Design and physico-chemical characterization of metal-containing nanoparticles for antimicrobial coatings
Novel properties of engineered nanomaterials (NMs) (less than 100 nm in at least one dimension) are exploited in numerous consumer products and in product development. Many consumer products aim to prevent the spread of microbes. Silver (Ag) is known for its Ag+ ion-based antimicrobial properties and therefore Ag nanoparticles (NPs) are one of the most used NMs in consumer products. Antimicrobial products are meant to kill or inhibit the growth of predominantly bacteria without causing harm to so-called non-target organisms (including humans) and therefore, the current research includes studies about the antimicrobial efficacy and toxicity to mammalian cells, including the mechanisms behind it, of a library of Ag NPs with different sizes, shapes and surface charges. The results suggest avoiding the use of positively charged Ag NPs in human directed products as those particles presented notably higher toxic effect to mammalian cells. Based on those results, the study made suggestions for using Ag NPs in antimicrobial coatings: the development of which is difficult to underestimate due to the increasing spread of multidrug resistant microbes. Along with Ag NPs, this study suggested including a photocatalytic component to the surface coatings as according to our previous results, photocatalytic coatings have the potential to degrade organic material on their surface. Partially soluble ZnO NPs were chosen as the photocatalytic component. ZnO NPs were supplemented with Ag NPs (ZnO/Ag composite NPs) to prepare efficient antimicrobial coatings with a combined effect from photocatalysis and antimicrobial metal ions (Ag+, Zn2+). The addition of Ag NPs increased photocatalytic effect and antimicrobial efficiency and therefore Ag can be considered a suitable material in the development of efficient photocatalytic material-based antimicrobial coatings. Reusability of the prepared coatings was tested and no significant decrease in neither antibacterial activity nor photodegradation capability was observed after 10 usage cycles. According to our best knowledge, our study was the first to demonstrate the reusability of ZnO/Ag surfaces for antimicrobial applications.