Subnanometer-resolved chemical imaging via multivariate analysis of tip-enhanced Raman maps

Song Jiang, Xianbiao Zhang, Yao Zhang, Chunrui Hu, Rui Zhang, Yang Zhang, Yuan Liao, Zachary J Smith, Zhenchao Dong, J G Hou

doi:10.1038/lsa.2017.98

Abstract:Tip-enhanced Raman spectroscopy (TERS) is a powerful surface analysis technique that can provide subnanometer-resolved images of nanostructures with site-specific chemical fingerprints. However, due to the limitation of weak Raman signals and the resultant difficulty in achieving TERS imaging with good signal-to-noise ratios (SNRs), the conventional single-peak analysis is unsuitable for distinguishing complex molecular architectures at the subnanometer scale. Here we demonstrate that the combination of subnanometer-resolved TERS imaging and advanced multivariate analysis can provide an unbiased panoramic view of the chemical identity and spatial distribution of different molecules on surfaces, yielding high-quality chemical images despite limited SNRs in individual pixel-level spectra. This methodology allows us to exploit the full power of TERS imaging and unambiguously distinguish between adjacent molecules with a resolution of ~0.4 nm, as well as to resolve submolecular features and the differences in molecular adsorption configurations. Our results provide a promising methodology that promotes TERS imaging as a routine analytical technique for the analysis of complex nanostructures on surfaces.

Two-color multiphoton in vivo imaging with a femtosecond diamond Raman laser

Evan P Perillo, Jeremy W Jarrett, Yen-Liang Liu, Ahmed Hassan, Daniel C Fernée, John R Goldak, Andrei Bonteanu, David J Spence, Hsin-Chih Yeh, Andrew K Dunn

doi:10.1038/lsa.2017.95

Abstract:Two-color multiphoton microscopy through wavelength mixing of synchronized lasers has been shown to increase the spectral window of excitable fluorophores without the need for wavelength tuning. However, most currently available dual output laser sources rely on the costly and complicated optical parametric generation approach. In this report, we detail a relatively simple and low cost diamond Raman laser pumped by a ytterbium fiber amplifier emitting at 1055 nm, which generates a first Stokes emission centered at 1240 nm with a pulse width of 100 fs. The two excitation wavelengths of 1055 and 1240 nm, along with the effective two-color excitation wavelength of 1140 nm, provide an almost complete coverage of fluorophores excitable within the range of 1000–1300 nm. When compared with 1055 nm excitation, two-color excitation at 1140 nm offers a 90% increase in signal for many far-red emitting fluorescent proteins (for example, tdKatushka2). We demonstrate multicolor imaging of tdKatushka2 and Hoechst 33342 via simultaneous two-color two-photon, and two-color three-photon microscopy in engineered 3D multicellular spheroids. We further discuss potential benefits and applications for two-color three-photon excitation. In addition, we show that this laser system is capable of in vivo imaging in mouse cortex to nearly 1 mm in depth with two-color excitation.

Super-resolution visible photoactivated atomic force microscopy

Seunghyun Lee, Owoong Kwon, Mansik Jeon, Jaejung Song, Seungjun Shin, HyeMi Kim, Minguk Jo, Taiuk Rim, Junsang Doh, Sungjee Kim, Junwoo Son, Yunseok Kim, Chulhong Kim

doi:10.1038/lsa.2017.80

Abstract:Imaging the intrinsic optical absorption properties of nanomaterials with optical microscopy (OM) is hindered by the optical diffraction limit and intrinsically poor sensitivity. Thus, expensive and destructive electron microscopy (EM) has been commonly used to examine the morphologies of nanostructures. Further, while nanoscale fluorescence OM has become crucial for investigating the morphologies and functions of intracellular specimens, this modality is not suitable for imaging optical absorption and requires the use of possibly undesirable exogenous fluorescent molecules for biological samples. Here we demonstrate super-resolution visible photoactivated atomic force microscopy (pAFM), which can sense intrinsic optical absorption with ~8 nm resolution. Thus, the resolution can be improved down to ~8 nm. This system can detect not only the first harmonic response, but also the higher harmonic response using the nonlinear effect. The thermoelastic effects induced by pulsed laser irradiation allow us to obtain visible pAFM images of single gold nanospheres, various nanowires, and biological cells, all with nanoscale resolution. Unlike expensive EM, the visible pAFM system can be simply implemented by adding an optical excitation sub-system to a commercial atomic force microscope.

