Antibacterial surfaces produced by liquid flame spray deposition of silver nanoparticles

Healthcare associated infections (HAIs) are one of the major problems of modern healthcare. Pathogenic bacteria responsible for these HAIs are mostly transmitted via surfaces. Emphasis on preventive measures can cumulatively reduce associated costs and mortality related to HAIs. Antibacterial surfaces within healthcare settings have been considered as one of the approaches to reduce HAIs. Therefore, further development and wide use of antibacterial surfaces in healthcare settings could be a step that helps to significantly reduce the problem. Nanoparticles (NPs), plant extracts and other inorganic substances have been used for the production of antibacterial surfaces. Particularly, silver nanoparticles (AgNPs) have been shown to have broad-spectrum antibacterial properties, which has resulted in its wide use for fabricating antibacterial products. NP production methods have also evolved continuously, but a production method that allows for continuous synthesis of NPs and their deposition on surfaces had been elusive until the development of Liquid Flame Spray (LFS). LFS enables high speed NP deposition without effluents, and it is suitable for producing large-area antibacterial surfaces. In this project, LFS was used to deposit AgNPs onto paper, glass and fabrics to produce antibacterial surfaces. After NP deposition, scanning electron microscopy and atomic force microscopy (AFM) were used to visualize the samples. Surface chemical characterization was done using x-ray photoelectron spectroscopy, and silver leaching tests were analyzed using inductive coupled plasma-mass spectroscopy. NP adhesion to substrates was improved using thin plasma polymer coating layer, as well as Al2O3 produced by atomic layer deposition. Antibacterial properties were examined using a newly developed ‘Touch Test’ method, which simulates the transfer of bacteria from one surface to another by touch. Imaging results showed that nanoparticles are produced, and multiple flame passes result in the deposition of more AgNPs on sample surfaces. AFM scratch testing in contact mode confirmed results of improved NP adhesion by plasma coating. Antibacterial action against E. coli, S. aureus, and other bacteria was demonstrated, and in the case of E. coli, also for samples that had a thin layer of plasma coating on top of AgNPs. The exact mechanism of the antibacterial effect from below the plasma coating requires further investigation, since usually a direct contact to AgNPs is assumed to be a prerequisite. However, the results of this study suggest that a thin immobilizing layer can be used to improve the adhesion of AgNPs to substrates and to limit their exposure to environment, while still maintaining the desired antibacterial properties.