2018 Vol. 7, No. 6

Original Articles
Optical conductivity-based ultrasensitive mid-infrared biosensing on a hybrid metasurface
Yibo Zhu, Zhaoyi Li, Zhuang Hao, Christopher DiMarco, Panita Maturavongsadit, et al.
Published. 2018, 7(6) : 692-702 doi: 10.1038/s41377-018-0066-1
Optical devices are highly attractive for biosensing as they can not only enable quantitative measurements of analytes but also provide information on molecular structures. Unfortunately, typical refractive index-based optical sensors do not have sufficient sensitivity to probe the binding of low-molecular-weight analytes. Non-optical devices such as field-effect transistors can be more sensitive but do not offer some of the significant features of optical devices, particularly molecular fingerprinting. We present optical conductivity-based mid-infrared (mid-IR) biosensors that allow for sensitive and quantitative measurements of low-molecular-weight analytes as well as the enhancement of spectral fingerprints. The sensors employ a hybrid metasurface consisting of monolayer graphene and metallic nano-antennas and combine individual advantages of plasmonic, electronic and spectroscopic approaches. First, the hybrid metasurface sensors can optically detect target molecule-induced carrier doping to graphene, allowing highly sensitive detection of low-molecular-weight analytes despite their small sizes. Second, the resonance shifts caused by changes in graphene optical conductivity is a well-defined function of graphene carrier density, thereby allowing for quantification of the binding of molecules. Third, the sensor performance is highly stable and consistent thanks to its insensitivity to graphene carrier mobility degradation. Finally, the sensors can also act as substrates for surface-enhanced infrared spectroscopy. We demonstrated the measurement of monolayers of sub-nanometer-sized molecules or particles and affinity binding-based quantitative detection of glucose down to 200 pM (36 pg/mL). We also demonstrated enhanced fingerprinting of minute quantities of glucose and polymer molecules.
Plasmonic bacteria on a nanoporous mirror via hydrodynamic trapping for rapid identification of waterborne pathogens
Keumrai Whang, Jong-Hwan Lee, Yonghee Shin, Wooju Lee, Young Wan Kim, et al.
Published. 2018, 7(6) : 716-724 doi: 10.1038/s41377-018-0071-4
A rapid, precise method for identifying waterborne pathogens is critically needed for effective disinfection and better treatment. However, conventional methods, such as culture-based counting, generally suffer from slow detection times and low sensitivities. Here, we developed a rapid detection method for tracing waterborne pathogens by an innovative optofluidic platform, a plasmonic bacteria on a nanoporous mirror, that allows effective hydrodynamic cell trapping, enrichment of pathogens, and optical signal amplifications. We designed and simulated the integrated optofluidic platform to maximize the enrichment of the bacteria and to align bacteria on the nanopores and plasmonic mirror via hydrodynamic cell trapping. Gold nanoparticles are self-assembled to form antenna arrays on the surface of bacteria, such as Escherichia coli and Pseudomonas aeruginosa, by replacing citrate with hydroxylamine hydrochloride in order to amplify the signal of the plasmonic optical array. Owing to the synergistic contributions of focused light via the nanopore geometry, self-assembled nanoplasmonic optical antennas on the surface of bacteria, and plasmonic mirror, we obtain a sensitivity of detecting E. coli as low as 102 cells/ml via surface-enhanced Raman spectroscopy. We believe that our label-free strategy via an integrated optofluidic platform will pave the way for the rapid, precise identification of various pathogens.
Multimode optical fiber transmission with a deep learning network
Babak Rahmani, Damien Loterie, Georgia Konstantinou, Demetri Psaltis, Christophe Moser
Published. 2018, 7(6) : 738-748 doi: 10.1038/s41377-018-0074-1
Multimode fibers (MMFs) are an example of a highly scattering medium, which scramble the coherent light propagating within them to produce seemingly random patterns. Thus, for applications such as imaging and image projection through an MMF, careful measurements of the relationship between the inputs and outputs of the fiber are required. We show, as a proof of concept, that a deep neural network can learn the input-output relationship in a 0.75 m long MMF. Specifically, we demonstrate that a deep convolutional neural network (CNN) can learn the nonlinear relationships between the amplitude of the speckle pattern (phase information lost) obtained at the output of the fiber and the phase or the amplitude at the input of the fiber. Effectively, the network performs a nonlinear inversion task. We obtained image fidelities (correlations) as high as ~98% for reconstruction and ~94% for image projection in the MMF compared with the image recovered using the full knowledge of the system transmission characterized with the complex measured matrix. We further show that the network can be trained for transfer learning, i.e., it can transmit images through the MMF, which belongs to another class not used for training/testing.
Attenuation artifacts in light sheet fluorescence microscopy corrected by OPTiSPIM
Jürgen Mayer, Alexandre Robert-Moreno, James Sharpe, Jim Swoger
Published. 2018, 7(6) : 703-715 doi: 10.1038/s41377-018-0068-z
Light sheet fluorescence microscopy (LSFM) is rapidly becoming an essential technology for mesoscopic imaging of samples such as embryos and adult mouse organs. However, LSFM can suffer from optical artifacts for which there is no intrinsic solution. The attenuation of light due to absorbing material causes "shadow" artifacts along both the illumination and detection paths. Several approaches have been introduced to reduce this problem, including scanning illumination and multi-view imaging. However, neither of these approaches completely eliminates the problem. If the distribution of the absorbing material is complex, shadows cannot be avoided. We introduce a new approach that relies on multi-modal integration of two very different mesoscopic techniques. Unlike LSFM, optical projection tomography (OPT) can operate in transmission mode to create a voxel map of the 3D distribution of the sample's optical attenuation. Here, we demonstrate a hybrid instrument (OPTiSPIM) that can quantify this attenuation and use the information to correct the shadow artifacts of LSFM.
GOBO projection for 3D measurements at highest frame rates: a performance analysis
Stefan Heist, Patrick Dietrich, Martin Landmann, Peter Kühmstedt, Gunther Notni, et al.
