A one-step sonochemical synthesis of stable ZnO-PVA nanocolloid as a potential biocidal agent

One of the limitations in the applications and commercialization of metal oxides in diverse fields is their inferior colloidal stability. The ability of metal oxide nanoparticles (MONPs) to remain in the suspended form for long duration is influenced by the particle size and the capping efficiency of the surfactant employed. Among the metal oxides, ZnO is exploited as an effective biocidal agent. For practical applications, the incorporation of ZnO into liquids using a stabilizer is of importance, and therefore synthesizing nanoparticles with high dispersity in solution still remains a challenge. The present work is aimed at synthesizing ZnO nanoparticles (NPs) in colloidal form with great stability, minimal particle size and high antibacterial activity. Herein, we report a single step synthesis of ZnO colloids in aqueous medium by using a biocompatible polymer PVA (poly(vinyl alcohol)) as a stabilizing agent. Both ZnO (without PVA) and ZnO-PVA NPs are prepared using ultrasonic irradiation and their differing particle sizes, stabilities and antibacterial activities are correlated. ESR measurements reveal that ZnO NPs of reduced particle size (∼5 nm) produced increased levels of reactive-oxygen species (ROS). The biocidal effect of the colloidal solution was examined on two bacterial species: Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The results revealed an enhancement in the antibacterial activity for the ZnO-PVA nanofluid.