Investigation of molecular surfaces with time-of-flight secondary ion mass spectrometry

TOF-SIMS is a promising technique for evaluating biodevices due to its ultrahigh surface sensitivity. Since a cluster ion source such as C(60)(+) provides low collision energy per atom, time-of-flight secondary ion mass spectrometry (TOF-SIMS) with the cluster ion is useful for detecting the uppermost surface of molecules immobilized on a substrate, and therefore, enables the evaluation of the orientation of these immobilized biomolecules. Effects of TOF-SIMS with C(60)(+) were investigated in this study. A relatively small protein, lysozyme, and polypeptides having five amino acid residues, Leu-enkephalin and Met-enkephalin, were employed as model samples. The protein and the polypeptides were immobilized on aminosilanized-indium-tin oxide (ITO) coated glass plates at their N-terminal residues by covalent bonding. The aminosilanized-ITO plate without protein or polypeptide was also prepared as a control sample. After freeze-drying, the samples were measured with TOF-SIMS using gallium and C(60)(+) cluster ion sources, and then TOF-SIMS spectra were analyzed to select peaks specific to each biomolecule by a comparison between the samples. As a result, the C(60)(+) primary ion source showed advantages in evaluating biomolecules, because more peaks at a higher mass generated from the biomolecules can be obtained using C(60)(+) than Ga(+) or Au(3)(+) as the primary ion source, although no difference was detected between the two polypeptide samples under the current measurement conditions. Copyright (C) 2010 John Wiley & Sons, Ltd.