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We investigated the effect of two brush parameters, thickness and dispersity in the molecular weight distribution, on the adhesion of bacteria to pH-responsive poly(acrylic acid) (PAA) brushes synthesized using surface-initiated atom transfer radical polymerization. The attachment and detachment of Staphylococcus epidermidisto PAA brushes at pH 4 and pH 9, respectively, were examined with confocal microscopy. An optimal range of brush thickness, 13–18 nm, was identified for minimizing bacterial adhesion on PAA brushes at pH 4, and bacterial attachment did not depend on the brush dispersity. Increasing either the brush thickness or dispersity detached bacteria from the brushes when the pH was increased from 4 to 9. Bacterial detachment likely arose from an enhanced actuation effect in thick or high-dispersity brushes, as PAA brushes change conformation from collapsed to extended states when the pH is increased from 4 to 9. These results suggest that manipulating the molecular weight distribution provides a route to separately tune the attachment and detachment of bacteria.

We investigate the effect of interfacial properties on the adhesion of bacteria at oil/water interfaces using confocal microscopy. Surfactant-decorated dodecane droplets of diameter 20–60 μm are generated using a coflow microfluidic device, introduced into an aqueous saline suspension of Marinobacter hydrocarbonoclasticusbacteria, and imaged in 3-D over time. Using image analysis algorithms, we determine the number of bacteria adhering at oil/water interfaces over time in the presence of dioctyl sodium succinate (DOSS), a component of the dispersant used in oil-spill recovery. The adsorption of bacteria at the oil/water interface follows Langmuir first-order kinetics for all droplet sizes, with the greatest areal number density of bacteria adhered to the smallest droplets. We vary the surfactant type [DOSS, dicyclohexyl sodium sulfosuccinate, dibutyl sodium sulfosuccinate, cetyltrimethylammonium bromide, and Tween 20] and concentration and examine the effects on long-time adhesion of bacteria. For a fixed droplet size, the areal density of bacteria at the interface decreases with increasing surfactant concentration because of a reduction in oil/water interfacial tension that increases the free energy of adhesion of the bacterium.