Characterization of Adsorbed Protein Films by Time-of-Flight Secondary Ion Mass Spectrometry with Principal Component Analysis

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.