We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460 μJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×10(19) W/cm(2)) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.
Surface plasmons on isolated gold dimers can initiate intermolecular reactions of adsorbed p-nitrothiophenol. At the single molecule level when dimerization is not possible an intramolecular reaction can be observed. Experimental evidence indicates that plasmon-induced hot electrons provide the required activation energy.
The formation of insoluble β-sheet-rich protein structures known as amyloid fibrils is associated with numerous neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease. A detailed understanding of the molecular structure of the fibril surface is of interest as the first contact with the physiological environment in vivo and plays a decisive role in biological activity and associated toxicity. Recent studies reveal that the inherent sensitivity and specificity of tip-enhanced Raman scattering (TERS) renders this technique a compelling method for fibril surface analysis at the single-particle level. Here, the reproducibility of TERS is demonstrated, indicating its relevance for detecting molecular variations. Consequently, individual fibrils are systematically investigated at nanometer spatial resolution. Spectral parameters were obtained by band-fitting, particularly focusing on the identification of the secondary structure via the amide III band and the differentiation of hydrophobic and hydrophilic domains on the surface. In addition multivariate data analysis, specifically the N-FINDR procedure, was employed to generate structure-specific maps. The ability of TERS to localize specific structural domains on fibril surfaces shows promise to the development of new fibril dissection strategies and can be generally applied to any (bio)chemical surface when structural variations at the nanometer level are of interest.
Spectroscopic methods with high spatial resolution are essential to understand the physical and chemical properties of nanoscale materials including biological and chemical materials. Tip-enhanced Raman spectroscopy (TERS) is a combination of surface-enhanced Raman spectroscopy (SERS) and scanning probe microscopy (SPM), which can provide high-resolution topographic and spectral information simultaneously below the diffraction limit of light. Even examples of sub-nanometer resolution have been demonstrated. This review intends to give an introduction to TERS, focusing on its basic principle and the experimental setup, the strengths followed by recent applications, developments, and perspectives in this field.
The
major structural components of protective mucus hydrogels on
mucosal surfaces are the secreted polymeric gel-forming mucins. The
very high molecular weight and extensive O-glycosylation of gel-forming
mucins, which are key to their viscoelastic properties, create problems
when studying mucins using conventional biochemical/structural techniques.
Thus, key structural information, such as the secondary structure
of the various mucin subdomains, and glycosylation patterns along
individual molecules, remains to be elucidated. Here, we utilized
Raman spectroscopy, Raman optical activity (ROA), circular dichroism
(CD), and tip-enhanced Raman spectroscopy (TERS) to study the structure
of the secreted polymeric gel-forming mucin MUC5B. ROA indicated that
the protein backbone of MUC5B is dominated by unordered conformation,
which was found to originate from the heavily glycosylated central
mucin domain by isolation of MUC5B O-glycan-rich regions. In sharp
contrast, recombinant proteins of the N-terminal region of MUC5B (D1-D2-D′-D3
domains, NT5B), C-terminal region of MUC5B (D4-B-C-CK domains, CT5B)
and the Cys-domain (within the central mucin domain of MUC5B) were
found to be dominated by the β-sheet. Using these findings,
we employed TERS, which combines the chemical specificity of Raman
spectroscopy with the spatial resolution of atomic force microscopy
to study the secondary structure along 90 nm of an individual MUC5B
molecule. Interestingly, the molecule was found to contain a large
amount of α-helix/unordered structures and many signatures of
glycosylation, pointing to a highly O-glycosylated region on the mucin.
Laser-produced solid density plasmas are well-known as table-top sources of electromagnetic radiation. Recent studies have shown that energetic broadband terahertz pulses (T rays) can also be generated from laser-driven compact ion accelerators. Here we report the measurement of record-breaking T-Ray pulses with energies no less than 0.7 mJ. The terahertz spectrum has been characterized for frequencies ranging from 0.1-133 THz. The dependence of T-Ray yield on incident laser energy is linear and shows no tendencies of saturation. The noncollinear emission pattern and the high yield reveal that the T rays are generated by the transient field at the rear surface of the solid target.
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