Entropic repulsion caused by interfacial orientational fluctuations of cholesterol layers restricts protein adsorption and bacterial adhesion, providing a conceptually new physicochemical perspective on biointerfaces that may guide future material design in regulation of adhesion.
Materials All chemicals (solvents, lipids, media, proteins and so on) used in this article were purchased from Sigma-Aldrich without further purification, except where stated otherwise. Lipid layer preparation SCLs SCLs were prepared on silicon wafers (10 × 15 mm2). The substrates were cleaned by immersion in a solution of deionized water, ammonia and hydrogen peroxide (volume fraction 5/1/1) for 15 min at 70 °C, rinsed repeatedly in Milli-Q water and then dried in a nitrogen stream. The cleaned substrates were immediately used for the preparation of SCLs by spin-coating. Compounds were dissolved in chloroform at a concentration of 2 wt% (unless stated otherwise), and spin-coating (LabSpin6, SÜSS MicroTec) was performed at 3,000 rpm s–1 for 30 s. SAMs Silicon wafers were cleaned as described for SCL preparation. Clean substrates were first coated with a 3 nm chromium adhesion layer and then a 50 nm gold layer by chemical vapour deposition performed at 5 × 10–5 mbar (Univex 300, Leybold). Gold substrates were cleaned by immersion in a solution of deionized water, ammonia and hydrogen peroxide (volume fraction 5/1/1) for 15 min at 70 °C, rinsed repeatedly in Milli-Q water and then dried in a nitrogen stream. To minimize defects, the gold substrates were used for SAM formation immediately after cleaning. Thiol compounds were dissolved in ethanol (analytically pure, p.a.) to a concentration of 1 mM. Before use, thiol solutions were sonicated for 5–10 min. Gold-coated substrates were additionally cleaned in ethanol (p.a.) for 30 min using an ultrasonic bath. Subsequently, samples were immersed in thiol solutions and incubated for 24 h to ensure complete assembly. Containers housing the solution and samples were filled with dry nitrogen and sealed to minimize oxygen exposure. After incubation, sample surfaces were rinsed for 15–20 s with ethanol (p.a.), dried under nitrogen and used directly for further experiments. Preparation of thiocholenic acid For the…
Friedrichs, Institute Of Biofunctional Polymer Materials, Leibniz Institute Of Polymer Research Dresden, Dresden, Helbig, Hilsenbeck, Pandey, Prithvi Raj, Institute Of Theory Of Polymers, Sommer