Environmental Science: Nano Blog

Virtually all environmental surfaces have microbial biofilms, which are an essential component of natural systems.  Nanoparticles are abundant in nature, but how much do we know about nanoparticle-biofilm interactions?

Kaoru Ikuma and colleagues from the University of Massachusetts Amherst have completed a study highlighting the importance of assessing small-scale biofilm surface characteristics in future nanoparticle-biofilm interaction studies. They hypothesized that the contribution of electrostatic forces in relation to other forces would be dominant in governing the deposition of bare nanoparticles onto polysaccharide-coated surfaces. The also expected biofilm surface charge to impact nanoparticle deposition.

Polysaccharides are a major extracellular component of biofilms. They are ubiquitous in the environment and occur in pure forms as well as in complexes. As polysaccharides are extracellular they are an initial point of contact for nanoparticles and play an important role in early nanoparticle-biofilm interactions. Typical characterization of biofilms often treat all polysaccharides as one entity.  This study suggests that the small-scale chemical and electrochemical identities of the polysaccharides present in the biofilms may play an important role in the initial surface attachment of nanoparticles; therefore effecting their deposition.

The significance of polysaccharide coatings on the deposition of nanoparticles was examined using in-depth characterization of surface properties. It would appear that surface charge density and distribution of the biofilms both contribute to different nanoparticle deposition behaviours.

Kelvin probe force microscopy was used as a probe for spatial variations of surface potential across two different polysaccharides (alginate and dextran sulphate). Patches of lower surface potential are observed as the areas of darker colour on the images below.

alginate (a) and dextran sulfate (b)

The results showed that even though the interactions between nanoparticles and surfaces coated with pure polysaccharides may be governed by electrostatic forces, these interactions can be altered by microscale and nanoscale differences in surface charge. Therefore, instead of treating polysaccharides as one entity, spatial characterization of biofilm surface properties is necessary to improve our understanding of nanoparticle-biofilm interactions.

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Deposition of nanoparticles onto polysaccharide-coated surfaces: Implications for nanoparticle-biofilm interactions. Kaoru Ikuma, Andrew Madden, Alan Decho and Boris L. T. Lau 10.1039/C3EN00075C

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One of our recent Environmental Science: Nano papers looks into the effect of natural organic matter on the disagglomeration of manufactured TiO₂ nanoparticles.

This research, conducted by Frédéric Loosli and colleagues from the University of Geneva, studied the stability of TiO₂ nanoparticles at various pH values.

TiO₂ nanoparticles (the most produced nanoparticles to date) are used in consumer goods such as cosmetics, paints and as a UV protection agent. These consumer goods are then released into our environment, but there is a lack of data on nanomaterial transformations under relevant environmental conditions.

It is generally assumed that agglomerated nanoparticles are less toxic to aquatic organisms than single nanoparticles. As a given amount of nanoparticles will enter aquatic environments in an agglomerated, potentially less toxic form, the potential risk comes from natural processes which may considerably alter the stability of such agglomerated nanoparticles. Such processes have the possibility to disperse them, increasing diffusion and potential toxicity of the nanoparticles.

This study looked at the effects of two types of natural organic matter, at typical environmental concentrations, to determine if their presence induced significant disagglomeration of large submicron nanoparticle agglomerates. The natural organic matter used for this research were: Suwannee River humic acid, which can act as a pH regulator, and Alginate, which is found in the cell walls of seaweed and is commonly used in the food industry as a stabilizer and a thickening agent.

Figure 1

It was shown that the addition of natural organic material significantly modifies the stability of TiO₂ nanoparticles by inducing disagglomeration. Figure 1, taken from the paper, demonstrates how alginate and Suwannee River humic acid effect the disagglomeration of agglomerated nanoparticles differently.

To find out more about this research, download your free* copy by following the link below:

Effect of natural organic matter on the disagglomeration of manufactured TiO₂ nanoparticles by Frédéric Loosli, Philippe Le Coustumer and Serge Stoll DOI: 10.1039/C3EN00061C

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