Parameters Controlling Octadecyl Phosphonic Acid Self-Assembled Monolayers on Titanium Dioxide for Anti-Fouling Biomedical Applications

Titanium is a widely used metal for biomedical applications, however it is prone to bacterial colonisation due to a lack of anti-fouling and antimicrobial properties. Octadecylphosphonic acid (ODPA) self-assembled monolayers (SAMs) have previously demonstrated promising results for deterring bacterial attachment to titanium, however coating processes for phosphonic acids are time-consuming and usually require the use of toxic solvents. In this study, ODPA SAMs were deposited on titanium dioxide (TiO2) quartz crystal microbalance (QCM) sensors using two environmentally eco-friendly solvents (anisole and cyclopentyl methyl ether (CPME), two concentrations of ODPA (0.5mM and 1mM) and two processing temperatures (21°C and 60°C). The quantity, quality, and structure of the ODPA SAMs were characterised using QCM frequency and dissipation measurements and Sauerbrey mass calculations; X-ray photoelectron spectroscopy (XPS); water contact angle measurements; atomic force microscopy and thermal-programmed desorption mass spectrometry (TPD-MS). Incubation in a solution of 0.5 mM ODPA in CPME at RT for 10 minutes resulted in a uniform rigid ODPA SAM as demonstrated by high Sauerbrey mass (≈285-290 ng/cm 2 ), viscoelastic modelling (bandwidth over frequency change at overtones), high atomic percentage phosphorus detected on the surface using XPS (1.1%) and high water contact angles (117.6±2.5°), consistent across the entire sample surface.