Published. 2018, 7(6) : 725-737 doi: 10.1038/s41377-018-0072-3
Aperiodic sinusoidal patterns that are cast by a GOBO (GOes Before Optics) projector are a powerful tool for optically measuring the surface topography of moving or deforming objects with very high speed and accuracy. We optimised the first experimental setup that we were able to measure inflating car airbags at frame rates of more than 50kHz while achieving a 3D point standard deviation of ~500µm. Here, we theoretically investigate the method of GOBO projection of aperiodic sinusoidal fringes. In a simulation-based performance analysis, we examine the parameters that influence the accuracy of the measurement result and identify an optimal pattern design that yields the highest measurement accuracy. We compare the results with those that were obtained via GOBO projection of phase-shifted sinusoidal fringes. Finally, we experimentally verify the theoretical findings. We show that the proposed technique has several advantages over conventional fringe projection techniques, as the easy-to-build and cost-effective GOBO projector can provide a high radiant flux, allows high frame rates, and can be used over a wide spectral range.
Photonic waveguide to free-space Gaussian beam extreme mode converter
Sangsik Kim, Daron A. Westly, Brian J. Roxworthy, Qing Li, Alexander Yulaev, et al.
Published. 2018, 7(6) : 767-779 doi: 10.1038/s41377-018-0073-2
Integration of photonic chips with millimeter-scale atomic, micromechanical, chemical, and biological systems can advance science and enable new miniaturized hybrid devices and technology. Optical interaction via small evanescent volumes restricts performance in applications such as gas spectroscopy, and a general ability to photonically access optical fields in large free-space volumes is desired. However, conventional inverse tapers and grating couplers do not directly scale to create wide, high-quality collimated beams for low-loss diffraction-free propagation over many millimeters in free space, necessitating additional bulky collimating optics and expensive alignment. Here, we develop an extreme mode converter, which is a compact planar photonic structure that efficiently couples a 300 nm × 250 nm silicon nitride high-index single-mode waveguide to a well-collimated near surface-normal Gaussian beam with an ≈160 µm waist, which corresponds to an increase in the modal area by a factor of > 105. The beam quality is thoroughly characterized, and propagation over 4 mm in free space and coupling back into a single-mode photonic waveguide with low loss via a separate identical mode converter is demonstrated. To achieve low phase error over a beam area that is > 100× larger than that of a typical grating coupler, our approach separates the two-dimensional mode expansion into two sequential separately optimized stages, which create a fully expanded and well-collimated Gaussian slab mode before out-coupling it into free space. Developed at 780 nm for integration with chip-scale atomic vapor cell cavities, our design can be adapted for visible, telecommunication, or other wavelengths. The technique can be expanded to more arbitrary phase and intensity control of both large-diameter, free-space optical beams and wide photonic slab modes.
Substructure imaging of heterogeneous nanomaterials with enhanced refractive index contrast by using a functionalized tip in photoinduced force microscopy
Junghoon Jahng, Heejae Yang, Eun Seong Lee
Published. 2018, 7(6) : 749-757 doi: 10.1038/s41377-018-0069-y
The opto-mechanical force response from light-illuminated nanoscale materials has been exploited in many tip-based imaging applications to characterize various heterogeneous nanostructures. Such a force can have two origins: thermal expansion and induced dipoles. The thermal expansion reflects the absorption of the material, which enables one to chemically characterize a material at the absorption resonance. The induced dipole interaction reflects the local refractive indices of the material underneath the tip, which is useful to characterize a material in the spectral region where no absorption resonance occurs, as in the infrared (IR)-inactive region. Unfortunately, the dipole force is relatively small, and the contrast is rarely discernible for most organic materials and biomaterials, which only show a small difference in refractive indices for their components. In this letter, we demonstrate that refractive index contrast can be greatly enhanced with the assistance of a functionalized tip. With the enhanced contrast, we can visualize the substructure of heterogeneous biomaterials, such as a polyacrylonitrile-nanocrystalline cellulose (PAN-NCC) nanofiber. From substructural visualization, we address the issue of the tensile strength of PAN-NCC fibers fabricated by several different mixing methods. Our understanding from the present study will open up a new opportunity to provide enhanced sensitivity for substructure mapping of nanobiomaterials, as well as local field mapping of photonic devices, such as surface polaritons on semiconductors, metals and van der Waals materials.
All-optical forward-viewing photoacoustic probe for high-resolution 3D endoscopy
Rehman Ansari, Edward Z. Zhang, Adrien E. Desjardins, Paul C. Beard
Published. 2018, 7(6) : 758-766 doi: 10.1038/s41377-018-0070-5
A miniature forward-viewing endoscopic probe that provides high-resolution 3D photoacoustic images is demonstrated. The probe is of outer diameter 3.2 mm and comprised of a transparent Fabry-Pérot (FP) polymer-film ultrasound sensor that is located at the distal end of a rigid optical fiber bundle. Excitation laser pulses are coupled simultaneously into all cores of the bundle and are transmitted through the FP sensor to provide wide-field tissue illumination at the distal end. The resulting photoacoustic waves are mapped in 2D by sequentially scanning the input end of the bundle with an interrogation laser beam in order to individually address different points on the FP sensor. In this way, the sensor acts as a high-density ultrasound array that is comprised of 50, 000 individual elements, each of which is 12 µm in diameter, within the 3.2 mm diameter footprint of the probe. The fine spatial sampling that this affords, along with the wide bandwidth (f-3dB = 34 MHz) of the sensor, enables a high-resolution photoacoustic image to be reconstructed. The measured on-axis lateral resolution of the probe was depth-dependent and ranged from 45-170 µm for depths between 1 and 7 mm, and the vertical resolution was 31 µm over the same depth range. The system was evaluated by acquiring 3D images of absorbing phantoms and the microvascular anatomies of a duck embryo and mouse skin. Excellent image fidelity was demonstrated. It is anticipated that this type of probe could find application as a tool for guiding laparoscopic procedures, fetal surgery and other minimally invasive interventions that require a millimeter-scale forward-viewing 3D photoacoustic imaging probe.
Ultrafast cryptography with indefinitely switchable optical nanoantennas
Pujuan Ma, Lei Gao, Pavel Ginzburg, Roman E. Noskov
Published. 2018, 7(6) : 788-796 doi: 10.1038/s41377-018-0079-9
Bistability is widely exploited to demonstrate all-optical signal processing and light-based computing. The standard paradigm of switching between two steady states corresponding to "0" and "1" bits is based on the rule that a transition occurs when the signal pulse intensity overcomes the bistability threshold, and otherwise, the system remains in the initial state. Here, we break with this concept by revealing the phenomenon of indefinite switching in which the eventual steady state of a resonant bistable system is transformed into a nontrivial function of signal pulse parameters for moderately intense signal pulses. The essential nonlinearity of the indefinite switching allows realization of well-protected cryptographic algorithms with a single bistable element in contrast to software-assisted cryptographic protocols that require thousands of logic gates. As a proof of concept, we demonstrate stream deciphering of the word "enigma" by means of an indefinitely switchable optical nanoantenna. An extremely high bitrate ranging from ~0.1 to 1 terabits per second and a small size make such systems promising as basic elements for all-optical cryptographic architectures.
