Preparation and rapid analysis of antibacterial silver, copper and zinc doped sol-gel surfaces

The colonisation of clinical and industrial surfaces with microorganisms, including antibiotic-resistant strains, has promoted increased research into the development of effective antibacterial and antifouling coatings. This study describes the preparation of metal nitrate (Ag, Cu, Zn) doped methyltriethoxysilane (MTEOS) coatings and the rapid assessment of their antibacterial activity using polyproylene microtitre plates. Microtitre plate wells were coated with different volumes of liquid sol-gel and cured under various conditions. Curing parameters were analysed by thermogravimetric analysis (TGA) and visual examination. The optimum curing conditions were determined to be 50-70 °C using a volume of 200 μl. The coated wells were challenged with Gram-positive and Gram-negative bacterial cultures, including biofilm-forming and antibiotic-resistant strains. The antibacterial activities of the metal doped sol-gel, at equivalent concentrations, were found to have the following order: silver > zinc > copper. The order is due to several factors, including the increased presence of silver nanoparticles at the sol-gel coating surface, as determined by X-ray photoelectron spectroscopy, leading to higher elution rates as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The use of microtitre plates enabled a variety of sol-gel coatings to be screened for their antibacterial activity against a wide range of bacteria in a relatively short time. The broad-spectrum antibacterial activity of the silver doped sol-gel showed its potential for use as a coating for biomaterials.