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Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is expected to contribute to the evaluation of biomaterial surfaces interacting with proteins, cells and microbes because it requires no sample pre-treatments, such as labeling with probes and coating with metallic thin films for insulated samples. TOF-SIMS measurement provides chemical distribution of biomaterials with high spatial resolution. Since it is difficult for TOF-SIMS to generate enough characteristic secondary ions for imaging from large molecules such as proteins, multivariate analysis techniques such as principal component analysis (PCA) have been employed to characterize the spectra with fragment ions considered to be related to proteins. However, some of those fragment ions are also related to substrate especially polymers. Information theory was employed for the first time to analyze TOF-SIMS spectra of hollow-fiber dialysis membranes treated with a protein solution. TOF-SIMS spectra and images of protein adsorbed membranes and native membranes were compared based on mutual entropy in order to discriminate secondary ions related to protein from membranes. TOF-SIMS images with the fragment ion groups related to proteins and membrane were obtained respectively, and they show clearly the distribution of adsorbed protein on the dialysis membranes.

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