Facile metagrating holograms with broadband and extreme angle tolerance
Zi-Lan Deng, Junhong Deng, Xin Zhuang, Shuai Wang, Tan Shi, et al.
Published. 2018, 7(6) : 780-787 doi: 10.1038/s41377-018-0075-0
The emerging meta-holograms rely on arrays of intractable meta-atoms with various geometries and sizes for customized phase profiles that can precisely modulate the phase of a wavefront at an optimal incident angle for given wavelengths. The stringent and band-limited angle tolerance remains a fundamental obstacle for their practical application, in addition to high fabrication precision demands. Utilizing a different design principle, we determined that facile metagrating holograms based on extraordinary optical diffraction can allow the molding of arbitrary wavefronts with extreme angle tolerances (near-grazing incidence) in the visible–near-infrared regime. By modulating the displacements between uniformly sized meta-atoms rather than the geometrical parameters, the metagratings produce a robust detour phase profile that is irrespective of the wavelength or incident angle. The demonstration of high-fidelity meta-holograms and in-site polarization multiplexing significantly simplifies the metasurface design and lowers the fabrication demand, thereby opening new routes for flat optics with high performances and improved practicality.
Optical prediction of single muscle fiber force production using a combined biomechatronics and second harmonic generation imaging approach
Dominik Schneidereit, Stefanie Nübler, Gerhard Prölß, Barbara Reischl, Sebastian Schürmann, et al.
Published. 2018, 7(6) : 797-810 doi: 10.1038/s41377-018-0080-3
Skeletal muscle is an archetypal organ whose structure is tuned to match function. The magnitude of order in muscle fibers and myofibrils containing motor protein polymers determines the directed force output of the summed force vectors and, therefore, the muscle's power performance on the structural level. Structure and function can change dramatically during disease states involving chronic remodeling. Cellular remodeling of the cytoarchitecture has been pursued using noninvasive and label-free multiphoton second harmonic generation (SHG) microscopy. Hereby, structure parameters can be extracted as a measure of myofibrillar order and thus are suggestive of the force output that a remodeled structure can still achieve. However, to date, the parameters have only been an indirect measure, and a precise calibration of optical SHG assessment for an exerted force has been elusive as no technology in existence correlates these factors. We engineered a novel, automated, high-precision biomechatronics system into a multiphoton microscope allows simultaneous isometric Ca2+-graded force or passive viscoelasticity measurements and SHG recordings. Using this MechaMorph system, we studied force and SHG in single EDL muscle fibers from wt and mdx mice; the latter serves as a model for compromised force and abnormal myofibrillar structure. We present Ca2+-graded isometric force, pCa-force curves, passive viscoelastic parameters and 3D structure in the same fiber for the first time. Furthermore, we provide a direct calibration of isometric force to morphology, which allows noninvasive prediction of the force output of single fibers from only multiphoton images, suggesting a potential application in the diagnosis of myopathies.
Near-resonance enhanced label-free stimulated Raman scattering microscopy with spatial resolution near 130 nm
Yali Bi, Chi Yang, Yage Chen, Shuai Yan, Guang Yang, et al.
Published. 2018, 7(6) : 811-820 doi: 10.1038/s41377-018-0082-1
High-resolution optical microscopes that can break 180 nm in spatial resolution set to conventional microscopies are much-needed tools. However, current optical microscopes have to rely on exogenous fluorescent labels to achieve high resolution in biological imaging. Herein, we report near-resonance enhanced label-free stimulated Raman scattering (SRS) microscopy with a lateral resolution near 130 nm, in which the high-resolution image contrast originates directly from a low concentration of endogenous biomolecules, with sensitivity gains of approximately 23 times. Moreover, by using a 0.3-m-long optical fiber, we developed hyperspectral SRS microscopy based on spectral focusing technology. Attributed to enhancements in spatial resolution and sensitivity, we demonstrated high-resolution imaging of three-dimensional structures in single cells and high-resolution mapping of large-scale intact mouse brain tissues in situ. By using enhanced high-resolution hyperspectral SRS, we chemically observed sphingomyelin distributed in the myelin sheath that insulates single axons. Our concept opens the door to biomedical imaging with ~130 nm resolution.
Edge-emitting polariton laser and amplifier based on a ZnO waveguide
O. Jamadi, F. Reveret, P. Disseix, F. Medard, J. Leymarie, et al.
Published. 2018, 7(6) : 828-835 doi: 10.1038/s41377-018-0084-z
We demonstrate edge-emitting exciton-polariton (polariton) laser operation from 5 to 300 K and polariton amplifiers based on polariton modes within ZnO waveguides. The guided mode dispersion below and above the lasing threshold is directly measured using gratings placed on top of the sample, fully demonstrating the polaritonic nature of the lasing modes. The threshold is found to be smaller than that expected for radiative polaritons in planar ZnO microcavities below 150 K and comparable above. These results open up broad perspectives for guided polaritonics by enabling easier and more straightforward implementation of polariton integrated circuits that exploit fast propagating polaritons, and, possibly, topological protection.
Full-duplex light communication with a monolithic multicomponent system
Yongjin Wang, Xin Wang, Bingcheng Zhu, Zheng Shi, Jialei Yuan, et al.
Published. 2018, 7(6) : 821-827 doi: 10.1038/s41377-018-0083-0
A monolithic multicomponent system is proposed and implemented on a Ⅲ-nitride-on-silicon platform, whereby two multiple-quantum-well diodes (MQW-diodes) are interconnected by a suspended waveguide. Both MQW-diodes have an identical low-In-content InGaN/Al0.10Ga0.90N MQW structure and are produced by the same fabrication process flow. When appropriately biased, both MQW-diodes operate under a simultaneous emission-detection mode and function as a transmitter and a receiver at the same time, forming an in-plane full-duplex light communication system. Real-time full-duplex audio communication is experimentally demonstrated using the monolithic multicomponent system in combination with an external circuit.
