract

Zinc is an essential micronutrient. It has significant roles in innumerable biological processes and enzymatic reactions that occur in human body. Deficiency of zinc causes acrodermatitis enteropathica and excess consumption of zinc is responsible for diabetes, cerebral ischemia, epilepsy, neural degeneration, and neurological disorders like Alzheimer’s disease and Parkinson’s disease. Therefore, monitoring of level of zinc in body fluid and tissue may be effective in early detection of diseases. In recent years, cell permeable fluorescent dye-based probes have been reported for sensing intracellular Zn2+ ions but there is no report on development of carbon quantum dot (CQD) for sensing Zn2+ in plasma. In this study CQD of ∼1 nm size was synthesized form onion extract using hydrothermal method. They were quasi-spherical in shape and had lattice stripes due to graphitic core. Particle surface was decorated with polyhydroxy group and amino group. When excited at 325 nm, the presence of Zn2+ ions significantly enhanced the fluorescence intensity in Tris buffer and blood plasma, whereas others common cations like Fe3+, Pb2+, Cu2+, Ca2+, and Hg2+ ions had similar effect in quenching the fluorescence intensity. The quantum yield was 6.214 % and was very much sensitive to the presence of Zn2+ ions. The limit of detection and limit of quantitation values for Zn2+ ions in plasma were 6.4 μM and 21.3 μM respectively. The affinity constant of Zn2+ to CQD was 600 M−1 whereas the association constant was 185 M−1.