Nanosize and shape effects on antimicrobial activity of silver using morphology-controlled nanopatterns by block copolymer fabrication

Abstract

The activity of silver nanomaterials as an antimicrobial is well-known with authors noting strong size and shape effects. This paper explores if the antimicrobial activity relates to unique size-related properties of the nanodimensioned materials or a more physical effect. Staphylococcus aureus and Pseudomonas aeruginosa were explored as test bacteria. They can cause serious human infections and are becoming resistant to pharmaceutical antimicrobials. Silver nanopatterns on a substrate surface were used as the antimicrobial agent. We demonstrate a cost-effective facile route to fabricate a well-ordered, periodic, and dimension-controlled silver lines and dots pattern on a substrate surface. This allowed precise definition of the silver materials to explore size and shape effects. Polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) microphase separated thin films were used as structural templates. Well-ordered PS-b-PEO thin film with vertical and parallel oriented PEO cylinders was achieved by a solvent vapor annealing approach through careful optimization of experimental parameters. A selective inclusion method (into one block of the BCP) of silver nitrate was used to generate the silver nanopatterns. Spin coating precursor-ethanol solution and subsequent UV/ozone treatment produce silver nanopattern arrays. They exhibited a significant growth-inhibitory effect on Staphylococcus aureus and Pseudomonas aeruginosa biofilms. However, data suggest this is associated with high surface area rather than a unique nanodimension related property change dictated by size or shape.