Understanding the Design of Ultrathin Polyzwitterionic Coatings for Anti-Fouling Applications

Polyzwitterions, a unique type of polyampholyte, possess both positive and negative charges on individual monomers, showcasing exceptional antimicrobial and anti-fouling properties. This study presents an innovative approach to chemically attach thin layers of polyzwitterions to solid surfaces, resulting in ultra-thin antimicrobial and anti-fouling coatings. We synthesized a sulfobetaine polyzwitterion, specifically poly(2-vinylpyridine propanesulfonate) (P2VPPS), using free-radical polymerization. A photoreactive benzophenone derivative was then covalently bonded to a SiO₂ substrate via a silane anchor. Ultrathin films of P2VPPS were created through spin-coating and drop-casting techniques on the benzophenone-modified substrate, allowing us to compare thickness variations and antifouling performance across different film thicknesses. A series of films were created with different degree of crosslinking, exposing them to 365nm. These ultrathin films were characterized using X-ray photoelectron spectroscopy, X-ray Reflectometry, contact angle measurements, atomic force microscopy and sum frequency generation methods. The effect of crosslinking on antifouling properties was evaluated by measuring gravimetrically using a quartz crystal microbalance with dissipation and amphiphilic ß casein protein. We will discuss the effect of light-induced crosslinking on the structure and properties of these films, noting that both film thickness and protein retention increase with the increased degree crosslinking.