Induced toxicity in early-life stage zebrafish (Danio rerio) and its behavioral analysis after exposure to non-doped, nitrogen-doped and nitrogen, sulfur-co doped carbon quantum dots

In this study, the effects of doping of CQDs with alternative functional groups (dopants) were evaluated through embryonic development of zebrafish (Danio rerio). The CQDs were synthesized using simple and low-cost sources: Non-doped (citric acid was used as the carbon source), nitrogen-doped (N-doped) and nitrogen, sulfur co-doped (N,S-doped). The CQDs induced significant toxicity to zebrafish (150 mu g/mL) and the toxic effects were dose-dependent. The N,S-doped CQDs were the most toxic (LD50 = 149.92 mu g/mL), followed by the N doped CQDs (LD50 = 399.95 mu g/mL) while the non-doped CQDs were the least toxic (LD50 = 548.48 mu g/mL) of the three. The growth rate (GR) was affected following the toxicity pattern (GR(NS-doped) < GR(N-doped) < GR(non-doped) < GR(blanc)), which, in turn, greatly depends on the type of dopant. Morphological malformations, such as pericardial edema, yolk sac edema, tail and spinal curvature were observed to zebrafish embryos as the toxicity, concentration and exposure time to the nanomaterial increased. Behavioral analysis showed that locomotor activity increases as the toxicity of the nanomaterial rises. The differences in toxicity, growth rate and malfunctions of CQDs were attributed to their doping with different heteroatoms. The N,S-doped CQDs, unequivocally, exhibited the most pronounced effects.