Biocompatibility of Kaffir lime fruit juice powered ZnO nanoparticles in earthworm, Eudrilus eugeniae: A green biomimetic approach

ZnO nanoparticles were synthesized using the raw juice of Kaffir lime (Citrus hystrix) fruit bya simple and cost-effective green route and its effects on earthworms, Eudrilus eugeniae, were studied. The kaffir-lime powered ZnO nanoparticles (ZnO:KL) were characterized by X-ray diffraction (XRD), UV-Vis-NIR spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The filter paper method was adopted to test the toxicity of ZnO:KL. Earthworms (species Eudrilus eugeniae) were exposed to 100 to 1000 mg/L of ZnO:KL in one-step order. During the study period (up to 48 h), no mortality was found in any treatment group. In histological observation, no damage was found in the epidermal layer of earthworm’s skin treated up to 800 mg/L, whereas slight epidermal damage was observed only in 900 and 1000 mg/L treated earthworms. The GC-MS spectrum of the juice of kaffir lime fruit revealed 22 bioactive compounds. The predominantly identified bioactive compounds vitamin C and citric acid were subjected to molecular docking to reveal their binding affinity with collagen – a structural protein providing strength and flexibility of the earthworm’s body. Vitamin C and citric acid bind to the collagen in a favorable orientation with the binding affinity of -4.44 kcal/mol and -4.97 kcal/mol, respectively. Since vitamin C and citric acid are capable of influencing the biosynthesis of collagen, they could prevent skin damage. In sum, the kaffir lime-powered ZnO nanomaterial is less toxic to the earthworm when compared with bare ZnO.