Spin-manipulated nanoscopy for single nitrogen-vacancy center localizations in nanodiamonds

Martina Barbiero, Stefania Castelletto, Xiaosong Gan, Min Gu

doi:10.1038/lsa.2017.85

Abstract:Due to their exceptional optical and magnetic properties, negatively charged nitrogen-vacancy (NV) centers in nanodiamonds (NDs) have been identified as an indispensable tool for imaging, sensing and quantum bit manipulation. The investigation of the emission behaviors of single NV centers at the nanoscale is of paramount importance and underpins their use in applications ranging from quantum computation to super-resolution imaging. Here, we report on a spin-manipulated nanoscopy method for nanoscale resolutions of the collectively blinking NV centers confined within the diffraction-limited region. Using wide-field localization microscopy combined with nanoscale spin manipulation and the assistance of a microwave source tuned to the optically detected magnetic resonance (ODMR) frequency, we discovered that two collectively blinking NV centers can be resolved. Furthermore, when the collective emitters possess the same ground state spin transition frequency, the proposed method allows the resolving of each single NV center via an external magnetic field used to split the resonant dips. In spin manipulation, the three-level blinking dynamics provide the means to resolve two NV centers separated by distances of 23 nm. The method presented here offers a new platform for studying and imaging spin-related quantum interactions at the nanoscale with super-resolution techniques.

The fabrication of color-tunable organic light-emitting diode displays via solution processing

Fei Guo, Andre Karl, Qi-Fan Xue, Kai Cheong Tam, Karen Forberich, Christoph J Brabec

doi:10.1038/lsa.2017.94

Abstract:Electroluminescent devices based on organic semiconductors have attracted significant attention owing to their promising applications in flat-panel displays. The conventional display pixel consisting of side-by-side arrayed red, green and blue subpixels represents the mature technology but bears an intrinsic deficiency of a low pixel density. Constructing an individual color-tunable pixel that comprises vertically stacked subpixels is considered an advanced technology. Although color-tunable organic light-emitting diodes (OLEDs) have been fabricated using the vacuum deposition of small molecules, the solution processing of conjugated polymers would enable a much simpler and inexpensive manufacturing process. Here we present the all-solution processing of color-tunable OLEDs comprising two vertically stacked polymer emitters. A thin layer of highly conducting and transparent silver nanowires is introduced as the intermediate charge injection contact, which allows the emission spectrum and intensity of the tandem devices to be seamlessly manipulated. To demonstrate a viable application of this technology, a 4-by-4 pixelated matrix color-tunable display was fabricated.

Stable femtosecond X-rays with tunable polarization from a laser-driven accelerator

Andreas Döpp, Benoit Mahieu, Agustin Lifschitz, Cedric Thaury, Antoine Doche, Emilien Guillaume, Gabriele Grittani, Olle Lundh, Martin Hansson, Julien Gautier, Michaela Kozlova, Jean Philippe Goddet, Pascal Rousseau, Amar Tafzi, Victor Malka, Antoine Rousse, Sebastien Corde, Kim Ta Phuoc

doi:10.1038/lsa.2017.86

Abstract:Technology based on high-peak-power lasers has the potential to provide compact and intense radiation sources for a wide range of innovative applications. In particular, electrons that are accelerated in the wakefield of an intense laser pulse oscillate around the propagation axis and emit X-rays. This betatron source, which essentially reproduces the principle of a synchrotron at the millimeter scale, provides bright radiation with femtosecond duration and high spatial coherence. However, despite its unique features, the usability of the betatron source has been constrained by its poor control and stability. In this article, we demonstrate the reliable production of X-ray beams with tunable polarization. Using ionization-induced injection in a gas mixture, the orbits of the relativistic electrons emitting the radiation are reproducible and controlled. We observe that both the signal and beam profile fluctuations are significantly reduced and that the beam pointing varies by less than a tenth of the beam divergence. The polarization ratio reaches 80%, and the polarization axis can easily be rotated. We anticipate a broad impact of the source, as its unprecedented performance opens the way for new applications.

Nonlinear optical endomicroscopy for label-free functional histology in vivo

Wenxuan Liang, Gunnsteinn Hall, Bernhard Messerschmidt, Ming-Jun Li, Xingde Li

doi:10.1038/lsa.2017.82

Abstract:This manuscript reports on the first two-photon, label-free, metabolic imaging of biological tissues in vivo at histological resolution on an extremely compact, fiber-optic endomicroscopy platform. This system provides new opportunities for performing non-invasive and functional histological imaging of internal organs in vivo, in situ and in real time. As a routine clinical procedure, traditional histology has made significant impacts on medicine. However, the procedure is invasive and time consuming, suffers random sampling errors, and cannot provide in vivo functional information. The technology reported here features an extremely compact and flexible fiber-optic probe ~2 mm in diameter, enabling direct access to internal organs. Unprecedented two-photon imaging quality comparable to a large bench-top laser scanning microscope was achieved through technological innovations in double-clad fiber optics and miniature objective lenses (among many others). In addition to real-time label-free visualization of biological tissues in situ with subcellular histological detail, we demonstrated for the first time in vivo two-photon endomicroscopic metabolic imaging on a functioning mouse kidney model. Such breakthroughs in nonlinear endoscopic imaging capability present numerous promising opportunities for paradigm-shifting applications in both clinical diagnosis and basic research.

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