Synthesis and characterization of palladium nanoparticles by varying size, shape and synthetic approach: A comparative risk assessment study in-vitro as a step towards the development of safe and sustainable nanotechnology

Abstract

The vigorous growth in the equipment of palladium in the autocatalytic converters for mitigating air pollution has led to the release of airborne palladium micro- and nano-particulates in the environment, thus, consequently exposing the occupational workers and urban population to Pd particles, in both fine and ultra-fine fractions. Pd-NPs have been shown to exert cytotoxic and pro-inflammatory effects on the in-vitro and in-vivo models, however, the influence of size, shape and synthetic route on the immunotoxic potential of Pd-NPs is not known yet. Therefore, in this first report, we synthesized Pd microparticles (Pd-MPs), spherical-shaped Pd-NPs via the chemical route (reverse micelle/microemulsion method) and green route using Cannabissativa L. leaf extract (CS–Pd-NPs) and Pd nanorods (Pd-NRs). Characterization techniques such as UV-VIS spectroscopy, TEM, size distribution analysis and FT-IR spectroscopy were used. Further, synthesized particles of environment-relevant concentration were exposed to macrophage cell lines and their cytotoxicity was assessed by MTT assay, Annexin V FITC apoptosis assay and ELISA. Results showed dose-dependent cytotoxicity exerted by all particles when exposed to macrophage cell lines. Among these, Pd-MPs of size ⁓218 nm were found to have the highest cell viability whereas spherical-shaped Pd-NPs of size ⁓4 nm were found to be the least viable as compared to other particles at all concentrations. Apoptosis induced by all the particles was not found to be significant (<3%). ELISA studies showed a minimal rise in TNF-α and IL-6 cytokine levels as compared to control whereas Pd-MPs and CS-Pd-NPs had an insignificant effect on the markers. Through this study, we also gain an insight into the exact size and shape that have the least toxicity for their future applicability in biomedical, industrial and environmental fields to ensure safe and sustainable nanotechnology and environmental safety from their use.