Neutrophils Activated by Nanoparticles and Formation of Neutrophil Extracellular Traps: Work Function Mapping and Element Specific Imaging.

Photoemission electron microscopy (PEEM) and imaging X-ray photoelectron spectroscopy (XPS) have over the years been powerful tools in classical surface physics and material sciences, and due to recent technological advances, their uses within other fields/disciplines are rapidly growing. Lately, the XPS/PEEM based elemental analysis and characterization in imaging mode, with exquisite spatial resolution and high sensitivity, has shown the potential to deliver new mechanistic insights in cell-biology/medicine. In this work, the aim was to visualize biological processes on the cellular level, with the additional dimension of topographical morphology and element specific information, mapping chemical composition and chemical states. This is hereby demonstrated by combined PEEM and imaging XPS investigation of neutrophils and their activation processes, where fluorescence microscopy commonly used in biology is used for benchmarking. Neutrophils are phagocytic cells and are vital components in the human immune system, with the fundamental role of fighting invading pathogens. They are capable of ingesting microorganisms or particles, and in order to capture and trap foreign objects, one of their strategies is to release nuclear DNA by the formation of extracellular web-like traps (NETs). Here, we report how neutrophils are triggered by controlled nanoparticle (NP) exposure. The neutrophils and NETs formation are imaged in the presence of NPs, and we report the elemental composition of single cells and the structure of NETs. Cellular uptake of nanoparticles is proven and the states just before and after NETs release are imaged, as well as visualization of the extraordinary capability for mass transport at distances 10 times or more than the size of the cell itself. This method paves the way for element specific imaging of biorelated cells on surfaces as well as nanoparticle tracking in the submicro- and nanoregions.