Blue-LED assisted Photodegradation kinetics of rhodamine-6G dye, enhanced anticancer activity and cleavage of plasmids using Au-ZnO nanocomposite

The plasmonic metal doping on the UV-active metal oxide nanoparticle turns the resultant plasmonic metal-metal oxide (PMMO) into visible light active and upon exogenous illumination the photogenerated energetic charge carriers and the <i>in situ</i> generated reactive oxygen species (ROS, e.g. ·OH and O₂ ^-·) authoritatively enhances its biological and catalytic activity. Herein, a hexagonal rod-shaped ZnO nanoparticles (NP) precursor was prepared using the sol-gel method, which in the presence of varying concentrations of gold (0.005M, 0.01M, and 0.015M) <i>via</i> a greener citrate reduction method afforded a nanocrystalline Au-ZnO nanocomposite. Using which, the visible-light driven photo-degradation kinetics investigation of rhodamine-6G (R6G) dye under blue LED irradiation were carried out. The use of 20 mg 0.015-Au-ZnO completes the degradation of R6G (97.0 %, k = 6.5 X 10^-3s^-1 at pH 7) within 55 min while 50 mg of 0.015-Au-ZnO catalyst improves the rate of R6G degradation (15 min 97.8 %, k = 14.8 × 10^-3 s^-1) and it is reusable up to three cycles. The LC-MS spectra of the remains of R6G (after 15 min) identified various low molecular ions (up <i>m</i>/<i>z</i> = 65). Further, the blue-LED assisted anti-cancer studies (MTT assay) using 0.015-Au-ZnO towards human lung cancer cells (A549), breast cancer cells (SKBr3) show high anti-proliferation rate and low cytotoxicity against healthy human embryonic kidney cells (HEK-293) with an IC₅₀ value of 65, 53 and 124 μg/mL respectively. Also, the AO-EB dual staining and DCFH-DA analysis of SKBr3 and A549 cells revealed ROS-mediated cell death <i>via</i> apoptosis. Moreover, plasmid cleavage studies against supercoiled pBR322 DNA result in single-stranded linear DNA without traversing the nicked circular form, suggesting the possible DNA targeting activity of Au-ZnO nanozyme. Thus, the synthesized Au-ZnO nanocomposite shows excellent photocatalytic and biological activity.