Spin-controlled wavefront shaping with plasmonic chiral geometric metasurfaces
Yang Chen, Xiaodong Yang, Jie Gao
Published. 2018, 7(6) : 836-845 doi: 10.1038/s41377-018-0086-x
Metasurfaces, as a two-dimensional (2D) version of metamaterials, have drawn considerable attention for their revolutionary capability in manipulating the amplitude, phase, and polarization of light. As one of the most important types of metasurfaces, geometric metasurfaces provide a versatile platform for controlling optical phase distributions due to the geometric nature of the generated phase profile. However, it remains a great challenge to design geometric metasurfaces for realizing spin-switchable functionalities because the generated phase profile with the converted spin is reversed once the handedness of the incident beam is switched. Here, we propose and experimentally demonstrate chiral geometric metasurfaces based on intrinsically chiral plasmonic stepped nanoapertures with a simultaneously high circular dichroism in transmission (CDT) and large cross-polarization ratio (CPR) in transmitted light to exhibit spin-controlled wavefront shaping capabilities. The chiral geometric metasurfaces are constructed by merging two independently designed subarrays of the two enantiomers for the stepped nanoaperture. Under a certain incident handedness, the transmission from one subarray is allowed, while the transmission from the other subarray is strongly prohibited. The merged metasurface then only exhibits the transmitted signal with the phase profile of one subarray, which can be switched by changing the incident handedness. Based on the chiral geometric metasurface, both chiral metasurface holograms and the spin-dependent generation of hybrid-order Poincaré sphere beams are experimentally realized. Our approach promises further applications in spin-controlled metasurface devices for complex beam conversion, image processing, optical trapping, and optical communications.
Broadband achromatic dielectric metalenses
Sajan Shrestha, Adam C. Overvig, Ming Lu, Aaron Stein, Nanfang Yu
Published. 2018, 7(6) : 846-856 doi: 10.1038/s41377-018-0078-x
Metasurfaces offer a unique platform to precisely control optical wavefronts and enable the realization of flat lenses, or metalenses, which have the potential to substantially reduce the size and complexity of imaging systems and to realize new imaging modalities. However, it is a major challenge to create achromatic metalenses that produce a single focal length over a broad wavelength range because of the difficulty in simultaneously engineering phase profiles at distinct wavelengths on a single metasurface. For practical applications, there is a further challenge to create broadband achromatic metalenses that work in the transmission mode for incident light waves with any arbitrary polarization state. We developed a design methodology and created libraries of meta-units—building blocks of metasurfaces—with complex cross-sectional geometries to provide diverse phase dispersions (phase as a function of wavelength), which is crucial for creating broadband achromatic metalenses. We elucidated the fundamental limitations of achromatic metalens performance by deriving mathematical equations that govern the tradeoffs between phase dispersion and achievable lens parameters, including the lens diameter, numerical aperture (NA), and bandwidth of achromatic operation. We experimentally demonstrated several dielectric achromatic metalenses reaching the fundamental limitations. These metalenses work in the transmission mode with polarization-independent focusing efficiencies up to 50% and continuously provide a near-constant focal length over λ = 1200–1650 nm. These unprecedented properties represent a major advance compared to the state of the art and a major step toward practical implementations of metalenses.
Doped, conductive SiO2 nanoparticles for large microwave absorption
Michael Green, Zhanqiang Liu, Peng Xiang, Yan Liu, Minjie Zhou, et al.
Published. 2018, 7(6) : 857-865 doi: 10.1038/s41377-018-0088-8
Although many materials have been studied for the purpose of microwave absorption, SiO2 has never been reported as a good candidate. In this study, we present for the first time that doped, microwave conductive SiO2 nanoparticles can possess an excellent microwave absorbing performance. A large microwave reflection loss (RL) of −55.09 dB can be obtained. The large microwave absorption originates mainly from electrical relaxation rather than the magnetic relaxation of the incoming microwave field. The electrical relaxation is attributed to a large electrical conductivity that is enabled by the incorporation of heterogeneous (N, C and Cl) atoms. The removal of the magnetic susceptibility only results in a negligible influence of the microwave absorption. In contrast, the removal of the heterogeneous atoms leads to a large decrease in the electrical conductivity and microwave absorption performance. Meanwhile, the microwave absorption characteristics can be largely adjusted with a change of the thickness, which provides large flexibility for various microwave absorption applications.
X-ray-activated long persistent phosphors featuring strong UVC afterglow emissions
Yan-Min Yang, Zhi-Yong Li, Jun-Ying Zhang, Yue Lu, Shao-Qiang Guo, et al.
Published. 2018, 7(6) : 866-876 doi: 10.1038/s41377-018-0089-7
Phosphors emitting visible and near-infrared persistent luminescence have been explored extensively owing to their unusual properties and commercial interest in their applications such as glow-in-the-dark paints, optical information storage, and in vivo bioimaging. However, no persistent phosphor that features emissions in the ultraviolet C range (200-280 nm) has been known to exist so far. Here, we demonstrate a strategy for creating a new generation of persistent phosphor that exhibits strong ultraviolet C emission with an initial power density over 10 milliwatts per square meter and an afterglow of more than 2 h. Experimental characterizations coupled with first-principles calculations have revealed that structural defects associated with oxygen introduction-induced anion vacancies in fluoride elpasolite can function as electron traps, which capture and store a large number of electrons triggered by X-ray irradiation. Notably, we show that the ultraviolet C afterglow intensity of the yielded phosphor is sufficiently strong for sterilization. Our discovery of this ultraviolet C afterglow opens up new avenues for research on persistent phosphors, and it offers new perspectives on their applications in terms of sterilization, disinfection, drug release, cancer treatment, anti-counterfeiting, and beyond.
Independent control of harmonic amplitudes and phases via a time-domain digital coding metasurface
Jun Yan Dai, Jie Zhao, Qiang Cheng, Tie Jun Cui
Published. 2018, 7(6) : 888-897 doi: 10.1038/s41377-018-0092-z
Harmonic manipulations are important for applications such as wireless communications, radar detection and biological monitoring. A general approach to tailor the harmonics involves the use of additional amplifiers and phase shifters for the precise control of harmonic amplitudes and phases after the mixing process; however, this approach leads to issues of high cost and system integration. Metasurfaces composed of a periodic array of subwavelength resonators provide additional degrees of freedom to realize customized responses to incident light and highlight the possibility for nonlinear control by taking advantage of time-domain properties. Here, we designed and experimentally characterized a reflective time-domain digital coding metasurface, with independent control of the harmonic amplitude and phase. As the reflection coefficient is dynamically modulated in a predefined way, a large conversion rate is observed from the carrier signal to the harmonic components, with magnitudes and phases that can be accurately and separately engineered. In addition, by encoding the reflection phases of the meta-atoms, beam scanning for multiple harmonics can be implemented via different digital coding sequences, thus removing the need for intricate phase-shift networks. This work paves the way for efficient harmonic control for applications in communications, radar, and related areas.
