Carmen Say

Publication Date


Document Type

Honors Thesis




Biofilms-Surfaces, Biofilms-Growth, Surface chemistry, Nanoscience, Nanoscale, Topography


The field of nanotechnology is growing rapidly. Progress in this field depends in part on a thorough understanding of surface properties, and on the physical and biological consequences of such properties. Our previous work on the aqueous chemistry of hydrogen-terminated silicon demonstrated that deoxygenated H2O etching produces surfaces with highly-ordered nanoscale features. We have also examined the adsorption of biomolecules to silica-based surfaces by using poly-L-lysine (PLL) and alginate to serve mimics of early biofilm stages: surface chemistry plays a major role in the nucleation stage of growth and affects the resulting film morphology. These seemingly disparate projects come together in our current exploration of the effects of surface chemistry and nanotopography on biofilm colonization and growth. Here, we examine the influence of substrate hydrophobicity and nanoscale topography on the biofilm development of Pseudomonas aeruginosa NIH3/pMQ80-82, a strain that has GFP under the control of an inducible arabinose promoter. We propose that biofilm formation will be enhanced by the surface chemistry and nanoscale structuring of our etched Si-based substrates, and that the architecture and thickness of the films will differ because of the independent or joint effects of these properties. Visual analysis with fluorescence and laser scanning confocal microscopy showed that the biofilms formed on rough hydrophobic substrates after 4 days of incubation at 37 ºC were large and dense; on rough hydrophilic substrates were small and dense; and on flat hydrophobic substrates were extensive but not dense. No biofilm formation was seen on the flat hydrophilic substrate (control) under the same growth conditions. The uniformity in thickness of the biofilms on the flat hydrophobic surface was greater than that of the biofilms on the rough hydrophobic surface, as revealed by LSCM image analysis of the topography of the biofilms. viii The results from the E.coli and the biofilm mimic experiments also supported the finding that the rough hydrophobic substrate most significantly influences bacterial adhesion. Contact angle measurements of the PLL and alginate adsorption showed that the films on the rough hydrophobic substrate were more homogeneous than those on the flat hydrophobic substrate. This was seen by the relatively small hysteresis (max 7°) for the films on the rough hydrophobic surface compared to the very large hysteresis (>50°) for the films adsorbed on the flat hydrophobic surface. Taken together, the results of this study are consistent with what is reported in literature about the enhancing effects of nanoscale surface topography and hydrophobicity on bacterial adhesion. However, more quantitative data using image analysis of fluorescence and LSCM images can provide a more complete understanding of the specific effects surface chemistry and nanotopography have on biofilm development




viii, 86 p. : ill. (chielfly col.) Honors project-Smith College, Northampton, Mass., 2011. Includes bibliographical references (p. 84-86)