Correlative high resolution microscopy and mass spectrometry for morphological and chemical analysis of nanoparticles in biological systems

Combined morphological and chemical analysis of ultrastructures is gaining more and more attention in both material and life sciences. Especially the detection of nanoparticles within biological tissue has become a hot topic in environmental research, ecology, nanotoxicology, but also medicine and life science using nanoparticles as carriers for therapeutic drugs. Usually, several highly specialised instruments have to be used to investigate the respective key features of the sample.
Here, a new prototype instrument is presented that combines sub20nm SIMS on a helium ion microscope [HIM; 1] with dark and bright field imaging in one tool – the npSCOPE [2]: the multi-modal instrument couples a Gas Field Ion Source (GFIS) as primary ion beam source with a secondary ion mass spectrometer (SIMS) system featuring a continuous focal plane detector (FPD) and a STHIM detector for imaging the transmitted helium beam. The latter allows investigation of thin samples like biological tissue sections. For morphological/topographical analysis of charging and non-charging bulk samples with sub-nm resolution, the instrument is also equipped with a secondary electron detector and a flood gun. This setup allows (a) higher sensitivity than analytical electron microscopy combined with (b) better spatial resolution than available with other SIMS methodologies typically used for life science questions. The FPD yields a full mass spectrum per scanned pixel featuring the possibility of post hoc analysis of all elements/ion species detected.
Several examples will be presented to show how thin tissue sections can first be investigated with transmitted ions for proper contrast of biological membranes followed by chemical characterization of associated or ingested nanoparticles without the need to transfer samples between different instruments. Specific localisation of the nanoparticles outside the cell membrane or within the cytoplasm or subcellular compartments can be obtained.

In summary, a unique tool for all-in-one physico-chemical characterisation of nanoparticles both before contact to a living organism and after incorporation is presented. Pixel by pixel correlation of the different datasets are directly obtained by image fusion or co-registration methods. For future analysis of frozen-hydrated samples, a cryo-stage is currently being integrated into the npSCOPE. It will yield close to native chemical analysis of diagnostic, environmental and nanotoxicology samples with decreased experiment times and without artefacts due to sample transfer.
References:
[1] T. Wirtz, O. De Castro, J.-N. Audinot, P. Philipp. Imaging and analytics on the Helium Ion Microscope. Annual Review of Analytical Chemistry 12 (2019) 523-543

[2] This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 720964.