XPS analysis of bio‐organic systems

Abstract

A survey of the literature is made for the XPS analysis of food products (mainly spray-dried powders, which reveal a considerable surface enrichment in lipids) and of microorganisms and related systems (extracellular polymer substances and biofilms). This survey is used as a background for discussions and recommendations regarding methodology. Sample preparation methods reviewed are freeze drying, analysis of frozen hydrated specimens and adsorption of surface-active biocompounds on model substrates. Peak decomposition is a way to increase the wealth of information provided by the XPS spectra. It should be performed after a check that sample charge stabilization is satisfactory. Moreover, ensuring the precision needed to make comparisons within sets of samples may involve a trade-off between imposing constraints and generating information. The examination of correlations between spectral data in the light of chemical guidelines is useful to validate or improve peak decomposition and component assignment, and may also upgrade the chemical information regarding speciation. Further upgrading may be achieved by expressing marker XPS data in terms of concentrations of compounds of interest. Different methods of computation are discussed, providing a composition in terms of ingredients, classes of biochemical compounds, or various organic and inorganic compounds. As an alternative or complement to this deterministic approach, multivariate analysis of suitable spectral windows provides spectral components, which may be used for comparing samples, and which may have a direct chemical relevance or be used to identify features of interest.

Conditioning materials with biomacromolecules: Composition of the adlayer and influence on cleanability

“…In the case of the BSA sample, the additional carbon may also be due to compounds which are present as traces in the BSA solution and accumulate at the liquid-air interface upon evaporation of the solution drop during sample preparation. It is indeed well known that the surface of solid food products is strongly enriched in lipids compared to proteins (Rouxhet and Genet, 2011). It may be noted in Figure 5b that the amount of carbon not due to BSA is much higher for bare siliceous solids than for BSA-conditioned siliceous solids.…”

“…The C 1s peak was decomposed (Rouxhet et al, 2008;Rouxhet and Genet, 2011) with the S 2p 3/2 component near 163.7 eV, which was attributed to sulfur-containing residues of BSA (Caillou et al, 2007).…”

“…On the other hand, peak decomposition is an interpreting approach which involves a trade-off between imposing constraints and generating information (Rouxhet and Genet, 2011). Correlations between independent spectral data (elements, C 1s peak components) were used to validate peak decomposition and component assignment, and to identify useful markers for the determination of surface molecular composition.…”

Removing biofilms from stainless steel without changing surface properties relevant for bacterial attachment

“…The decreasing concentration of iron and chromium on the biofilm sample surface and the increased carbon concentration can be explained by the (carbon-containing) biofilm covering the surface. 13 Besides nitrogen, phosphorus can also be proof for bacteria on the surfaces. As phosphorus is a part of the DNA, it could be evidence for extracellular DNA.…”

Molecular level studies of polymer behaviors at the water interface using sum frequency generation vibrational spectroscopy

“…However, both XPS techniques require ultra-high vacuum. [33][34][35] Scanning electron microscopy and transmission electron microscopy provide a great deal of insight into polymer surface restructuring from water contact but require vacuum as well. 36,37 In addition, none of the aforementioned techniques can provide molecular orientation information at interfaces in situ.…”