In vivo theranostics with near-infrared-emitting carbon dots-highly efficient photothermal therapy based on passive targeting after intravenous administration
Xin Bao, Ye Yuan, Jingqin Chen, Bohan Zhang, Di Li, et al.
Published. 2018, 7(6) : 877-887 doi: 10.1038/s41377-018-0090-1
Carbon dots that exhibit near-infrared fluorescence (NIR CDs) are considered emerging nanomaterials for advanced biomedical applications with low toxicity and superior photostability and targeting compared to currently used photoluminescence agents. Despite progress in the synthesis of NIR CDs, there remains a key obstacle to using them as an in vivo theranostic agent. This work demonstrates that the newly developed sulfur and nitrogen codoped NIR CDs are highly efficient in photothermal therapy (PTT) in mouse models (conversion efficiency of 59%) and can be readily visualized by photoluminescence and photoacoustic imaging. The real theranostic potential of NIR CDs is enhanced by their unique biodistribution and targeting. Contrary to all other nanomaterials that have been tested in biomedicine, they are excreted through the body's renal filtration system. Moreover, after intravenous injection, NIR CDs are accumulated in tumor tissue via passive targeting, without any active species such as antibodies. Due to their accumulation in tumor tissue without the need for intratumor injection, high photothermal conversion, excellent optical and photoacoustic imaging performance, and renal excretion, the developed CDs are suitable for transfer to clinical biomedical practice.
Covert infrared image encoding through imprinted plasmonic cavities
Daniel Franklin, Sushrut Modak, Abraham Vázquez-Guardado, Alireza Safaei, Debashis Chanda
Published. 2018, 7(6) : 898-905 doi: 10.1038/s41377-018-0095-9
Functional surfaces that can control light across the electromagnetic spectrum are highly desirable. Plasmonic nanostructures can assume this role by exhibiting dimension-tunable resonances that span multiple electromagnetic regimes. However, changing these structural parameters often impacts the higher-order resonances and spectral features in lower-wavelength domains. In this study, we discuss a cavity-coupled plasmonic system with resonances that are tunable across the 3-5 or 8-14 μm infrared bands while retaining near-invariant spectral properties in the visible domain. This result is accomplished by regime-dependent resonance mechanisms and their dependence on independent structural parameters. Through the identification and constraint of key parameters, we demonstrate multispectral data encoding, where images, viewable in the infrared spectral domain, appear as uniform areas of color in the visible domain-effectively hiding the information. Fabricated by large area nanoimprint lithography and compatible with flexible surfaces, the proposed system can produce multifunctional coatings for thermal management, camouflage, and anti-counterfeiting.
Watt-scale super-octave mid-infrared intrapulse difference frequency generation
Christian Gaida, Martin Gebhardt, Tobias Heuermann, Fabian Stutzki, Cesar Jauregui, et al.
Published. 2018, 7(6) : 925-932 doi: 10.1038/s41377-018-0099-5
The development of high-power, broadband sources of coherent mid-infrared radiation is currently the subject of intense research that is driven by a substantial number of existing and continuously emerging applications in medical diagnostics, spectroscopy, microscopy, and fundamental science. One of the major, long-standing challenges in improving the performance of these applications has been the construction of compact, broadband mid-infrared radiation sources, which unify the properties of high brightness and spatial and temporal coherence. Due to the lack of such radiation sources, several emerging applications can be addressed only with infrared (IR)-beamlines in large-scale synchrotron facilities, which are limited regarding user access and only partially fulfill these properties. Here, we present a table-top, broadband, coherent mid-infrared light source that provides brightness at an unprecedented level that supersedes that of synchrotrons in the wavelength range between 3.7 and 18 µm by several orders of magnitude. This result is enabled by a high-power, few-cycle Tm-doped fiber laser system, which is employed as a pump at 1.9 µm wavelength for intrapulse difference frequency generation (IPDFG). IPDFG intrinsically ensures the formation of carrier-envelope-phase stable pulses, which provide ideal prerequisites for state-of-the-art spectroscopy and microscopy.
Multichannel vectorial holographic display and encryption
Ruizhe Zhao, Basudeb Sain, Qunshuo Wei, Chengchun Tang, Xiaowei Li, et al.
Published. 2018, 7(6) : 906-914 doi: 10.1038/s41377-018-0091-0
Since its invention, holography has emerged as a powerful tool to fully reconstruct the wavefronts of light including all the fundamental properties (amplitude, phase, polarization, wave vector, and frequency). For exploring the full capability for information storage/display and enhancing the encryption security of metasurface holograms, smart multiplexing techniques together with suitable metasurface designs are highly demanded. Here, we integrate multiple polarization manipulation channels for various spatial phase profiles into a single birefringent vectorial hologram by completely avoiding unwanted cross-talk. Multiple independent target phase profiles with quantified phase relations that can process significantly different information in different polarization states are realized within a single metasurface. For our metasurface holograms, we demonstrate high fidelity, large efficiency, broadband operation, and a total of twelve polarization channels. Such multichannel polarization multiplexing can be used for dynamic vectorial holographic display and can provide triple protection for optical security. The concept is appealing for applications of arbitrary spin to angular momentum conversion and various phase modulation/beam shaping elements.
