Abstract
Since Ar-gas cluster ion beams (Ar-GCIBs) have been introduced into time-of-flight secondary ion mass spectrometry (ToF-SIMS), there have been various attempts to analyze organic materials and biomolecules that require low-damage analysis and high sensitivity, because Ar-GCIBs allow soft ionization of large molecules such as peptides and proteins due to the low energy per atom. Here, the authors adopted the Ar-GCIB as a primary beam to detect proteins including human insulin, ubiquitin, and cytochrome C (molecular weights are 5808, 8564, and 12 327 Da, respectively). They have confirmed that the detection of the intact proteins was possible when the Ar-GCIB was used as a primary ion beam. In addition, they successfully identified each protein by analyzing the trypsin-digested peptides in myoglobin, cytochrome C, and bovine serum albumin. They also attempted on-surface enzymatic digestion to identify proteins on the surface of the Si wafer and obtained results identical to those of in-solution digestion. It is expected that the authors' on-surface digestion method can enable the application of ToF-SIMS for the analysis of proteins present in biological tissues.
Highlights
Gas cluster ion beams (GCIBs) were introduced as a projectile for time-of-flight secondary ion mass spectrometry (ToF-SIMS) because the numerous constituent atoms reduce the energy per atom
Ar-GCIB with a cluster size of 2000 and an acceleration voltage of 20 kV was applied to protein samples
It was confirmed that intact insulin, ubiquitin, and cytochrome C were able to be detected when Ar-GCIB was used as a primary ion beam
Summary
Gas cluster ion beams (GCIBs) were introduced as a projectile for time-of-flight secondary ion mass spectrometry (ToF-SIMS) because the numerous constituent atoms reduce the energy per atom. it is expected that the cluster ion beam can reduce sample damage, improve sputtering yield, and increase secondary ion intensity. By controlling the number of gas clusters, the energy per atom can be adjusted from several eV to several tens of eV, and the sputtering yield of the neutral material from organic materials and polymers can be 4 orders higher than those of atomic solids such as Si, SiO2, and Au. By using incident energy of this range to sputter the samples, ToF-SIMS analysis with reduced subsurface damage and minimal interlayer mixing can be performed on organic materials and biomolecules.. Gas cluster ion beams (GCIBs) were introduced as a projectile for time-of-flight secondary ion mass spectrometry (ToF-SIMS) because the numerous constituent atoms reduce the energy per atom.. By using incident energy of this range to sputter the samples, ToF-SIMS analysis with reduced subsurface damage and minimal interlayer mixing can be performed on organic materials and biomolecules.. GCIBs have been applied to depth profiling of the organic film, analysis of peptides and proteins, and imaging of biological tissues.. We successfully detected intact proteins with a molecular weight of over 10 000 Da by using Ar-GCIBs. In addition, we identified myoglobin, cytochrome C, and bovine serum albumin (BSA), where the samples were prepared by a conventional method, which is based on the tryptic digestion of the proteins in-solution. We expect that our new strategy to analyze proteins on-surface by using Ar-GCIBs can provide new opportunities for bottom-up proteomics in the ToF-SIMS analysis
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