Superhydrophobic and superhydrophilic nanocomposite coatings for preventing Escherichia coli K-12 adhesion on food contact surface

Many recent studies have shown that both superhydrophobic and superhydrophilic coatings potentially minimize microbial adhesion to solid substrates; however, a comprehensive investigation of both extreme surface characteristics is not available to date. Therefore, this study was aimed to test and compare the amounts of bacteria adhered to superhydrophobic and superhydrophilic nanocomposite surfaces under different fluid flow conditions. The superhydrophobic and superhydrophilic layers were separately fabricated by annealing stainless steel plates with carbon nanotubes-polytetrafluoroethylene (CNT–PTFE) and titanium dioxide (TiO2), respectively. The phosphate buffer saline (PBS) suspension of Escherichia coli K-12 at 3 × 108 cells/ml was pumped through the chamber at two different flow rates of 0 (stagnant surface) and 200 ml/min (sheared surface). Field emission scanning electron microscope (FESEM) and atomic force microscope (AFM) were used to access the morphologies of the developed nanocomposite surfaces. Fluorescence intensities (FIs) of bacteria adhered to superhydrophobic and superhydrophilic surfaces were up to approximately 80% and 65% lower than uncoated surface when wall shear rates were 37 (sheared surface) and 0 s−1 (stagnant surface), respectively. The bacterial reduction on the surface of parallel plate unit (i.e., duct) would promisingly decrease the risk of cross-contamination between liquid food and biofilms which may cause serious problems in ready-to-eat food produces. Coated surfaces are expected to require lower amounts of water and chemicals used for cleaning-in-place (CIP) program.