Showing papers by "Satoshi Kawata published in 2013"

Raman and SERS microscopy for molecular imaging of live cells.

Abstract: Raman microscopy is a promising technology for visualizing the distribution of molecules in cells. A challenge for live-cell imaging using Raman microscopy has been long imaging times owing to the weak Raman signal. Here we present a protocol for constructing and using a Raman microscope equipped with both a slit-scanning excitation and detection system and a laser steering and nanoparticle-tracking system. Slit scanning allows Raman imaging with high temporal and spatial resolution, whereas the laser beam steering system enables dynamic surface-enhanced Raman imaging using gold nanoparticles. Both features enable mapping of the distributions of molecules in live cells and visualization of cellular transport pathways. Furthermore, its utility can be expanded to small-molecule imaging by using tiny Raman-active tags such as alkyne. For example, DNA synthesis in a cell can be visualized by detecting 5-ethynyl-2'-deoxyuridine (EdU), a deoxyuridine derivative with an alkyne moiety. We describe the optics, hardware and software to construct the Raman microscope, and discuss the conditions and parameters involved in live-cell imaging. The whole system can be built in ∼8 h.

Tip-enhanced nano-Raman analytical imaging of locally induced strain distribution in carbon nanotubes

Abstract: 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.

Tip-enhanced Raman investigation of extremely localized semiconductor-to-metal transition of a carbon nanotube.

Abstract: The electronic properties of single walled carbon nanotubes (SWNTs) can change with a slight deformation, such as the one caused by the pressure of one SWNT crossing over the other in an ``$X$'' shape. The effect, however, is extremely localized. We present a tip-enhanced Raman investigation of the extremely localized semiconductor-to-metal transition of SWNTs in such a situation, where we can see how the Fano interaction, which is a Raman signature of metallic behavior, grows towards the junction and is localized within a few nanometers of its vicinity. After exploring the deconvoluted components of the $G$-band Raman mode, we were able to reveal the change in electronic properties of a SWNT at extremely high spatial resolution along its length.

Plasmonics: Future Outlook

Abstract: Plasma resonance in metals exhibits some unique optical phenomena that occur on the surface of metal with nanostructures. The use of surface plasmons has been proposed in various fields, such as nanometer-resolution near-field optical microscopy, nanoscale optical circuits, single-molecule detection, molecular sensors, cancer treatment, solar cells, lasers, and holography. The study of plasma resonance is called "plasmonics" and is expected as a new field of nanophotonics. In this report, I review the principles and limits of plasmonics and give a future outlook.

Metal nanoparticles for nano-imaging and nano-analysis

Abstract: Metal nanoparticles have recently emerged as ubiquitous surface-enhanced Raman scattering (SERS) agents for nano-imaging and nano-analysis. These applications make use of the unique optical properties of metal nanoparticles to enhance the efficiency of Raman scattering, whereas the small size of the nanoparticles localizes the enhanced Raman scattering at the nanoscale. In this perspective, we review the recent progress in SERS nano-imaging and nano-spectroscopy using metal nanoparticles applied especially to biological samples and nanomaterials. For biosamples, the highly sensitive molecular SERS detection capability of metal nanoparticles is used to analyze intracellular molecules. For analysis of nanomaterials, an innovative approach called tip-enhanced Raman scattering (TERS) microscopy, where metal nanoparticles are used with an AFM cantilever, has proven to be extremely powerful for nano-imaging. The precise control and analysis of the interaction between the metal and the sample are thus the key to overcome the limitations of current microscopic and spectroscopic techniques, and to guide future developments.

Plasmonics for nanoimaging and nanospectroscopy.

Abstract: The science of surface plasmon polaritons, known as “plasmonics,” is reviewed from the viewpoint of applied spectroscopy. In this discussion, noble metals are regarded as reservoirs of photons exhibiting the functions of photon confinement and field enhancement at metallic nanostructures. The functions of surface plasmons are described in detail with an historical overview, and the applications of plasmonics to a variety of industry and sciences are shown. The slow light effect of surface plasmons is also discussed for nanoimaging capability of the near-field optical microscopy and tip-enhanced Raman microscopy. The future issues of plasmonics are also shown, including metamaterials and the extension to the ultraviolet and terahertz regions.

Far-field free tapping-mode tip-enhanced Raman microscopy

Abstract: A tip-enhanced Raman scattering (TERS) microscope has been developed, which is based on the tapping-mode operation of atomic force microscopy. By synchronizing a multichannel detector with tapping oscillation of the metallic nanotip, one can measure a tip-sample separation dependent TERS spectrum and dynamically obtain both near- and far-field Raman signals during the periodic oscillation of the tip. This facilitates TERS imaging with in situ point-by-point removal of far-field background, resulting in higher contrast in TERS imaging. Furthermore, we can obtain an extremely high spatial resolution of 8 nm. Also, tapping mode operation of tip has an added advantage of low sample damage, which could be important for future application of TERS to soft biological materials. Our TERS imaging technique enables us to construct far-field-free high-contrast near-field image at faster imaging speed with extremely high spatial resolution.

