Polyethylene glycol functionalization modulates the toxicity of zinc oxide quantum dots: a multilevel characterization and toxicological study of Channa punctatus Bloch.

Quantum dots (QDs), especially metal oxide QDs, possess properties such as size-tunable band gaps and a high surface-to-volume ratio that are exceptionally advantageous in biomedical applications. In this study, we synthesized zinc oxide quantum dots (ZnO-QDs) and polyethylene glycol (PEG) functionalized ZnO-QDs (PFQD) and characterized them using transmission electron microscopy, UV-vis absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. An in vivo acute toxicity analysis of ZnO-QD and PFQD was conducted over 96 h. The LD50 values for both the ZnO-QD and PFQD were 144.082 and 225.246 µg/g b.w., respectively. Following the acute toxicity assessment, a sub-acute toxicity test was conducted to assess the effects on bioaccumulation, as well as hematological, histological, and enzymatic parameters, oxidative responses, and genotoxicity in fish. This was achieved by administering 1/50 of the LD50 values of the acute dose to fish, alongside a control group, over 14 days. PFQD relative to the ZnO-QD nanoparticles showed significantly lower bioaccumulation of Zn levels (ppm/g) in both liver and head kidney tissues (p < 0.05). ZnO-QD exposure reduced erythrocyte count, hemoglobin levels, and hematocrit, with increased leukocyte and platelet counts, while PFQD caused fewer hematological alterations. According to serum biochemical indicators, ZnO-QD exposure caused hepatic and renal damage, inflammation, histopathological changes, and an apoptotic assay (as determined from DNA laddering and DAPI Annexin V-FITC staining), contrasting with PFQD. In the liver and kidney, macrophages (Kupffer and mesangial cells) showed that ZnO-QDs enhanced lipid peroxidation and significantly lowered antioxidant defenses. In contrast, PFQD decreased LPO and increased antioxidant enzyme activity. In conclusion, this study suggests that PFQD exhibits superior radical scavenging capabilities, positioning it as a potential antioxidant and a better biocompatible agent.