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Comparative study of the ToF‐SIMS, FT‐IR and XPS techniques for quantitative analyses of mixed self‐assembled monolayers

We present a comparative study of the time‐of‐flight‐secondary ion mass spectrometry (ToF‐SIMS), Fourier transform infrared (FT‐IR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) techniques on a mixed self‐assembled monolayer (SAM) of biotinylated polyethylene glycol alkane thiol (BPT) and 11‐mercaptoundecanol (MUD) as a model system. This mixed SAM was employed to maximize specific binding between the biotin groups in the mixed SAM and the streptavidin, while minimizing nonspecific adsorption of the streptavidin. For a better quantitative analysis of our mixed SAM by using ToF‐SIMS, we performed a principal component analyses (PCA) with various peak sets and found that the negative ions of the MUD complementary peak set showed good correlation between the XPS and FT‐IR quantification results and the scores for principal component 1 from a PCA of the ToF‐SIMS data. These findings show that ToF‐SIMS analysis along with PCA would make a good surface analysis technique for identifying intact molecules of adsorbates and for quantifying at once each adsorbate in a mixed SAM. Copyright © 2014 John Wiley & Sons, Ltd.