Plasmonically nanoconfined light probing invisible phonon modes in defect-free graphene.

Abstract: We present a simple plasmonic method that enables tuning of accessibility to the dipole-forbidden transition states of matter. This technique is realized by well-controlled plasmonic dimers, which can confine optical fields on the order of molecular dimensions. As an example, the approach is applied to activate invisible noncenter phonon modes of defect-free graphene in resonance Raman spectra. The relative intensity of the normally forbidden modes with respect to the dipole allowed modes progressively increases as the degree of field confinement increases. This opens up a novel avenue for both photochemical excitation of molecular systems and nanoscale characterization of materials.

Saturated excitation microscopy for sub-diffraction-limited imaging of cell clusters

Abstract: Saturated excitation (SAX) microscopy offers high-depth discrimination predominantly due to nonlinearity in the fluorescence response induced by the SAX. Calculation of the optical transfer functions and the edge responses for SAX microscopy revealed the contrast improvement of high-spatial frequency components in the sample structure and the effective reduction of background signals from the out-of-focus planes. Experimental observations of the edge response and x-z cross-sectional images of stained HeLa cells agreed well with theoretical investigations. We applied SAX microscopy to the imaging of three-dimensional cultured cell clusters and confirmed the resolution improvement at a depth of 40 μm. This study shows the potential of SAX microscopy for super-resolution imaging of deep parts of biological specimens.

Saturated excitation of fluorescent proteins for subdiffraction-limited imaging of living cells in three dimensions.

Abstract: We report, for the first time, the saturated excitation (SAX) of fluorescent proteins for subdiffraction-limited imaging of living cells in three-dimensions. To achieve saturation, a bright yellow and green fluorescent protein (Venus and EGFP) that exhibits a strong nonlinear fluorescence response to the high excitation intensity at the laser focus is used. Harmonic demodulation of the fluorescence signal produced by a modulated excitation light extracts the nonlinear fluorescence signals. After constructing the image from the nonlinear components, we obtain fluorescence images of living cells with spatial resolution beyond the diffraction limit. We also applied linear deconvolution to SAX microscopy and found it effective in further enhancing the contrast of small intracellular structures in the SAX image, confirming the expansion of the optical transfer function in SAX microscopy.

Stress redistribution in individual ultrathin strained silicon nanowires: a high-resolution polarized Raman study

Abstract: Strain nano-engineering provides valuable opportunities to create high-performance nanodevices by a precise tailoring of semiconductor band structure. Achieving these enhanced capabilities has sparked a surge of interest in controlling strain on the nanoscale. In this work, the stress behavior in ultrathin strained silicon nanowires directly on oxide is elucidated using background- free, high-resolution polarized Raman spectroscopy. We established a theoretical framework to quantify the stress from Raman shifts taking into account the anisotropy associated with the nanowire quasi-one-dimensional morphology. The investigated nanowires have lateral dimensions of 30, 50 and 80nm and a length of 1µm top-down fabricated by patterning and etching 15nm thick biaxially tensile strained silicon nanomembranes generated using heteroepitaxy

Color selectivity of surface-plasmon holograms illuminated with white light

Abstract: By using the optical frequency dependence of surface-plasmon polaritons, color images can be reconstructed from holograms illuminated with white light. We report details on the color selectivity of the color holograms. The selectivity is tuned by the thickness of a dielectric film covering a plasmonic metal film. When the dielectric is SiO2 and the metal is silver, the appropriate thicknesses are 25 and 55 nm, respectively. In terms of spatial color uniformity, holograms made of silver-film corrugations are better than holograms recorded on photographic film on a flat silver surface.

Two photon polymerization lithography for 3D microfabrication of single wall carbon nanotube/polymer composites

Abstract: Two photon polymerization (TPP) lithography has been established as a powerful tool to develop 3D fine structures of polymer materials, opening up a wide range applications such as micro-electromechanical systems (MEMS). TPP lithography is also promising for 3D micro fabrication of nanocomposites embedded with nanomaterials such as metal nanoparticles. Here, we make use of TPP lithography to fabricate 3D micro structural single wall carbon nanotube (SWCNT)/polymer composites. SWCNTs exhibit remarkable mechanical, electrical, thermal and optical properties, which leads to enhance performances of polymers by loading SWCNTs. SWCNTs were uniformly dispersed in an acrylate UV-curable monomer including a few amounts of photo-initiator and photo-sensitizer. A femtosecond pulsed laser emitting at 780 nm was focused onto the resin, resulting in the photo-polymerization of a nanometric volume of the resin through TPP. By scanning the focus spot three dimensionally, arbitrary 3D structures were created. The spatial resolution of the fabrication was sub-micrometer, and SWCNTs were embedded in the sub-micro sized structures. The fabrication technique enables one to fabricate 3D micro structural SWCNT/polymer composites into desired shapes, and thus the technique should open up the further applications of SWCNT/polymer composites such as micro sized photomechanical actuators.

