Nanosilver is widely used in consumer products thanks to its antimicrobial properties. However, such widespread use means that other microorganisms, aside target bacteria and fungi, would be exposed to these particles too. Micoorganisms in surface water ecosystems and wastewater treatment plant microbial communities could be particularly exposed, as could humans.

Living organisms all have something in common – they contain enzymes (proteins that catalyze complex and specific biochemical reactions at high speeds and at ambient or body temperatures) in their cells. To study the impact of silver nanoparticles (AgNPs) on enzymes we chose firefly luciferase as a model since this enzyme’s activity can easily be measured by recording its light output.

We have found that 20 nm citrate-coated AgNPs inhibit the activity of this enzyme, and that the extent of inhibition depends on the nanoparticle dose. We examined the mechanism behind this effect by characterizing the physicochemical properties of the enzyme and how it biophysically interacted with the AgNPs. We also quantified the amount of silver ions released from the AgNPs during this interaction.

We discovered that mixing the enzyme and AgNPs triggered a red shift of 44 nm in the light absorbance peak of the AgNPs. This produced a so-called luciferase protein corona that was 20 nm thick on the nanoparticle surfaces (figure 1). However, we also found that the secondary structures of the luciferase were only marginally affected upon formation of this corona, something that we verified using circular dichroism spectroscopy and multiscale discrete molecular dynamics simulations.

By comparing the enzymatic inhibitory patterns of AgNPs and Ag-ions we showed that the inhibition was primarily due to silver ions being released from AgNPs. We believe that the fact that silver ions have a high affinity towards Cys residues and nitrogen groups on the enzymes may be the main cause behind the inhibition.

More information can be found in the journal Nanotechnology 24 345101

Further reading

Magnetic nanoparticles move cells to target (Jan 2008)
New insight into the biocide behaviour of nano silver (Apr 2011)
Antibacterial coatings: taking lessons from nature (Dec 2012)
Interaction of multifunctional silver nanoparticles with living cells (May 2010)