Molecular Adhesion of a Pilus-Derived Peptide Involved in Pseudomonas aeruginosa Biofilm Formation on Non-Polar ZnO-Surfaces.

Bacterial colonization and biofilm formation on abiotic surfaces are initiated by the adhesion of peptides and proteins. Understanding the adhesion of such peptides and proteins at a molecular level thus represents an important step toward controlling and suppressing biofilm formation on technological and medical materials. This study investigates the molecular adhesion of a pilus-derived peptide that facilitates biofilm formation of Pseudomonas aeruginosa, a multidrug-resistant opportunistic pathogen frequently encountered in healthcare settings. Single-molecule force spectroscopy (SMFS) was performed on chemically etched ZnO 11 2 ‾ 0 ${\left(11\bar{2}0\right)}$ surfaces to gather insights about peptide adsorption force and its kinetics. Metal-free click chemistry for the fabrication of peptide-terminated SMFS cantilevers was performed on amine-terminated gold cantilevers and verified by X-ray photoelectron spectroscopy (XPS) and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Atomic force microscopy (AFM) and XPS analyses reveal stable topographies and surface chemistries of the substrates that are not affected by SMFS. Rupture events described by the worm-like chain model (WLC) up to 600 pN were detected for the non-polar ZnO surfaces. The dissociation barrier energy at zero force ΔG(0), the transition state distance xb and bound-unbound dissociation rate at zero force koff (0) for the single crystalline substrate indicate that coordination and hydrogen bonds dominate the peptide/surface interaction.

Combined in-situ attenuated total reflection-Fourier transform infrared spectroscopy and single molecule force studies of poly(acrylic acid) at electrolyte/oxide interfaces at acidic pH.

Fundamental adsorption mechanisms of poly(acrylic acid) (PAA) electrolyte/oxide interfaces were analyzed by the combination of in-situ attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and single molecule force spectroscopy (SMFS). The approach aims at a fundamental understanding of initial states of polymer fouling in chemical microreactors. While the presented FTIR-data provide information on adsorption and desorption kinetics, SMFS studies reveal the corresponding interfacial and intermolecular forces. Silicon oxide and oxide covered FeCr alloy films with small concentrations of Ni were chosen as reference systems for relevant technical reactor components. Adsorption and desorption studies were performed in aqueous electrolytes at acidic pH to simulate the polymerisation process. Ex-situ ellipsometry and atomic force microscopy (AFM) studies of the adsorbed polymer layers as well as X-ray photoelectron spectroscopy (XPS) of the oxide surfaces complemented the analytical approach. The comparison of the in-situ ATR spectroscopic results and the SMFS data revealed higher molecular adhesion forces on FeCr-oxide covered FeCr alloy films in comparison to the SiOx terminated surfaces. The different interactions could be assigned to the specific coordination bonds formed between the carboxylic acid group and surface metal ions in the case of FeCr alloy films. AFM images showed related changes in interfacial film formation.

Single-Molecule Desorption Studies of Poly(acrylic acid) at Electrolyte/Oxide/TiAlN Interfaces.

The presented studies correlate the surface chemistry of electrochemically oxidized TiAlN hard coatings with the desorption forces of poly(acrylic acid) (PAA) at the electrolyte/oxide/TiAlN interface. Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) was performed at different pH values to investigate surface chemistry-induced changes in desorption force. The chemical state was characterized by X-ray photoemission spectroscopy and electrochemical analysis. The results show that the desorption forces continuously decrease with increasing pH in the range from pH 5 to 9. The comparison of the desorption forces on rf-sputtered titanium dioxide and aluminum oxide films shows that the electrochemically oxidized surface of TiAlN, in agreement with the revealed surface composition, shows interfacial adhesive properties in contact with PAA and water that resemble a pure titanium oxide layer. Load rate-dependent measurements were performed to analyze both the free energy barrier and the transition state distance.