Toxicity Effects Of Graphene Quantum Dots On Zebrafish Embryo

Objective:To evaluate the toxic effects of graphene quantum dots (GQDs) on embryonic development by zebrafish model.Methods:The biodistribution and the developmental toxicities of GQDs were investigated in embryonic zebrafish at exposure concentration ranging from 12.5 to 200μg/mL during 4-96 hours post-fertilization (hpf). Mortality, hatching rate, malformation, heart rate, body length, spontaneous movement, cardiovascular systems of zebrafish embryo were measured. Larval behavior were observed by Noldus tracking device. GQDs uptake were evaluated by fluorescence microscopy and Laser Scanning Confocal Microscopy.Results and Conclusion:(1) The GQDs effect on zebrafish embryo’s development:the hatching rate, heart rate and body length decreased while mortality increased with the exposure concentration. Various embryonic malformations including pericardial edema, vitelline cyst, bent spine and bent tail were resulted from the exposure to high level of GQDs (200μg/mL). The spontaneous movement significantly decreased when zebrafish embryo were exposed to GQDs at the concentration of 50,100,200μg/mL.(2) The GQDs effect on cardiovascular systems of zebrafish embryos:the expression of flk-1, nkx 2.5 and EphrinB2 decreased in a dose-dependent manner. Histopathological examination showed that the numbers of myocardial cells decreased, and ventricular and atrial wall turned to thin in a dose-dependent manner.(3) GQDs uptake and distribution:the zebrafish larve (96 hpf) were observed by fluorescence microscopy. GQDs fluorescence was mainly localized in the heart and intestines without distinguishable fluorescence in the other organs. The GQDs fluorescence was located in the heart area without flowing blood. The histopathological observation showed the distribution of GQDs was mainly in the cytoplasm of myocardial cells by Laser Scanning Confocal Microscopy.(4) The GQDs effect on the alteration of larval locomotor activity:In the visible light, the larval behavior showed that the total swimming distance and swimming speed decreased in a dose-dependent manner. In the light-dark test, zebrafish larva showed hyperactivity when embryos were exposed to 12.5μg/mL, however, a remarkable hypoactivity were observed in higher concentrations (25,50,100,200μg/mL) at 144 hpf.