An electric field enhanced by a metallic nanoprobe has locally induced coherent anti-Stokes Raman scattering (CARS) of adenine molecules in a nanometric DNA network structure. Owing to the third-order nonlinearity, the excitation of the CARS polarization is extremely confined to the end of the tip apex, resulting in a spatial resolution far beyond the diffraction limit of light. Our tip-enhanced CARS microscope visualized the DNA network structure at a specific vibrational frequency (approximately 1337 cm(-1)) corresponding to the ring-breathing mode of diazole of adenine molecules.

No abstract

Kinesin-1, the founding member of the kinesin superfamily of proteins, is known to use only a subset of microtubules for transport in living cells. This biased use of microtubules is proposed as the guidance cue for polarized transport in neurons, but the underlying mechanisms are still poorly understood. Here, we report that kinesin-1 binding changes the microtubule lattice and promotes further kinesin-1 binding. This high-affinity state requires the binding of kinesin-1 in the nucleotide-free state. Microtubules return to the initial low-affinity state by washing out the binding kinesin-1 or by the binding of non-hydrolyzable ATP analogue AMPPNP to kinesin-1. X-ray fiber diffraction, fluorescence speckle microscopy, and second-harmonic generation microscopy, as well as cryo-EM, collectively demonstrated that the binding of nucleotide-free kinesin-1 to GDP microtubules changes the conformation of the GDP microtubule to a conformation resembling the GTP microtubule.

Tip-enhanced Raman scattering microscopy is a powerful technique for analysing nanomaterials at high spatial resolution far beyond the diffraction limit of light. However, imaging of intrinsic properties of materials such as individual molecules or local structures has not yet been achieved even with a tip-enhanced Raman scattering microscope. Here we demonstrate colour-coded tip-enhanced Raman scattering imaging of strain distribution along the length of a carbon nanotube. The strain is induced by dragging the nanotube with an atomic force microscope tip. A silver-coated nanotip is employed to enhance and detect Raman scattering from specific locations of the nanotube directly under the tip apex, representing deformation of its molecular alignment because of the existence of local strain. Our technique remarkably provides an insight into localized variations of structural properties in nanomaterials, which could prove useful for a variety of applications of carbon nanotubes and other nanomaterials as functional devices and materials.

We present a near-field Raman investigation in the subnanometric vicinity of a metallic nanotip, where the tip-sample distance is precisely controlled by our newly developed time-gated illumination technique. Using this scheme on an isolated carbon nanotube, we have profiled the spatial decay of evanescent light. We also investigated extremely short-ranged chemical and mechanical interactions between the metal on the tip apex and the molecules of an adenine sample, which are observable only within the subnanometric vicinity of the tip. The results show a near-field Raman investigation with an accuracy of better than a few angstroms. Further, this shows strong promise for superhigh resolution in optical microscopy based on this technique.

We report on the experimental identification of Raman modes that are enhanced through the chemical effect in surface enhanced Raman spectroscopy of 4-aminothiophenol (also known as p-mercaptoaniline) adsorbed on gold substrate. Introduction of a thin spacer layer between the metal and the sample can prevent any possible chemical bonding between metal atoms and sample molecules, hence such a sample shows only those Raman modes that are enhanced through the electromagnetic effect. Alternatively, a significant increase in the chemical effect could be observed in the presence of halide ions as compared to their absence. This result provides another way to experimentally identify those Raman modes that undergo chemical enhancement. In addition, apart from the electromagnetic-based resonance in SERS, chemical enhancement also shows a resonance with varying wavelength of the excitation light, which provides yet another way to experimentally identify chemically enhanced Raman modes in SERS. Some new chemically enhanced modes could be observed when the sample molecules were sandwiched between gold substrate and a gold nanotip. † Part of the "Martin Moskovits Festschrift".

To be able to predict antibiotic resistance in bacteria from fast label-free microscopic observations would benefit a broad range of applications in the biological and biomedical fields. Here, we demonstrate the utility of label-free Raman spectroscopy in monitoring the type of resistance and the mode of action of acquired resistance in a bacterial population of Escherichia coli, in the absence of antibiotics. Our findings are reproducible. Moreover, we identified spectral regions that best predicted the modes of action and explored whether the Raman signatures could be linked to the genetic basis of acquired resistance. Spectral peak intensities significantly correlated (False Discovery Rate, p < 0.05) with the gene expression of some genes contributing to antibiotic resistance genes. These results suggest that the acquisition of antibiotic resistance leads to broad metabolic effects reflected through Raman spectral signatures and gene expression changes, hinting at a possible relation between these two layers of complementary information.

System level understanding of the cell requires detailed description of the cell state, which is often characterized by the expression levels of proteins. However, understanding the cell state requires comprehensive information of the cell, which is usually obtained from a large number of cells and their disruption. In this study, we used Raman spectroscopy, which can report changes in the cell state without introducing any label, as a non-invasive method with single cell capability. Significant differences in Raman spectra were observed at the levels of both the cytosol and nucleus in different cell-lines from mouse, indicating that Raman spectra reflect differences in the cell state. Difference in cell state was observed before and after the induction of differentiation in neuroblastoma and adipocytes, showing that Raman spectra can detect subtle changes in the cell state. Cell state transitions during embryonic stem cell (ESC) differentiation were visualized when Raman spectroscopy was coupled with principal component analysis (PCA), which showed gradual transition in the cell states during differentiation. Detailed analysis showed that the diversity between cells are large in undifferentiated ESC and in mesenchymal stem cells compared with terminally differentiated cells, implying that the cell state in stem cells stochastically fluctuates during the self-renewal process. The present study strongly indicates that Raman spectral morphology, in combination with PCA, can be used to establish cells' fingerprints, which can be useful for distinguishing and identifying different cellular states.