Polarised Raman Imaging of Living Cells for Chemical Contrast Manipulation

Abstract: Raman spectral imaging has become a more and more popular technique in biological studies because it can extract chemical information from living cells in a label-free manner. One of the most challenging issues in the label-free Raman imaging of biological samples is to increase the molecular specificity in the spectra for better chemical contrast. Usually, the Raman spectrum from a cell is dominated by a few strong Raman bands such as the amide I band around 1650 cm -1 , CH 2 bend around 1445 cm -1 or the amide III band around 1300 cm -1 and it is not easy to get chemical contrast from other Raman bands that overlap with them. In this study, we aim to manipulate the chemical contrast in a living cell by exploiting the polarisation effects in Raman spectroscopy. By simply putting an analyser before the spectrometer, we can take the Raman image at the parallel and perpendicular polarisation against the incident light at the sample. The Raman spectra at the two orthogonal polarisations represent the Raman signals with different molecular orientation and symmetry of vibrations. Our experimental results demonstrate that at certain Raman shifts the two orthogonal polarisations indeed present different chemical contrasts. This indicates that polarized Raman imaging can help us visualise the different chemical contrasts that overlap at the same Raman shift and therefore increase the amount of chemical information we can get from cells.

Dynamic SERS imaging with gold nanoparticles transported in a living cell

Abstract: Surface enhanced Raman scattering (SERS) has been used to detect biological molecules at a low concentration. We developed a rapid Raman imaging system, which can image dynamic activity of SERS agents, such as gold nanoparticles, in a living cell and the temporal behaviors of SERS spectra. Combination of slit scanning and an EM-CCD camera for measuring SERS spectra enables us to obtain a SERS image in a few seconds. The system can also be used to track a single particle moving in a cell with a laser focus and measure SERS spectra with a temporal resolution of 50 msec. By using the developed microscope systems, we monitored the change of SERS spectra associated cell transportation functions.

Evaluation of localized semiconductor to metal transition of semiconducting carbon nanotube by Tip-enhanced Raman investigation

Abstract: Tailoring feature of single walled carbon nanotubes (SWNTs) in property by structure deformation has been an interdisciplinary subject of interest for researchers with an expectation that the control of the electronic property will open an access to new world where nano-circuit and nano-actuator exist and it is quit easy. Recently, drastic change of the properties of crossed SWNTs, for example by bridging them over other SWNTs [1], have received widespread attention because a transition from semiconducting state to metallic state was proved to appear only on the junction of crossed semiconducting SWNTs due to π* − σ* hybridization effect, which was theoretically expected since long before [2]. Here, we present a tip-enhanced Raman investigation of extremely localized transition from semiconducting to metal on the junction of crossed SWNTs.

Tip-enhanced Raman scattering study of metalized-semiconducting carbon nanotube

Abstract: We visualized that semiconducting single wall carbon nanotubes (SWCNTs) represent metallic property at a point where a few tubes crossed each other, by tip-enhanced Raman scattering (TERS) microscopy.

Saturable scattering and its application to superresolution microscopy

Abstract: Recently, several superresolution methods have been demonstrated to revolutionize the way we access the nano-world. However, these techniques are based on switching or saturation of fluorescence, and consequently are limited by switching reversibility and photobleaching. Here we show first superresolution far-field imaging based on scattering, which is a universal phenomenon without bleaching. Our principal finding is that scattering from plasmonics particles is saturable. By extracting the saturated part, sub-80-nm resolution is achieved. This work not only expands the horizon of superresolution imaging from fluorescence to scattering, but also points out the possibility of resolution enhancement for all imaging modalities that utilize plasmon properties.

Blur suppression of a holographic image with use of surface plasmons

Abstract: Holography is well-known technique of 3-dimensional imaging. A medium recorded the image is called hologram. To reconstruct objects, the holograms are illuminated with light waves. When fluorescent tubes or light emitting diode (LED) arrays illuminate holograms, reconstructed images are blurred, since a position of reconstructed image depend on illumination angle and angular-spreading light waves emitting from these plane light-sources reconstruct a series of the holographic images. Here we propose a blur suppression method of the holographic images by limiting incident-angle spreading of light waves by using surface plasmon polaritons (SPP) [1].

Surface enhanced Raman scattering (SERS) imaging of intracellular transportation in 3D

Abstract: We observed intracellular transportation by using surface-enhanced Raman scattering (SERS) from gold nanoparticles moving in cytosol. Simultaneous detection of the nanoparticle position and SERS spectra enables us to visualize micelles associated with the transportation process.