A stoichiometric terbium-europium dyad molecular thermometer: energy transfer properties
Guochen Bao, Ka-Leung Wong, Dayong Jin, Peter A. Tanner
Published. 2018, 7(6) : 915-924 doi: 10.1038/s41377-018-0097-7
The optical thermometer has shown great promise for use in the fields of aeronautical engineering, environmental monitoring and medical diagnosis. Self-referencing lanthanide thermo-probes distinguish themselves because of their accuracy, calibration, photostability, and temporal dimension of signal. However, the use of conventional lanthanide-doped materials is limited by their poor reproducibility, random distance between energy transfer pairs and interference by energy migration, thereby restricting their utility. Herein, a strategy for synthesizing hetero-dinuclear complexes that comprise chemically similar lanthanides is introduced in which a pair of thermosensitive dinuclear complexes, cycTb-phEu and cycEu-phTb, were synthesized. Their structures were geometrically optimized with an internuclear distance of approximately 10.6Å. The sensitive linear temperature-dependent luminescent intensity ratios of europium and terbium emission over a wide temperature range (50-298K and 10-200K, respectively) and their temporal dimension responses indicate that both dinuclear complexes can act as excellent self-referencing thermometers. The energy transfer from Tb3+ to Eu3+ is thermally activated, with the most important pathway involving the 7F1 Eu3+ J-multiplet at room temperature. The energy transfer from the antenna to Eu3+ was simulated, and it was found that the most important ligand contributions to the rate come from transfers to the Eu3+ upper states rather than direct ligand-metal transfer to 5D1 or 5D0. As the first molecular-based thermometer with clear validation of the metal ratio and a fixed distance between the metal pairs, these dinuclear complexes can be used as new materials for temperature sensing and can provide a new platform for understanding the energy transfer between lanthanide ions.
Macroscale fluorescence imaging against autofluorescence under ambient light
Ruikang Zhang, Raja Chouket, Marie-Aude Plamont, Zsolt Kelemen, Agathe Espagne, et al.
Published. 2018, 7(6) : 933-944 doi: 10.1038/s41377-018-0098-6
Macroscale fluorescence imaging is increasingly used to observe biological samples. However, it may suffer from spectral interferences that originate from ambient light or autofluorescence of the sample or its support. In this manuscript, we built a simple and inexpensive fluorescence macroscope, which has been used to evaluate the performance of Speed OPIOM (Out of Phase Imaging after Optical Modulation), which is a reference-free dynamic contrast protocol, to selectively image reversibly photoswitchable fluorophores as labels against detrimental autofluorescence and ambient light. By tuning the intensity and radial frequency of the modulated illumination to the Speed OPIOM resonance and adopting a phase-sensitive detection scheme that ensures noise rejection, we enhanced the sensitivity and the signal-to-noise ratio for fluorescence detection in blot assays by factors of 50 and 10, respectively, over direct fluorescence observation under constant illumination. Then, we overcame the strong autofluorescence of growth media that are currently used in microbiology and realized multiplexed fluorescence observation of colonies of spectrally similar fluorescent bacteria with a unique configuration of excitation and emission wavelengths. Finally, we easily discriminated fluorescent labels from the autofluorescent and reflective background in labeled leaves, even under the interference of incident light at intensities that are comparable to sunlight. The proposed approach is expected to find multiple applications, from biological assays to outdoor observations, in fluorescence macroimaging.
Probing the upper band gap of atomic rhenium disulfide layers
Krishna P. Dhakal, Hyunmin Kim, Seonwoo Lee, Youngjae Kim, JaeDong Lee, et al.
Published. 2018, 7(6) : 945-955 doi: 10.1038/s41377-018-0100-3
Here, we investigate the ultrafast carrier dynamics and electronic states of exfoliated ReS2 films using time-resolved second harmonic generation (TSHG) microscopy and density functional theory (DFT) calculations. The second harmonic generation (SHG) of layers with various thicknesses is probed using a 1.19-eV beam. Up to ~13 nm, a gradual increment is observed, followed by a decrease caused by bulk interferometric light absorption. The addition of a pump pulse tuned to the exciton band gap (1.57 eV) creates a decay-to-rise TSHG profile as a function of the probe delay. The power and thickness dependencies indicate that the electron–hole recombination is mediated by defects and surfaces. The two photon absorptions of 2.38 eV in the excited state that are induced by pumping from 1.57 to 1.72 eV are restricted because these transitions highly correlate with the forbidden dd intrasubshell orbital transitions. However, the combined usage of a frequency-doubled pump (2.38 eV) with wavelength-variant SHG probes (2.60–2.82 eV) allows us to vividly monitor the variations in TSHG profiles from decay-to-rise to rise-to-decay, which imply the existence of an additional electron absorption state (s-orbital) at an approximate distance of 5.05 eV from the highest occupied molecular orbital states. This observation was critically examined by considering the allowance of each electronic transition and a small upper band gap (~0.5 eV) using modified DFT calculations.
Neuronal photoactivation through second-harmonic near-infrared absorption by gold nanoparticles
Wieteke D. A. M. de Boer, Jan J. Hirtz, Antonio Capretti, Tom Gregorkiewicz, Mercè Izquierdo-Serra, et al.
Published. 2018, 7(6) : 988-1000 doi: 10.1038/s41377-018-0103-0
Optical activation of neurons requires genetic manipulation or the use of chemical photoactivators with undesirable side effects. As a solution to these disadvantages, here, we demonstrate optically evoked neuronal activity in mouse cortical neurons in acute slices and in vivo by nonlinear excitation of gold nanoparticles. In addition, we use this approach to stimulate individual epitheliomuscular cells and evoke body contractions in Hydra vulgaris. To achieve this, we use a low-power pulsed near-infrared excitation at the double-wavelength of the plasmon resonance of gold nanoparticles, which enables optical sectioning and allows for high spatial precision and large penetration depth. The effect is explained by second-harmonic Mie scattering, demonstrating light absorption by a second-order nonlinear process, which enables photothermal stimulation of the cells. Our approach also minimizes photodamage, demonstrating a major advancement towards precise and harmless photoactivation for neuroscience and human therapeutics.
Wide-gamut lasing from a single organic chromophore
S. Lane, S. Vagin, H. Wang, W. R. Heinz, W. Morrish, et al.
Published. 2018, 7(6) : 968-976 doi: 10.1038/s41377-018-0102-1
The development of wideband lasing media has deep implications for imaging, sensing, and display technologies. We show that a single chromophore can be engineered to feature wide-gamut fluorescence and lasing throughout the entire visible spectrum and beyond. This exceptional color tuning demonstrates a chemically controlled paradigm for light emission applications with precise color management. Achieving such extensive color control requires a molecular blueprint that yields a high quantum efficiency and a high solubility in a wide variety of liquids and solids while featuring a heterocyclic structure with good steric access to the lone pair electrons. With these requirements in mind, we designed a lasing chromophore that encloses a lasing color space twice as large as the sRGB benchmark. This record degree of color tuning can in principle be adapted to the solid state by incorporating the chromophore into polymer films. By appropriately engineering the base molecular structure, the widest range of lasing wavelengths observed for a conventional gain medium can be achieved, in turn establishing a possible route toward high-efficiency light emitters and lasers with near-perfect chromaticity.
