Comparison of Types and Amounts of Nanoscale Heterogeneity on Bacteria Retention

Abstract

Interaction energy calculations that assume smooth and chemically homogeneous surfaces are commonly conducted to explain bacteria retention on solid surfaces, but experiments frequently exhibit signification deviations from these predictions. A potential explanation for these inconsistencies is the ubiquitous presence of nanoscale roughness (NR) and chemical heterogeneity (CH) arising from spatial variability in charge (CH1), Hamaker constant (CH2), and contact angles (CH3) on these surfaces. We present a method to determine the mean interaction energy between a colloid and a solid-water-interface (SWI) when both surfaces contained binary NR and CH. This approach accounts for double layer, van der Waals, Lewis acid-base, and Born interactions. We investigate the influence of NR and CH parameters and solution ionic strength (IS) on interaction energy profiles between hydrophilic and hydrophobic bacteria and the SWI. Increases in CH1 and CH3 reduce the energy barrier and create deeper primary minima on net electrostatically unfavorable surfaces, whereas increasing CH2 diminishes the contribution of the van der Waals interaction in comparison to quartz and makes a more repulsive surface. However, these roles of CH are always greatest on smooth surfaces with larger fractions of CH. In general, increasing CH1 and CH3 have a larger influence on bacteria retention under lower IS conditions, whereas the influence of increasing CH2 is more apparent under higher IS conditions. However, interaction energy profiles are mainly dominated by small fractions of NR, which dramatically lower the energy barrier height and the depths of both the secondary and primary minima. This significantly increases the relative importance of primary to secondary minima interactions on net electrostatically unfavorable surfaces, especially for conditions that produce small energy barriers on smooth surfaces. Energy balance calculations indicate that this primary minimum is sometimes susceptible to diffusive removal depending on the NR and CH parameters.

Evidence for the critical role of nanoscale surface roughness on the retention and release of silver nanoparticles in porous media

“…Furthermore, differences in AgNP retention on QW and GF sands are not predicted because values of F max were nearly identical (39.4 and 40.1 for QW and GF sand, respectively). Potential explanations for these discrepancies include nanoscale charge heterogeneity and roughness which can locally reduce and/or eliminate the energy barrier (Suresh and Walz, 1996;Bhattacharjee et al, 1998;Hoek et al, 2003;Hoek and Agarwal, 2006;Bradford et al, 2017;Bradford et al, 2018). Nanoscale chemical heterogeneity that is larger than a critical size can create regions on a net unfavorable surface that are favorable for interaction between the colloid and the solid surface due to a local reduction in the energy barrier and an increase in the depth of the primary minimum.…”

Transport and retention of engineered silver nanoparticles in carbonate-rich sediments in the presence and absence of soil organic matter

“…SOM has been found to mask charge heterogeneities and cation bridging with clay particles (Cabal et al, 2010;Han et al, 2008). The interaction of SOM with AgNPs is also expected to be sensitive to the roughness density and height of the AgNP capping agent (Bradford et al, 2017(Bradford et al, , 2018 and the bonding energy between the capping agent and the AgNP (Gunsolus et al, 2015). Additional research is warranted to determine the underlying cause for differences in SOM-AgNP interactions, but a systematic evaluation of these factors is beyond the scope of this work.…”

“…However, no research has systematically examined the influence of calcite with impurities from silicate minerals and/or SOM coatings on AgNP transport. Chemical heterogeneities (CH) in such media will produce variations in charge, Hamaker constant (Bradford et al, 2018), and/or hydrophobicity (Tschapek, 1984).…”

“…The collector surface roughness has been found to play an important role in controlling the mobility and fate of nanoparticles due to its strong influence on interaction energies, hydrodynamic forces, and lever arms associated with hydrodynamic and adhesive torques (Morales et al, 2009;Torkzaban et al, 2010). When small amounts of NR occur on both porous medium and colloid surfaces the magnitudes of the secondary and primary minima, and the energy barriers are all strongly reduced in comparison to a smooth surface (Bendersky and Davis, 2011;Bhattacharjee et al, 1998;Bradford et al, 2018;Bradford and Torkzaban, 2013;Hoek and Agarwal, 2006), and the colloid may be susceptible to diffusive and/or hydrodynamic removal (Bradford and Torkzaban, 2015;Rasmuson et al, 2017). These changes in the interaction energy profile may even occur in the presence of CH, such that electrostatically favorable locations are unfavorable for colloid retention (Zhang et al, 2016).…”

A Sticking Point in Assessing Bacterial Contamination: Adhesive Characters of Bacterial Specializations, Swab Features, and Fomite Surface Properties Skew Colony Counts

“…It has been shown that the intrinsic surface properties of different types of plastics affect both long and short term bacterial adhesion to their surfaces (Cai et al, 2019). Variations in roughness on a nanoscale and surface chemical heterogeneity further confound assessment of bacterial adhesion onto fomites (Bradford et al, 2018).…”