Nanoscale chemical imaging and spectro-microscopy of engineered nanomaterials after interaction with aquatic environmental media and microorganisms

Session

Poster Session 2

Authors

Dr. Miguel Gomez-Gonzalez (2), Mr. Yunyang Wang (3), Dr. Fang Xie (3), Dr. Mohamed Koronfel (2), Prof. Mary Ryan (3), Prof. Marian Yallop (1), Prof. Alexandra Porter (3), Dr. Julia Parker (2), Dr. Paul Quinn (2)

Affiliations

1. Bristol University
2. Diamond Light Source Ltd.
3. Imperial College London

Keywords

ZnO and CeO₂ engineered nanomaterials 

in situ nano spectro-microscopy

nano-XANES, <75nm spatial resolution

ultrathin Raphidocelis subcapitata sections 

Abstract text

X-ray-based methodologies at Synchrotron facilities are versatile characterisation techniques for a wide range of scientific fields, offering a high penetration capability with relatively low cross sections when interacting with the analysed sample, making them suitable as non-destructive imaging and characterization methods at the (sub)micrometre scale. Scanning X-ray microscopy has become a widely applicable technique for evaluating the morphology of unknown samples (e.g. phase contrast, ptychography) as well as their chemical composition (e.g. fluorescence microscopy) and speciation (e.g. X-ray absorption spectroscopy, diffraction).

 

The incubation of engineered nanomaterials (ENMs) within aquatic environmental media and their potential internalisation in microorganisms (e.g. algae) are research areas which have benefited from the recent advances in nano spectro-microscopy. Spatially resolved transformations and speciation changes of nanomaterials can be studied by multi-energy X-ray absorption near-edge spectroscopy (XANES) analysis. In nano-XANES, the region of interest is repeatedly imaged while the energy in the incident beam is sequentially increased over the maximum of the absorption edge of the target element. This methodology provides the ability to generate image-stacks on the fluorescence detector, which can be translated into X-ray absorption spectra at each pixel. 

 

In this presentation, the transformation of ENMs after incubation within aquatic environmental media is described:

1) Synthetic zinc oxide (ZnO) template-growth nanorods (∼725 nm length, ∼140 nm diameter) were incubated in a range of real-world wastewater solutions. By applying in situ nano-XANES, real-time dissolution, morphological and chemical evolution of ZnO nanorods within short incubation times (1-3 hours) were observed [1] with a spatial resolution of ~100x100 nm per pixel.

2) Synthetic ceria (CeO₂) nanoparticles (∼9 nm) were aged and subsequently added to the green model algal species Raphidocelis subcapitata following the OECD recommendations, at CeO₂ concentrations that may be representative of hot-spots of diesel-pollution (~5 mg L^-1). The algae were later fixed by applying a high pressure freezing/freeze substitution protocol and resin embedded in Quetol. Ultrathin sections (100-200 nm thickness) were analysed by nano-XANES, after screening the regions with Ce-hotspots by X-ray fluorescence mapping.

 

Our results revealed significant Zn- and Ce-speciation changes after incubation and interaction with organics/algae, highlighting the need for time-resolved studies of nanomaterial transformations to evaluate the impact of these transformed species at the point of exposure to microorganisms. Fundamental knowledge of how the chemistry of the individual particles change, and the heterogeneity of transformations within hydrated systems, will reveal the critical physicochemical properties determining environmental damage and deactivation of engineered nanomaterials used in consumer products.

References

[1]        M. A. Gomez-Gonzalez et al., ACS Nano, vol. 13, no. 10, pp. 11049–11061, Oct. 2019.