Commercial Silicon-on-Insulator (SOI) Wafers as a Versatile Substrate for Laser Desorption/Ionization Mass Spectrometry

We report here that a commercial silicon-on-insulator (SOI) wafer offers an opportunity for laser desorption/ionization (LDI) of peptide molecules, which occurs directly from its flat surface without requiring special surface preparation. The LDI-on-SOI exhibits intact ionization of peptides with a good detection limit of lower than 20 fmol, of which the mass range is demonstrated up to insulin with citric acid additives. The LDI process most likely arises from laser-induced surface heating promoted by two-dimensional thermal confinement in the thin Si surface layer of the SOI wafer. As a consequence of the thermal process, the LDI-on-SOI method is also capable of creating post-source decay (PSD) of the resulting peptide LDI ions, which is suitable for peptide sequencing using conventional TOF/TOF mass spectrometry. © 2012 American Society for Mass Spectrometry.

A Method for Absolute Determination of the Surface Areal Density of Functional Groups in Organic Thin Films

To develop a methodology for absolute determination of the surface areal density of functional groups on organic and bio thin films, medium energy ion scattering (MEIS) spectroscopy was utilized to provide references for calibration of X-ray photoelectron spectroscopy (XPS) or Fourier transformation-infrared (FT-IR) intensities. By using the MEIS, XPS, and FT-IR techniques, we were able to analyze the organic thin film of a Ru dye compound (C58H86O8N8S2Ru), which consists of one Ru atom and various stoichiometric functional groups. From the MEIS analysis, the absolute surface areal density of Ru atoms (or Ru dye molecules) was determined. The surface areal densities of stoichiometric functional groups in the Ru dye compound were used as references for the calibration of XPS and FT-IR intensities for each functional group. The complementary use of MEIS, XPS, and FT-IR to determine the absolute surface areal density of functional groups on organic and bio thin films will be useful for more reliable development of applications based on organic thin films in areas such as flexible displays, solar cells, organic sensors, biomaterials, and biochips.

Identification of donor deactivation centers in heavily As-doped Si using time-of-flight medium-energy ion scattering spectroscopy

Electrically-inactive arsenic (As) complexes in silicon are investigated using time-of-flight medium-energy ion scattering spectroscopy. In heavily As-doped Si, the As atoms that are segregated in the Si interface region just below the SiO2 are found to be in interstitial forms (Asi), while the As atoms in the bulk Si region are found to be in the substitutional form (AsSi). Despite the substitutional form of As, most of the As are found to be electrically inactive in the bulk region, and we identify the As to be in the form of a 〈111〉-oriented AsSi-Si-vacancy (AsSi-VSi) complex. The Asi atoms in the interface Si region are found to exist together with Si-interstitial atoms (Sii), suggesting that the Asi atoms in the interface Si region accompany the Sii atoms. © 2015 AIP Publishing LLC.

Vascular-Inducing Poly(glycolic acid)-Collagen Nanocomposite-Fiber Scaffold

For regenerative medicine with scaffolds, the immediate cellularization of the scaffold accompanied by angiogenesis inside is an important event. Such the aim is generally pursued by combining basic fibroblast growth factor (b-FGF) or vascular endothelial growth factor (VEGF) with the scaffold. In this study, we produced the nanocomposite nanofiber composed of poly(glycolic acid), PGA, and collagen to accomplish the recruitment of host cells and peripheral blood vessels without the bio-derived matter like growth factors. Structural analysis revealed that the fiber has the sheath-core like structure in which the surface region is abundant in PGA and the core region is abundant in collagen. This peculiar fibrous structure probably contributes the fragility of the fiber under the swelling in body fluid. The results of the animal experiment demonstrated that the PGA-collagen nanofiber sponge was entirely populated and vascularized within 5 days after the implantation. We hypothesized that the early fragmentation of the implanted fibrous sponge accelerated the host's inflammation reaction by phagocytized by macrophage, which followed by the recruitment of the fibroblasts and endothelial cells from the host tissue. Designing the suitable nanoscale structure of materials makes cellularization and vascularization of the scaffold possible without bio-derived factors. Copyright © 2013 American Scientific Publishers All rights reserved.

Lipid crystals mechanically stimulate adjacent extracellular matrix in advanced atherosclerotic plaques

Objective: Although lipid crystals (LCs) have received attention as a causative factor of plaque rupture, the mechanisms by which they increase plaque vulnerability are unknown. We examined whether solid-state LCs physically affect the adjacent extracellular matrix (ECM) using a combination of multimodal nonlinear optical (MNLO) imaging and finite element analysis (FEA). Methods: The changes of ECMs affected by lipids in atherosclerotic arteries in apolipoprotein E-deficient mice (n=32) fed a high-fat diet for 20-30 weeks were micro-anatomically visualized by a 3D MNLO imaging platform including CARS for lipids, TPEF for elastin, and SHG for collagen. Results and Conclusion: The TPEF signal of elastin was increased at the peripheral regions of LCs (<10μm) compared with foam cell regions. In order to confirm the increase of elastin, biochemical assay (western blot) was performed. The protein level of elastin was increased approximately 2.25-fold (p=0.024) in LC-rich arteries. Under the hypothesis that the increase of elastin resulted from the mechanical stimulus from solid-state LCs, MNLO images were subjected to FEA to simulate the displacement according to the expanding magnitude of the vessel during cardiac cycles. We found that microscale focal stress was increased specifically around the LCs. These FEA results corresponded with the increase of elastin observed by TPEF. These data suggest that LCs mechanically stimulate the adjacent ECM to alter the composition of ECM and cause vessel remodeling. The combination of MNLO imaging and FEA has great potential to verify the mechanical predictions in cardiovascular diseases. © 2014 Elsevier Ireland Ltd.