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

Abstract

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.

Evaluation of immobilized polypeptides with different C‐terminal residues using argon gas‐cluster SIMS

“…Therefore, it is indicated that the argon GC‐SIMS detects differences between the surface residues of the immobilized‐polypeptide molecules. Moreover, there was no difference in the peak at m/z 136 between the two enkephalins detected using conventional primary ion sources, such as Ga + and C 60 + 15…”