Characterization of sequentially grafted polysaccharide coatings using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and principal component analysis (PCA)

Abstract

Sequentially grafted polymer layers are playing an increasingly important role in a variety of biomedical applications. Characterization of the chemistry and structure of these coatings has typically followed a layer-by-layer approach, ignoring potential interactions between the adjacent layers and the effects that these interactions may have on the resulting physicochemical characteristics of the surface. Using a sequential grafting protocol to couple the polysaccharide carboxymethyldextran (CMD), previous surface force and x-ray photoelectron spectroscopy studies have suggested that there was some intercalation of the CMD and intermediate poly(ethyleneimine) (PEI) layers. We have utilized the surface and chemical specificity of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate the intercalation of the polymer layers. Owing to the complexity of the data, principal component analysis (PCA) was used to interpret the spectra of the grafted polymer films. The results of the PCA indicated that variations between spectra could be related directly to the carboxyl density (1 : 2 or 1 : 30 carboxyls per glucose unit) of the CMD. Variations between the spectra were shown to be due to the presence of nitrogen-rich species from the PEI at the outermost surface in the CMD 1 : 30 samples, whereas the CMD 1 : 2 spectra contained oxygen-rich species related to the presence of the polysaccharide. These results enabled a model to be developed combining the new data with the previous studies to show the carboxyl-density-dependent intercalation of the CMD and PEI layers in this polymer graft. The application of ToF-SIMS and PCA allowed conclusive determination of the surface structure of this complex grafted polymer layer.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS):—versatility in chemical and imaging surface analysis

“…Castner's group has successfully applied PCA analysis to identifying various adsorbed protein films, separating them out from very similar spectra, which would be virtually impossible to separate out visually. [17][18][19] Vanden Eynde and Bertrand have also applied PCA analysis for the quantification of polystyrene spectra. 20 While PCA generally is an "unsupervised" variational recognition technique, "supervised" pattern recognition techniques such as discriminant PCA 21 can further enhance the ability to distinguish between various spectra.…”

Surface studies of halloysite nanotubes by XPS and ToF‐SIMS

“…The use of a statistical tool, such as principal component analysis (PCA), to analyze the spectra can yield very useful information. PCA, which can easily convert a large number of mass peaks into a few simple datasets, has been widely used in surface analyses of inorganic compounds,22, 23 adsorbed proteins24 and polymers 25, 26…”

Molecular Determination of Organic Adsorption Sites on Smectite during Fe Redox Processes Using ToF-SIMS Analysis

“…oneidensis MR-1 cells and/or their metabolites was adsorbed to the surface of NAu-2 and was not detached by subsequent PPHA adsorption. These signals were commonly found in polysaccharides and amino acids, , suggesting EPS (rich in polysaccharides, also containing a small amount of protein and DNA) as the main component in the adsorbed MC. Indeed, EPS can be extensively produced by many microorganisms including Shewanella and are commonly observed to abundantly adhere to clay particles. , The functional groups of EPS on BR-NAu-2 were also observed with FTIR (Figure S7).…”