Self-healable electroluminescent devices
Guojin Liang, Zhuoxin Liu, Funian Mo, Zijie Tang, Hongfei Li, et al.
Published. 2018, 7(6) : 977-987 doi: 10.1038/s41377-018-0096-8
Electroluminescent (EL) devices have been extensively integrated into multi-functionalized electronic systems in the role of the vitally constituent light-emitting part. However, the lifetime and reliability of EL devices are often severely restricted by concomitant damage, especially when the strain exceeds the mechanical withstanding limit. We report a self-healable EL device by adopting a modified self-healable polyacrylic acid hydrogel as the electrode and a self-healable polyurethane as a phosphor host to realize the first omni-layer-healable light-emitting device. The physicochemical properties of each functionalized layer can be efficiently restored after experiencing substantial catastrophic damage. As a result, the luminescent performance of the self-healable EL devices is well recovered with a high healing efficiency (83.2% for 10 healing cycles at unfixed spots, and 57.7% for 20 healing cycles at a fixed spot). In addition, inter-device healing has also been developed to realize a conceptual "LEGO"-like assembly process at the device level for light-emitting devices. The design and realization of the self-healable EL devices may revive their performance and expand their lifetime even after undergoing a deadly cut. Our self-healable EL devices may serve as model systems for electroluminescent applications of the recently developed ionically conductive healable hydrogels and dielectric polymers.
High-resolution, in vivo multimodal photoacoustic microscopy, optical coherence tomography, and fluorescence microscopy imaging of rabbit retinal neovascularization
Wei Zhang, Yanxiu Li, Van Phuc Nguyen, Ziyi Huang, Zhipeng Liu, et al.
Published. 2018, 7(6) : 956-967 doi: 10.1038/s41377-018-0093-y
Photoacoustic microscopy (PAM) is an emerging imaging technology that can non-invasively visualize ocular structures in animal eyes. This report describes an integrated multimodality imaging system that combines PAM, optical coherence tomography (OCT), and fluorescence microscopy (FM) to evaluate angiogenesis in larger animal eyes. High-resolution in vivo imaging was performed in live rabbit eyes with vascular endothelial growth factor (VEGF)-induced retinal neovascularization (RNV). The results demonstrate that our multimodality imaging system can non-invasively visualize RNV in both albino and pigmented rabbits to determine retinal pathology using PAM and OCT and verify the leakage of neovascularization using FM and fluorescein dye. This work presents high-resolution visualization of angiogenesis in rabbits using a multimodality PAM, OCT, and FM system and may represent a major step toward the clinical translation of the technology.
Inverse photonic design of functional elements that focus Bloch surface waves
Yannick Augenstein, Andreas Vetter, Babak Vosoughi Lahijani, Hans Peter Herzig, Carsten Rockstuhl, et al.
Published. 2018, 7(6) : 1019-1027 doi: 10.1038/s41377-018-0106-x
Bloch surface waves (BSWs) are sustained at the interface of a suitably designed one-dimensional (1D) dielectric photonic crystal and an ambient material. The elements that control the propagation of BSWs are defined by a spatially structured device layer on top of the 1D photonic crystal that locally changes the effective index of the BSW. An example of such an element is a focusing device that squeezes an incident BSW into a tiny space. However, the ability to focus BSWs is limited since the index contrast achievable with the device layer is usually only on the order of Δn≈0.1 for practical reasons. Conventional elements, e.g., discs or triangles, which rely on a photonic nanojet to focus BSWs, operate insufficiently at such a low index contrast. To solve this problem, we utilize an inverse photonic design strategy to attain functional elements that focus BSWs efficiently into spatial domains slightly smaller than half the wavelength. Selected examples of such functional elements are fabricated. Their ability to focus BSWs is experimentally verified by measuring the field distributions with a scanning near-field optical microscope. Our focusing elements are promising ingredients for a future generation of integrated photonic devices that rely on BSWs, e.g., to carry information, or lab-on-chip devices for specific sensing applications.
Plasmonic mid-infrared third harmonic generation in germanium nanoantennas
Marco P. Fischer, Aaron Riede, Kevin Gallacher, Jacopo Frigerio, Giovanni Pellegrini, et al.
Published. 2018, 7(6) : 1001-1007 doi: 10.1038/s41377-018-0108-8
We demonstrate third harmonic generation in plasmonic antennas consisting of highly doped germanium grown on silicon substrates and designed to be resonant in the mid-infrared frequency range that is inaccessible with conventional nonlinear plasmonic materials. Owing to the near-field enhancement, the result is an ultrafast, subdiffraction, coherent light source with a wavelength tunable between 3 and 5 µm, and ideally overlapping with the fingerprint region of molecular vibrations. To observe the nonlinearity in this challenging spectral window, a high-power femtosecond laser system equipped with parametric frequency conversion in combination with an all-reflective confocal microscope setup is employed. We demonstrate spatially resolved maps of the linear scattering cross section and the nonlinear emission of single isolated antenna structures. A clear third-order power dependence as well as mid-infrared emission spectra prove the nonlinear nature of the light emission. Simulations support the observed resonance length of the double-rod antenna and demonstrate that the field enhancement inside the antenna material is responsible for the nonlinear frequency mixing.
Full-field interferometric imaging of propagating action potentials
Tong Ling, Kevin C. Boyle, Georges Goetz, Peng Zhou, Yi Quan, et al.
Published. 2018, 7(6) : 1008-1018 doi: 10.1038/s41377-018-0107-9
Currently, cellular action potentials are detected using either electrical recordings or exogenous fluorescent probes that sense the calcium concentration or transmembrane voltage. Ca imaging has a low temporal resolution, while voltage indicators are vulnerable to phototoxicity, photobleaching, and heating. Here, we report full-field interferometric imaging of individual action potentials by detecting movement across the entire cell membrane. Using spike-triggered averaging of movies synchronized with electrical recordings, we demonstrate deformations up to 3 nm (0.9 mrad) during the action potential in spiking HEK-293 cells, with a rise time of 4 ms. The time course of the optically recorded spikes matches the electrical waveforms. Since the shot noise limit of the camera (~2 mrad/pix) precludes detection of the action potential in a single frame, for all-optical spike detection, images are acquired at 50 kHz, and 50 frames are binned into 1 ms steps to achieve a sensitivity of 0.3 mrad in a single pixel. Using a self-reinforcing sensitivity enhancement algorithm based on iteratively expanding the region of interest for spatial averaging, individual spikes can be detected by matching the previously extracted template of the action potential with the optical recording. This allows all-optical full-field imaging of the propagating action potentials without exogeneous labels or electrodes.
