BioNanoAdhesion

The objective of this research was to investigate nanoscale adhesion in a number of scientifically interesting systems. To do this, self-assembled monolayers (SAMs) of alkanethiols and dialkyl disulfides have been formed on thermally evaporated gold films, presenting a variety of chemically modified surfaces. Adhesion studies involving atomic force microscopy (AFM), nanoparticles and living cells have been performed employing the SAMs. The wetting behaviour, elemental composition, thickness and surface topography of the SAMs were assessed. Only one of the SAM compounds was found to have not formed a SAM successfully. The compound contained a terminal quaternary pyridinium moiety, and it is believed the SAM formation was unsuccessful due to interaction between the iodide counterion and the gold surface. The contact angle titration behaviour of the SAMs was investigated over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. It was found that both pH and electrolyte concentration had little or no effect on the contact angle titration behaviour of the SAMs. The effect of pH on the adhesion of poly(styrene) nanoparticles presenting a range COOH and NH2 surface chemistries was studied, using SAMs presenting CH3, COOH, OH, and pyridine moieties. Adhesion was generally found to decrease with increasing pH due to increased repulsive forces between surfaces. A range of surface morphologies for the adsorbed nanoparticles was observed. AFM adhesion measurements were performed in aqueous electrolyte solutions over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. Adhesion was found to vary with both pH and electrolyte concentration, with the wetting behaviour of the surfaces, surface charge and contact area between surfaces affecting the measured forces. Finally, the settlement and adhesion of zoospores of the green alga Ulva linza and the diatom Navicula perminuta to eight of the SAMs, with SAM surface chemistry and SAM alkyl chain length the system variables. Adhesion was influenced by the surface chemistry and wetting behaviour of the SAMs. The adhesion of both organisms to methyl-terminated SAMs was found to decrease with increasing SAM alkyl chain length, which was attributed to changes in the phase state and tribology of the SAMs. The adhesion of Navicula perminuta to SAMs was also affected by the surface chemistry of the SAM