Antimicrobial and bacteria-releasing multifunctional surfaces: Oligo (p-phenylene-ethynylene)/poly (N-isopropylacrylamide) films deposited by RIR-MAPLE

Antimicrobial oligo (p-phenylene-ethynylene) (OPE) films have previously been demonstrated to show effective ultraviolet A (UVA) light-induced biocidal activity; however, a serious problem arises from the accumulation of dead bacteria and debris on the films that limits their effectiveness and application. In this work, we address this challenge by incorporating thermally-responsive poly (N-isopropylacrylamide) (PNIPAAm), which provides on-demand bacteria-releasing functionality. Multifunctional surfaces comprising blended films of OPE and PNIPAAm were deposited on substrates by resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) using a sequential co-deposition mode. In this way, RIR-MAPLE enabled the deposition of multifunctional films with surface properties and film functionality that can be tailored, precisely and systematically, by controlling the chemical composition of the deposited film. The surface properties of these films were characterized by UV-visible (UV-vis) absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurements. The interactions between bacteria and the deposited films were tested using two model bacteria: Escherichia coli K12 (Gram-negative) and Staphylococcus epidermidis (Gram-positive). The antimicrobial and bacteria-release properties of the blended films were controlled by varying the OPE/PNIPAAm ratio in the RIR-MAPLE emulsion target, providing an easy way to optimize the multifunctional surface. The OPE/PNIPAAm blended films with optimized composition killed a majority of attached E. coli bacteria at 37 °C and under UVA exposure, and the dead bacteria were then removed from the films simply by rinsing with water at 25 °C.