Superb hydroxyl radical-mediated biocidal effect induced antibacterial activity of tuned ZnO/chitosan type II heterostructure under dark

摘要

Reactive oxygen species (ROS) is the most dominating factor for bacteria cell toxicity due to release of oxidative stress. Hydroxyl radical ((OH)-O-center dot) is a strong oxidizing ROS that has high impact on biocidal activity. This present paper highlights (OH)-O-center dot influenced antibacterial activity and biocidal propensity of tuned ZnO/chitosan (ZnO/CS) nanocomposite against Pseudomonas putida (P. putida) in the absence of light for the first time. For this purpose, the CS proportion was increased by 25 (w/w) of ZnO during the preparation of ZnO/CS nanocomposite and a systematic study of different ROS like superoxide anion (O-2(center dot-)), hydrogen peroxide (H2O2) and (OH)-O-center dot production as well as their kinetics was carried out both under UV irradiation and in dark by UV-Vis spectroscopy using NBT dye, starch and iodine reaction and fluorescence spectroscopy using terephthalic acid. The decoration of ZnO nanoparticles (ZnO center dot NPs) with CS tuning was characterized by XRD and FTIR spectroscopy, revealing sustained crystallinity and surface coating of ZnO NP (size about similar to 24 nm) by CS molecule. The hybridization of ZnO nanoparticles with CS@50 wt (w/w) resulted superior biocidal activity (81 ) within 3 h in dark mediated by optimum production of (OH)-O-center dot among all ROS. Here we have proposed the enhanced production of (OH)-O-center dot in ZnO/CS due to generation of holes by entrapment of electrons in acceptor level formed in nanocomposite for the first time, and the acceptor levels were probed by Positron annihilation lifetime spectroscopy. The increase in non-positronium (non-Ps) formation probability (I-2) in ZnO/CS nanocomposite confirmed the acceptor levels. This work also confirms surface defect-mediated ROS generation in dark, and zinc interstitials are proposed as active defect sites for generation of holes and (OH)-O-center dot for the first time and confirmed by steady-state room temperature photoluminescence spectroscopy. Finally, a plausible mechanism was hypothesized focusing on hole generation in ZnO NP and hole transfer from CS for the first time, and a heterostruc-ture of type II was proposed.