Determination of antibacterial effect of CuO and ZnO containing sol-gel surface coatings

It is desirable that surface coatings, such as hospital furniture, walls, food equipment and many others, have antibacterial properties. The aim of the research was to determine the antibacterial effect of a sol-gel derived coatings on stainless steel containing CuO and ZnO. A total of 68 different sol-gel surface coatings on AISI 304 steel (10x3 mm) where examined. 36 containing CuO, and 32 ZnO containing sol-gel compositions were deposited onto polished and phosphated stainless steel (SS) surfaces. Coatings contained 0,5, 1, 3, 5 weight % CuO or 5 and 10 weight % ZnO. Single and multilayered coatings were analyzed. A number of deposited layers were 1, 3, 5 for CuO containing coatings, and  1, 5 for ZnO containing coatings.  Differentially aged sol-gel coating solutions were used to obtain dip-coating compositions. The antibacterial effect was determined to all samples with novel dried droplet method using E.coli 25922 and S.aureus 6538 strains. Only a few of CuO containing materials had an antibacterial effect more than 50% against S.aureus and E.coli. None of the materials containing ZnO showed more than 50% effect against S.aureus. ZnO containing coatings deposited onto phosphated SS surface showed effect more than 99% against E.coli and more than 95% against S.aureus. Dried droplet method is appropriate to determine the antibacterial effect of small-sized materials. It offers a quick and simple way to ascertain antibacterial effects against prospected surfaces samples. CuO sol-gel surface coatings don’t have a noteworthy antibacterial effect. A few of ZnO coatings showed a significant antibacterial effect only against E.coli but not S.aureus. Coatings deposited onto phosphated SS surfaces show much higher antibacterial effect than coatings deposited onto polished SS with some reaching almost 100% effect. Sol-gel surface coatings show potential to be studied in future to determine optimal concentration and preparation for antibacterial surface coating.