WORK PACKAGE 2: THE IMPORTANCE OF THE NANOMATERIAL SURFACE

Coating of particles is critical when it comes to their toxicity. That is why it is interesting to investigate the formation of a primary corona of environmental organic material on nanoparticles. More specifically, how that corona influences interactions between nanoparticles, organisms and biomolecules.

Results so far: Silica nanoparticles do not aggregate in solutions of natural organic matter (NOM). This was unexpected, and is an important clue to the fate of these particles, as aggregation is a necessary first step towards sedimentation. The high stability of these particles suggest that they could spread from a point source over quite a large area. But on the other hand they are likely to be diluted by this transport, which make them less toxic.

Nanoparticles released into nature may have an impact on the ecosystem on several different levels. Therefore, it is important to know how and where the nanoparticles interact with organisms. The surface of nanoparticles will likely be changed when the particles are released into nature, as biomolecules will bind to them. This biomolecular corona has been shown to be important for how nanoparticles interact with cells, and it is likely that it will also influence the nanoparticles’ interaction with organisms.

Jörgen Rosenqvist, University of Gothenburg Dept of Chemistry and Molecular Biology

Nanoparticles behaviour

To understand how nanoparticles behave, if they are released into natural waters, either by design or by accident, it is necessary to know how the particles behave when they come into contact with other substances in the water, such as different organic and biological molecules. Caroline Jonsson, assistant professor, and Jörgen Rosenqvist, researcher, at the Department of Chemistry & Molecular Biology at the University of Gothenburg have been studying the interactions. Natural organic molecules of various sizes naturally found in runoff waters, streams and lakes interact with silica nanoparticles differently depending on their size and surface charge, as well as the pH and salt concentration of the molecular suspensions.

The nanoparticles are affected by organic molecules

They have found that the structure of the biological corona is affected by the nature of the organic molecules and by the size and charge of the nanoparticles. For example, the presence of the small molecule dihydroxybenzoic acid (DHBA) significantly affects the surface charge of silica nanoparticles at environmentally relevant pH values. Jörgen Rosenqvist argues that natural organic matter (NOM) are the most important type of molecules in natural waters:

“The interaction between these molecules and the nanoparticles will largely decide the fate of the particles” says Jörgen Rosenqvist. “I feel a strong need to understand the potential hazards associated with this. Hopefully, through this research, we can eliminate some particles from the “potentially hazardous” list and develop some new screening protocols.”

"To develop a fate model for silica nanoparticles by adopting multi-scale modeling approach, we started by performing simulation on molecular level. Molecular dynamics simulations allow us to observe interaction between simple organic molecules and silica surface", says Krzysztof Kolman, PhD student University of Gotheburg, Dept of Chemistry and Molecular Biology.

 

Exchanging results with other groups

A theoretical model that describes the surface charging of silica nanoparticles of various sizes at different pH as well as in different salt solutions has been developed by Associate Professor Zareen Abbas, also at the Department of Chemistry & Molecular Biology at the University of Gothenburg. The predictions from this theory are that the surface charge of silica nanoparticles in a salt solution increases as the particle size decreases. The aim is now to compare the calculated surface charge densities with the corresponding experimental data obtained by Jörgen and Caroline.

Input to regulatory authorities

In the long run, Jörgen also aims to give input to the regulatory agencies regarding which types of particles should be regulated and which do not need regulation. The use of new types of industrial products containing nanoparticles is increasing rapidly and it is crucial to quickly find out if there are any hazards that the product developers haven’t thought of yet.

“To completely understand the fate and potential hazards of a certain kind of nanoparticles, we need to understand how the particles interact with water, organic molecules, mineral surfaces, and living organisms of many different kinds,” says Jörgen Rosenqvist. “It is sometimes quite difficult to determine which paths are important for the big picture and which paths are possible, but so improbable, that they’re not of any real importance [to study].”

