Scientists at Cardiff University have developed an innovative imaging method that facilitates pollution monitoring based on the accurate detection of gold nanoparticles in woodlice. The approach provides details on the quantity, location and impact of gold nanoparticles to improve our understanding of their toxicity and the potential harm other metals may have on the environment.
With gold nanoparticles being increasingly employed in medical devices, biological research and industry due to their biocompatibility and photostability, it is important to investigate the effect they can have when leaching out into nature. As woodlice can be found in heavily metal-contaminated areas because of their specialized digestive organ, known as the hepatopancreas, which stores and expels unwanted metals, this offers an opportunity to assess how gold nanoparticles behave in complex biological systems and on nearby organisms.
The detection of metal nanoparticles, and especially gold, requires microscopic 3D imaging, which cannot be carried out in the field. As reported in Applied Physics Letters [Pope et al. Appl. Phys. Lett. (2023) DOI: 10.1063/5.0140651], here the team devised an imaging method called four-wave mixing (FWM) microscopy that allows gold nanoparticles to be imaged background-free inside highly scattering environments and multicellular organs. It uses flashing light that the gold nanoparticles then absorb – when the light flashes again, the subsequent scattering shows the position of individual nanoparticles in a 3D cellular environment.
The technique was demonstrated to detect individual gold nanoparticles with a radius as small as 5nm in background free, with high contrast and high 3D location precision inside multicellular organs. As author Wolfgang Langbein stated, “By precisely pinpointing the fate of individual gold nanoparticles in the hepatopancreas of woodlice, we can gain a better understanding of how these organisms sequester and respond to metals ingested from the environment.”
In turn, this will show if gold accumulates in particular cells or whether it interferes with the metabolisms in high doses.Also, as the approach is specific to gold nanoparticles, it can distinguish it from other metals, as well as organisms such as fish larvae and even human cell cultures.
The team now hope to develop the FWM approach to allow fast single gold nanoparticle tracking, with the idea of following the transport of gold nanoparticles across biological barriers, such as in model systems of the blood–brain-barrier, and to achieve better insight and understanding for drug delivery. They also plan to use single gold nanoparticlesas a tag to track viral particles with the aim of better understanding their intracellular journey and in turn their infection mechanism.
“By precisely pinpointing the fate of individual gold nanoparticles in[...] woodlice, we can gain a better understanding of how these organisms sequester and respond to metals ingested from the environment.”Wolfgang Langbein
(a) Cartoon of a woodlouse depicting the hepatopancreas (HP) and the hind gut (HG); (b) transmission overview of a single HP tubule, showing the helical structure; (c) section from a HP tubule with the nuclei fluorescently labelled in blue. Cells are attributed as type B, identifiable by their double nucleus and larger shape (indicated by white arrows), and to type S identifiable by their single nucleus and smaller shape (indicated by black arrows). The dashed box indicates the region imaged by FWM; (d) reflection image acquired simultaneously with the FWM image. Cell boundaries have been inferred from the contrast in the image and marked with dashed white lines; (e) false color FWM image, gold nanoparticles appear red while other metal deposits appear yellow. The dashed white lines are the same as the reflection image and are added as an aid to the eye; (f) and (g) are zooms of the regions indicated by the colored dashed boxes in (e).