Stability of UV/ozone-treated thermoplastics under different storage conditions for microfluidic analytical devices

Thermoplastics are becoming a popular material for fabricating microfluidic devices and there is an increasing need for robust surface modification strategies. UV/ozone (UVO) treatment is a simple and effective method for making plastic surfaces more hydrophilic. Prior reports on the stability of UVO-treated plastics are limited to four weeks, which is not sufficient for applications requiring long-term storage. Here, we present new findings on the long-term stability of UVO-treated plastics for up to 16 weeks and show that the storage condition has a significant impact on the surface stability. Static contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were performed on UVO-treated cyclic olefin copolymer (COC), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) stored in air, dehumidified and vacuum conditions. We found that the hydrophobic recovery of UVO-treated COC and PC can be inhibited by storing them in dehumidified or vacuum conditions, whereas the stability of PMMA is not significantly influenced by the storage condition. Protein adsorption studies were carried out and showed that there is a significant reduction in the amount of protein adsorption on UVO-treated plastics compared with untreated plastics. Lastly, UVO-treated PMMA microchannels were fabricated and used for capillary-driven flow, which revealed that longer treatment durations generate faster flow rates. These collective results offer new insights into the utility of UVO-treated plastics for microfluidic analytical applications.