Tommy Cedervall, University of Lund, Dept of Biochemistry and Structural Biology

 

How biomolecules influence the nanoparticles

At Lund University, Tommy Cedervall’s research team investigates how biomolecules, including proteins from the zooplankton Daphnia magna that are bound to the nanoparticle surface, influence the dispersion of nanoparticles in water and the binding of other proteins to the surface. One of the main challenges is to identify what properties of a nanoparticle in general that may be dangerous for the environment. The MISTRA Environmental Nanosafety program can contribute important knowledge about how nanoparticles with different shape, size and surface chemical properties are modified by natural biological molecules, and how the modified particle, as compared to bare particles, affect aquatic organisms and ecosystems, explains Tommy Cedervall.

“The use and production of nanoparticles is increasing and, as a result, the release of nanoparticles into nature will simultaneously increase. The potential risks of nanoparticles in nature are not yet known, and although I do not believe that nanoparticles in general will be a larger problem than the bulk material, I think there is a high probability that some nanoparticles are. Therefore there is a need for extended ecotoxicological studies”, says Tommy Cedervall.

New method to study nanoparticles adsorption

In order to understand how, and eventually to control, biomolecular binding to nanoparticle surfaces, a new method to study the real time interaction of proteins to silica nanoparticle surfaces has been created by Rickard Frost, Post doc researcher at the Department of Physics, Chalmers, under the direction of Associate Professor Christoph Langhammer.

"My entire research activities are focusing on nanoparticles and how they can be useful for us. It thus is natural and very important to also ask the question if and when they might be harmful.", says Christoph Langhammer.

The Chalmers research group has developed a new version of a nanoplasmonic sensor. It utilizes spheroidal gold nanoparticles covered by a thin layer of silica, to form a core-shell structure with built-in sensing function. Upon illumination with white light, the plasmon resonance in the gold core is excited. Adsorption of molecules to the silica shell will change the plasmon resonance, a change that can be continuously measured. In this manner, adsorption events on the nanoparticle’s silica surface can be detected in situ and in real time. The new sensor has been used to study the adsorption behavior of proteins of interest from Tommy Cedervall’s lab onto the silica nanoparticles.

Low environmental risks of dispersion of tungsten carbide

Professor Inger Odnevall Wallinder’s research team at the Division of Surface and Corrosion Science, KTH Royal Institute of Technology, focuses on metallic nanoparticle environmental transformation, dissolution, interaction, fate and release of ionic species in contact with aquatic settings of different chemistry and redox conditions. Their research contributes with knowledge on the fate of metal nanoparticles in the environment and whether they are in a toxic form or not. Knowledge on effects of biomolecule adsorption to metallic nanoparticles and chemical speciation knowledge enables the prediction of particle reactivity and hazards towards aquatic organisms. In order to investigate the potential hazard from WC particles mixed with Co, the KTH team, with Dr Jonas Hedberg as the driving researcher, has analyzed WC and WC-Co nanoparticles in the laboratory under realistic conditions observed in the environment adjacent to traffic areas.

"There is a high scientific value in examining the metals that are highly reactive, because there are not so much data to be found about them", says Inger Odnevall Wallinder.

The smallest particles the most stable

They have found that interaction between the WC particles and biomolecules of natural organic matter is very sparse, and this results in rapid agglomeration and sedimentation of the particles, and hence limited transport and mobility in aquatic systems. However, the smallest fraction of WC nanoparticles was more stable in solution and sedimented at a slower rate compared with the larger fraction. These nanoparticles are therefore more prone to be mobile and transported into different aquatic settings of the environment and should be considered in future studies. Parallel studies with WC-Co nanoparticles show that almost all Co was released from the nanoparticles within 24 hours. These aspects need to be considered from an environmental perspective, as soluble species of Co may, under some circumstances, be toxic.

“An improved understanding of the environmental fate of dispersed metal nanoparticles is essential for risk assessment and risk management of their use in different applications”, says Inger Odnevall Wallinder. “ We want to contribute with knowledge to prevent and mitigate risks of nanoparticles dispersions at an early stage of usage to minimize potential negative environmental effects”.

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