Abstract
Monitoring of protein distribution on material surfaces is required for developing high performance materials. In this study, distributions of protein A immobilized on glass plates were monitored by means of a new protein monitoring technique based on time-of-flight secondary ion mass spectrometry (TOF-SIMS), which provides specific chemical imaging. Especially for protein analysis, appropriate analysis techniques of TOF-SIMS data are required for discrimination among proteins because most of fragment ions from proteins by TOF-SIMS are the same. In this study information entropy was applied to characterize TOF-SIMS spectra of protein samples containing similar fragment ions. Mutual information, calculated as subtraction of a posteriori information entropy from a priori information entropy indicates specific secondary ion peaks related to a certain protein in spectra. TOF-SIMS spectra and images of the protein immobilized on glass plates were obtained with TFS-2100 (Physical Electronics). TOF-SIMS spectra were analyzed by this method and then specific fragment ions from protein A and glass plates, respectively, are selected according to values of mutual information. With specific fragment ions of each protein, TOF-SIMS image of each protein was obtained. Distributions of protein A on glass plates are obtained with this method.
