The presence of two sulfur species was detected in X-ray photoelectron spectroscopy (XPS) studies of thiol and disulfide molecules adsorbed onto gold surfaces. These species are assigned to bound thiolate (S2p3/2 binding energy of 162 eV) and unbound thiol/disulfide (S2p3/2 binding energy from 163.5 to 164 eV). These assignments are consistent with XPS data obtained from different thiols (C12, C16, C18, and C22 alkane thiols, a fluorinated thiol, and a cyclic polysiloxane thiol) and different adsorption conditions (solvent type, thiol concentration, temperature, and rinsing). In particular, the use of a poor solvent for thiol adsorption solutions (e.g., ethanol for long chain alkanethiols) and the lack of a rinsing step both resulted in unbound thiol molecules present at the surface of the bound thiolate monolayer. This has implications for recent studies asserting the presence of multiple binding sites for gold-thiolate species in organic monolayers.

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Characterization of the adsorbed protein film that forms upon implantation of a biomedical device is a long-standing interest in biomaterials research. Time-of-flight secondary ion mass spectrometry (ToF−SIMS) is a powerful method for the characterization of adsorbed proteins on biomaterial surfaces due to its chemical specificity and surface sensitivity. However, the SIMS fragmentation patterns for proteins are quite complex due to the heterogeneity of the protein sequence. Therefore, the multivariate analysis technique principal components analysis (PCA) was used to obtain a more detailed interpretation of the protein SIMS spectra. This study utilizes single component adsorbed protein films on three model substrates and multivariate analysis of the ToF−SIMS data to determine the identity of protein films. Furthermore, ToF−SIMS and PCA were used to give insight into the composition of a 1% bovine plasma protein film. The single component spectra from 13 different proteins were readily distinguishable using PCA. The major component of the 1% bovine plasma film was found to shift from fibrinogen to γ-globulins over the course of 2 h, in agreement with the current literature. This study shows how combination of ToF−SIMS and PCA provides new insights into the composition of adsorbed protein films on biomaterial surfaces.

XPS spectra of nine model polymers containing oxygen functional groups are studied. The measured 0 Is binding energies were 532.8 eV for ether and alcohol oxygens, 5322 eV for ketone oxygens and 532.2 and 533.7 eV for the carbonyl-and ether-type oxygens in ester groups, respectively. Comparison with previous experimental and theoretical 0 1s binding energies for these group is also presented. Absolute 0 1s binding energies of polymers are not in agreement with those published by other groups. However, with the exception of ketone oxygens, binding energy shits observed for the various functional groups are comparable.

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