Nanoparticles with controllable toxicity provide an antimicrobial strategy with a small environmental footprint

Swiss scientists have developed an antimicrobial strategy using lanthanum oxide nanoparticles to compete against microbes for phosphate. The availability of phosphate, an essential component of nucleic acids, proteins and cellular energy carriers, is often the limiting factor in microbial growth in aqueous environments. 

Lanthanum is a rare earth metal known to have a high affinity for phosphate, a property which has seen the use of lanthanum carbonate (trade name Fosrenol) as a phosphate binder prescribed to patients with kidney disease to reduce the excess levels of phosphate in their blood. When bound to phosphate, a stable, non-toxic complex is formed. Robert Grass, who led the team at the Swiss Federal Institute of Technology, Zurich, says that the lanthanum nanoparticles show particular promise in water treatment, where he aims to achieve completely phosphate-free water to drastically limit the growth of microbes.


Scanning electron microscopy images of (a) lanthanum oxide nanoparticles and (b) lanthanum oxide nanoparticles exposed to a phosphate containing solution, resulting in the formation of small spikes

However, concerns have already been raised over the increasing use of rare earth metals and their toxicity in the environment. During their investigations, the team found that they could detoxify the nanoparticles by using excess phosphate as an external switch. Grass explains that ’rather than taking lanthanum out of the system, which would be a very difficult procedure, we can add phosphate and turn off the toxicity’. This provides an antimicrobial solution with the potential to bypass toxic material release and is shown to be highly effective against bacterial, fungal and algal species.

Young-Shin Jun, who heads the environmental nanochemistry laboratory at Washington University in St. Louis, US, says that the study ’provides valuable insight into the fate of rare earth oxides in water treatment plants and the oxides’ potential impacts on microbes in the plants’. She adds that this strategy may be extended to other rare earth oxides. 

The challenge now facing Grass’s team is how to recycle their nanoparticles for future use. As the phosphate complex is so stable, very harsh chemical conditions are required to regenerate lanthanum oxide. ’If we go into water treatment, we will certainly have to think about how we can reuse the material,’ says Grass.

Michael Parkin