Thermal conductivity of suspended pristine graphene measured by Raman spectroscopy

The thermal conductivity of suspended single-layer graphene was measured as a function of temperature using Raman scattering spectroscopy on clean samples prepared directly on a prepatterned substrate by mechanical exfoliation without chemical treatments. The temperature at the laser spot was monitored by the frequency of the Raman 2$D$ band of the Raman scattering spectrum, and the thermal conductivity was deduced by analyzing heat diffusion equations assuming that the substrate is a heat sink at ambient temperature. The obtained thermal conductivity values range from $\sim$1800 Wm$^{-1}$K$^{-1}$ near 325 K to $\sim$710 Wm$^{-1}$K$^{-1}$ at 500 K.Comment: 4pages, 3 figure

4-O-Carboxymethylascochlorin Inhibits Expression Levels of on Inflammation-Related Cytokines and Matrix Metalloproteinase-9 Through NF–κB/MAPK/TLR4 Signaling Pathway in LPS-Activated RAW264.7 Cells

Toll-like receptor 4 (TLR4) and matrix metalloproteinase-9 (MMP-9) are known to play important roles in inflammatory diseases such as arteriosclerosis and plaque instability. The purpose of this study was to perform the effect of 4-O-carboxymethylascochlorin (AS-6) on MMP-9 expression in lipopolysaccharide (LPS)-induced murine macrophages and signaling pathway involved in its anti-inflammatory effect. Effect of AS-6 on MAPK/NF-κB/TLR4 signaling pathway in LPS-activated murine macrophages was examined using ELISA, Western blotting, reverse transcription polymerase chain reaction (RT-PCR) and fluorescence immunoassay. MMP-9 enzyme activity was examined by gelatin zymography. AS-6 significantly suppressed MMP-9 and MAPK/NF-κB expression levels in LPS-stimulated murine macrophages. Expression levels of inducible nitric oxide synthase (iNOS), COX2, MMP-9, JNK, ERK, p38 phosphorylation, and NF-κB stimulated by LPS were also decreased by AS-6. Moreover, AS-6 suppressed TLR4 expression and dysregulated LPS-induced activators of transcription signaling pathway. The results of this study showed that AS-6 can inhibit LPS-stimulated inflammatory response by suppressing TLR4/MAPK/NF-κB signals, suggesting that AS-6 can be used to induce the stability of atherosclerotic plaque and prevent inflammatory diseases in an in vitro model

Graphene nano-electromechanical mass sensor with high resolution at room temperature

The inherent properties of 2D materials—light mass, high out-of-plane flexibility, and large surface area—promise great potential for precise and accurate nanomechanical mass sensing, but their application is often hampered by surface contamination. Here we demonstrate a tri-layer graphene nanomechanical resonant mass sensor with sub-attogram resolution at room temperature, fabricated by a bottom-up process. We found that Joule-heating is effective in cleaning the graphene membrane surface, which results in a large improvement in the stability of the resonance frequency. We characterized the sensor by depositing Cr metal using a stencil mask and found a mass-resolution that is sufficient to weigh very small particles, like large proteins and protein complexes, with potential applications in the fields of nanobiology and medicine.</p

Layer number identification of CVD-grown multilayer graphene using Si peak analysis

Abstract Since the successful exfoliation of graphene, various methodologies have been developed to identify the number of layers of exfoliated graphene. The optical contrast, Raman G-peak intensity, and 2D-peak line-shape are currently widely used as the first level of inspection for graphene samples. Although the combination analysis of G- and 2D-peaks is powerful for exfoliated graphene samples, its use is limited in chemical vapor deposition (CVD)-grown graphene because CVD-grown graphene consists of various domains with randomly rotated crystallographic axes between layers, which makes the G- and 2D-peaks analysis difficult for use in number identification. We report herein that the Raman Si-peak intensity can be a universal measure for the number identification of multilayered graphene. We synthesized a few-layered graphene via the CVD method and performed Raman spectroscopy. Moreover, we measured the Si-peak intensities from various individual graphene domains and correlated them with the corresponding layer numbers. We then compared the normalized Si-peak intensity of the CVD-grown multilayer graphene with the exfoliated multilayer graphene as a reference and successfully identified the layer number of the CVD-grown graphene. We believe that this Si-peak analysis can be further applied to various 2-dimensional (2D) materials prepared by both exfoliation and chemical growth

Nanoscale Structural Switching of Plasmonic Nanograin Layers on Hydrogel Colloidal Monolayers for Highly Sensitive and Dynamic SERS in Water with Areal Signal Reproducibility

Developing substrates that enable both reproducible and highly sensitive Raman detection of trace amounts of molecules in aqueous systems remains a challenge, although these substrates are crucial in biomedicine and environmental sciences. To address this issue, we report spatially uniform plasmonic nanowrinkles formed by intimate contact between plasmonic nanograins on the surface of colloidal crystal monolayers. The Au or Ag nanograin layers coated on hydrogel colloidal crystal monolayers can reversibly wrinkle and unwrinkle according to changes in the water temperature. The reversible switches are directed by surface structural changes in the colloidal crystal monolayers, while the colloids repeat the hydration–dehydration process. The Au and Ag nanowrinkles are obtained upon hydration, thus enabling the highly reproducible detection of Raman probes in water at the nano- and picomolar levels, respectively, throughout the entire substrate area. Additionally, the reversible switching of the nanostructures in the plasmonic nanograin layers causes reversible dynamic changes in the corresponding Raman signals upon varying the water temperature

Graphene nano-electromechanical mass sensor with high resolution at room temperature

The inherent properties of 2D materials—light mass, high out-of-plane flexibility, and large surface area—promise great potential for precise and accurate nanomechanical mass sensing, but their application is often hampered by surface contamination. Here we demonstrate a tri-layer graphene nanomechanical resonant mass sensor with sub-attogram resolution at room temperature, fabricated by a bottom-up process. We found that Joule-heating is effective in cleaning the graphene membrane surface, which results in a large improvement in the stability of the resonance frequency. We characterized the sensor by depositing Cr metal using a stencil mask and found a mass-resolution that is sufficient to weigh very small particles, like large proteins and protein complexes, with potential applications in the fields of nanobiology and medicine.Dynamics of Micro and Nano SystemsBN/Chirlmin Joo La