Prominent resonance Raman and photoluminescence spectroscopic differences between AA′ and AB stacked bilayer molybdenum disulfide (MoS2) grown by chemical vapor deposition are reported. Bilayer MoS2 islands consisting of the two stacking orders were obtained under identical growth conditions. Resonance Raman and photoluminescence spectra of AA′ and AB stacked bilayer MoS2 were obtained on Au nanopyramid surfaces under strong plasmon resonance. Both resonance Raman and photoluminescence spectra show distinct features indicating clear differences in interlayer interaction between these two phases. The implication of these findings on device applications based on spin and valley degrees of freedom will be discussed.

Ultrasensitive detection and spatially resolved mapping of neurotransmitters, dopamine and serotonin, are critical to facilitate understanding brain functions and investigate the information processing in neural networks. In this work, we demonstrated single molecule detection of dopamine and serotonin using a graphene–Au nanopyramid heterostructure platform. The quasi-periodic Au structure boosts high-density and high-homogeneity hotspots resulting in ultrahigh sensitivity with a surface enhanced Raman spectroscopic (SERS) enhancement factor ∼1010. A single layer graphene superimposed on a Au structure not only can locate SERS hot spots but also modify the surface chemistry to realize selective enhancement Raman yield. Dopamine and serotonin could be detected and distinguished from each other at 10–10 M level in 1 s data acquisition time without any pretreatment and labeling process. Moreover, the heterostructure realized nanomolar detection of neurotransmitters in the presence of simulated body fluids. These findings represent a step forward in enabling in-depth studies of neurological processes including those closely related to brain activity mapping (BAM).

Summary Mammalian tissues calcify with age and injury. Analogous to bone formation, osteogenic cells are thought to be recruited to the affected tissue and induce mineralization. In the heart, calcification of cardiac muscle leads to conduction system disturbances and is one of the most common pathologies underlying heart blocks. However the cell identity and mechanisms contributing to pathological heart muscle calcification remain unknown. Using lineage tracing, murine models of heart calcification and in vivo transplantation assays, we show that cardiac fibroblasts (CFs) adopt an osteoblast celllike fate and contribute directly to heart muscle calcification. Small molecule inhibition of ENPP1, an enzyme that is induced upon injury and regulates bone mineralization, significantly attenuated cardiac calcification. Inhibitors of bone mineralization completely prevented ectopic cardiac calcification and improved post injury heart function. Taken together, these findings highlight the plasticity of fibroblasts in contributing to ectopic calcification and identify pharmacological targets for therapeutic development.

Surface-enhanced Raman spectroscopy (SERS) is a surface-sensitive technique that can enhance the intensity of Raman signal by several orders of magnitude, enabling even the detection of single molecule. This work presents the experimental and theoretical studies of an optical fiber probe with nano-structured end-facet for bio-sensing applications via SERS. The factors affecting the intensity of Raman signal passing through the fiber probe are investigated. These factors include the numerical aperture of the objective lens, the slit width of the spectrometer, the fiber length, and the size of SERS nano-array. The Raman signal loss through fiber compared with optical microscope-based free-space Raman detection is estimated. To further enhance the SERS enhancement factor, a hybrid graphene/Au nano-triangle structure is transferred on the end-facet of the fiber probe to enable SERS. Superimposing graphene layer on Au nano-structure is found to be superior over bare Au nano-structure in terms of the detection sensitivity.

By using finite-difference time-domain simulation, we investigate the enhancement of local electrical field by combining localized surface plasmon (LSP) of Au nanopyramid array and surface plasmon polaritons (SPPs) focused by Au nanorings. We report on the systematic investigation of structural variables that could affect the coupling efficiency between SPPs and LSP to obtain optimal design. The study aims at finding the quasi-quantitative relation between several key-variables of the pyramid-ring combination and the overall surface enhanced Raman spectroscopy (SERS) enhancement at the center of the structure. We consider the following factors that could affect the interaction between SPPs and LSP: ring radius, number of rings, pyramid spacing, number of pyramids, and the relative position of ring center and pyramid array center. By adjusting these structural variables, high electric field enhancement of up to 140× and large volume of hot spots can be achieved. We also investigate the incorporation of the LSP−SPP hybrid structure onto the facet of optical fiber for SERS-based detection.

Two-dimensional (2D) materials, such as graphene and MoS 2 , have been attracting wide interest in surface enhancement Raman spectroscopy. This perspective gives an overview of recent developments in 2D materials' application in surface-enhanced Raman spectroscopy. This review paper focuses on the applications of using bare 2D materials and metal/2D material hybrid substrate for Raman enhancement. The Raman enhancing mechanism of 2D materials will also be discussed. The progress covered herein shows great promise for widespread adoption of 2D materials in SERS application.

No abstract

Amyloid β-protein (Aβ) self-association is one process linked to the development of Alzheimer's disease (AD). Aβ peptides, including its most abundant forms, Aβ40 and Aβ42, are associated with the two predominant neuropathologic findings in AD, vascular and parenchymal amyloidosis, respectively. Efforts to develop therapies for AD often have focused on understanding and controlling the assembly of these two peptides. An obligate step in these efforts is the monitoring of assembly state. We show here that surface-enhanced Raman spectroscopy (SERS) coupled with principal component analysis (PCA) readily distinguishes Aβ40 and Aβ42. We show further, through comparison of assembly dependent changes in secondary structure and morphology, that the SERS/PCA approach unambiguously differentiates closely related assembly stages not readily differentiable by circular dichroism spectroscopy, electron microscopy, or other techniques. The high discriminating power of SERS/PCA is based on the rich structural information present in its spectra, which comprises not only on interatomic resonances between covalently associated atoms and hydrogen bond interactions important in controlling secondary structure, but effects of protein orientation relative to the substrate surface. Coupled with the label-free, single molecule sensitivity of SERS, the approach should prove useful for determining structure activity relationships, suggesting target sites for drug development, and for testing the effects of such drugs on the assembly process. The approach also could be of value in other systems in which assembly dependent changes in protein structure correlate with the formation of toxic peptide assemblies.