Imaging XPS and photoemission electron microscopy; surface chemical mapping and blood cell visualization

Abstract

Combined photoemission electron microscopy (PEEM) and imaging x-ray photoelectron spectroscopy (XPS), i.e., electron spectroscopy for chemical analysis in the nanoregion, has been used for surface characterization of bio-relevant and biological samples. In the first example, the authors prepared a gold patterned silicon substrate, stepwise surface modified by self-assembled monolayers followed by quantum dot (QDot) specific linking and investigated by means of work function mapping and elemental imaging in the submicrometer range. Spatially resolved core level images of C1s, V2p, and Y3d are obtained, which verify the selective thiol adsorption on the gold squares and specific binding of europium doped yttrium vanadate QDots on the self-assembled monolayer. The second example is platelet adhesion to Immunoglobulin G modified silicon surfaces, investigated by means of laterally resolved PEEM. Images of platelets clearly show activated cells with a morphology change including an enlarged surface area and elongated pseudopodia, with a lateral resolution of 140 nm. In the last example, neutrophils were allowed to attach to plain silicon surfaces and investigated by means of PEEM and imaging XPS. Here, the cells show a round shaped morphology, as expected. Threshold imaging with work function contrast is used to localize the area of interest, followed by elemental specific mapping on cells in the submicrometer region. Chemical shifts of C1s in photoemission are used to distinguish vital parts of the cell structure. The strong C1s (C-C) signal is achieved from the region of the cell membrane, i.e., high density of phospholipids, while C1s (C-N) and C1s (C-O) signals are obtained from the core of the cell, in good agreement with the presence of cytoplasm and deoxyribonucleic acid containing cell nucleus. The combination of PEEM and imaging XPS is shown here as a tool to deliver new insight into biological samples, i.e., a rapid sample overview is obtained based on low energy secondary electrons with work function contrast, followed by detailed studies in the narrow mode for elemental compositions based on photoemission. This study illustrates the strength of combined PEEM and XPS in the imaging mode on cell studies.

Chemical characterization of red cells from the black sea urchin Arbacia lixula by X-ray photoelectron spectroscopy

“…6 Moreover the colorless cells are characterized, from oxygen expected functional groups compatible with protein, phospholipide and (lipo)-polysaccharides molecules, according to the cellular membrane surface composition in the external depth of 5-10 nm detectable by XPS analysis on similar cells. 14,16,38 signals have been reported in Fig. 5 (panels A and B).…”

“…15 More recently, analysis by nano-ESCA (Electron Spectroscopy for Chemical Analysis) of biological samples, such as blood cells (i.e., neutrophil and platelets) immobilized on suitable surfaces, have been reported for chemical and morphological cell studies, showing that these typologies of bio-organic sample can be analyzed in a condition of ultra-high-vacuum (UHV). 16 As an example, in a successful study, the chemical differences between the membrane and the cytoplasm of dehydrated neuronal cells immobilized on gold surface have been reported. 14 However, to our knowledge it does not appear that XPS studies has been applied specically and systematically to characterize purely biological systems, as coelomocytes from sea urchins, bio-adsorbed on a coverslip and de-hydrated in N 2 atmosphere.…”

Photoemission and Characterization of Neutrophils and Nanoparticles : Energy Mapping and Elemental Composition with sub-µm Resolution

“…The ability to image and visualize cells and tissues with chemical composition on the cellular and subcellular level will broaden and increase our knowledge of biological relevant problems and biological processes. [3][4][5][6][7] There is a need for well suited label-free and non-destructive analytical imaging tools for imaging biological samples such as cells attached to surfaces, cellular morphologies, interactions between cells, receptors expressed at the cell surface, to address biological processes on the cellular level. 4,8 Photoemission electron microscopy (PEEM) and X-ray photoelectron spectroscopy (XPS) are two unique surface sensitive analytical instruments, based on the photoemission process, that are used for surface characterization and are today, frequently used and have shown great potential in classical surface physics and material science.…”

“…[3][4][5][6][7] There is a need for well suited label-free and non-destructive analytical imaging tools for imaging biological samples such as cells attached to surfaces, cellular morphologies, interactions between cells, receptors expressed at the cell surface, to address biological processes on the cellular level. 4,8 Photoemission electron microscopy (PEEM) and X-ray photoelectron spectroscopy (XPS) are two unique surface sensitive analytical instruments, based on the photoemission process, that are used for surface characterization and are today, frequently used and have shown great potential in classical surface physics and material science. Hard materials such as thin films, semiconductors and nanomaterials [9][10][11][12][13] but also soft materials such as organo-materials and polymers are a few examples where PEEM and XPS characterization have shown great value.…”

“…Local variations in the electron emission are utilized in PEEM to generate images with work function contrast on the nanoscale dimension. 4 NanoESCA is an instrument that combines these two techniques and has the potential to be extended as a label-free specific analytical imaging tool for characterization and visualization of biological samples.…”