Review of TOF-SIMS bioanalysis using mutual information

The evaluation of proteins on biodevices, such as the distribution or orientation of immobilized proteins, is one of the most important issues for the development of sophisticated biodevices. In this review, a description is provided of the application of one of the most sensitive surface analysis methods, time-of-flight secondary ion mass spectrometry (TOF-SIMS), to protein evaluation and TOF-SIMS spectra analysis using mutual information. TOF-SIMS is useful for the evaluation of biodevice surfaces, because TOF-SIMS provides submicron-scale chemical mapping and information on the chemical structures of the upper surface part of a protein. In addition, TOF-SIMS requires no pretreatment of samples, such as labeling with a fluorescent probe or coating with metallic thin films. Data analysis methods are, however, required to interpret the protein sample TOF-SIMS data, because the fragment ions from proteins are so complicated that it is difficult to predict them. In order to identify hidden important peaks related to protein samples out of the hundreds of peaks in TOF-SIMS spectra, mutual information has been used. Protein distribution on biodevices and the orientation of an immobilized protein obtained with this method are described in this review. Copyright (C) 2008 John Wiley & Sons, Ltd.