Motility-based label-free detection of parasites in bodily fluids using holographic speckle analysis and deep learning
Yibo Zhang, Hatice Ceylan Koydemir, Michelle M. Shimogawa, Sener Yalcin, Alexander Guziak, et al.
Published. 2018, 7(6) : 1028-1045 doi: 10.1038/s41377-018-0110-1
Parasitic infections constitute a major global public health issue. Existing screening methods that are based on manual microscopic examination often struggle to provide sufficient volumetric throughput and sensitivity to facilitate early diagnosis. Here, we demonstrate a motility-based label-free computational imaging platform to rapidly detect motile parasites in optically dense bodily fluids by utilizing the locomotion of the parasites as a specific biomarker and endogenous contrast mechanism. Based on this principle, a cost-effective and mobile instrument, which rapidly screens ~3.2 mL of fluid sample in three dimensions, was built to automatically detect and count motile microorganisms using their holographic time-lapse speckle patterns. We demonstrate the capabilities of our platform by detecting trypanosomes, which are motile protozoan parasites, with various species that cause deadly diseases affecting millions of people worldwide. Using a holographic speckle analysis algorithm combined with deep learning-based classification, we demonstrate sensitive and label-free detection of trypanosomes within spiked whole blood and artificial cerebrospinal fluid (CSF) samples, achieving a limit of detection of ten trypanosomes per mL of whole blood (~five-fold better than the current state-of-the-art parasitological method) and three trypanosomes per mL of CSF. We further demonstrate that this platform can be applied to detect other motile parasites by imaging Trichomonas vaginalis, the causative agent of trichomoniasis, which affects 275 million people worldwide. With its cost-effective, portable design and rapid screening time, this unique platform has the potential to be applied for sensitive and timely diagnosis of neglected tropical diseases caused by motile parasites and other parasitic infections in resource-limited regions.
Optoacoustic microscopy at multiple discrete frequencies
Stephan Kellnberger, Dominik Soliman, George J. Tserevelakis, Markus Seeger, Hong Yang, et al.
Published. 2018, 7(6) : 1046-1057 doi: 10.1038/s41377-018-0101-2
Optoacoustic (photoacoustic) sensing employs illumination of transient energy and is typically implemented in the time domain using nanosecond photon pulses. However, the generation of high-energy short photon pulses requires complex laser technology that imposes a low pulse repetition frequency (PRF) and limits the number of wavelengths that are concurrently available for spectral imaging. To avoid the limitations of working in the time domain, we have developed frequency-domain optoacoustic microscopy (FDOM), in which light intensity is modulated at multiple discrete frequencies. We integrated FDOM into a hybrid system with multiphoton microscopy, and we examine the relationship between image formation and modulation frequency, showcase high-fidelity images with increasing numbers of modulation frequencies from phantoms and in vivo, and identify a redundancy in optoacoustic measurements performed at multiple frequencies. We demonstrate that due to high repetition rates, FDOM achieves signal-to-noise ratios similar to those obtained by time-domain methods, using commonly available laser diodes. Moreover, we experimentally confirm various advantages of the frequency-domain implementation at discrete modulation frequencies, including concurrent illumination at two wavelengths that are carried out at different modulation frequencies as well as flow measurements in microfluidic chips and in vivo based on the optoacoustic Doppler effect. Furthermore, we discuss how FDOM redefines possibilities for optoacoustic imaging by capitalizing on the advantages of working in the frequency domain.
Tunable optical spin Hall effect in a liquid crystal microcavity
Katarzyna Lekenta, Mateusz Król, Rafał Mirek, Karolina Łempicka, Daniel Stephan, et al.
Published. 2018, 7(6) : 650-655 doi: 10.1038/s41377-018-0076-z
The spin Hall effect, a key enabler in the field of spintronics, underlies the capability to control spin currents over macroscopic distances. The effect was initially predicted by D'Yakonov and Perel1 and has been recently brought to the foreground by its realization in paramagnetic metals by Hirsch2 and in semiconductors3 by Sih et al. Whereas the rapid dephasing of electrons poses severe limitations to the manipulation of macroscopic spin currents, the concept of replacing fermionic charges with neutral bosons such as photons in stratified media has brought some tangible advances in terms of comparatively lossless propagation and ease of detection4-7. These advances have led to several manifestations of the spin Hall effect with light, ranging from semiconductor microcavities8, 9 to metasurfaces10. To date the observations have been limited to built-in effective magnetic fields that underpin the formation of spatial spin currents. Here we demonstrate external control of spin currents by modulating the splitting between transverse electric and magnetic fields in liquid crystals integrated in microcavities.
Xenos peckii vision inspires an ultrathin digital camera
Dongmin Keum, Kyung-Won Jang, Daniel S. Jeon, Charles S. H. Hwang, Elke K. Buschbeck, et al.
Published. 2018, 7(6) : 656-662 doi: 10.1038/s41377-018-0081-2
Increased demand for compact devices leads to rapid development of miniaturized digital cameras. However, conventional camera modules contain multiple lenses along the optical axis to compensate for optical aberrations that introduce technical challenges in reducing the total thickness of the camera module. Here, we report an ultrathin digital camera inspired by the vision principle of Xenos peckii, an endoparasite of paper wasps. The male Xenos peckii has an unusual visual system that exhibits distinct benefits for high resolution and high sensitivity, unlike the compound eyes found in most insects and some crustaceans. The biologically inspired camera features a sandwiched configuration of concave microprisms, microlenses, and pinhole arrays on a flat image sensor. The camera shows a field-of-view (FOV) of 68 degrees with a diameter of 3.4 mm and a total track length of 1.4 mm. The biologically inspired camera offers a new opportunity for developing ultrathin cameras in medical, industrial, and military fields.
High-fidelity multimode fibre-based endoscopy for deep brain in vivo imaging
Sergey Turtaev, Ivo T. Leite, Tristan Altwegg-Boussac, Janelle M. P. Pakan, Nathalie L. Rochefort, et al.
Published. 2018, 7(6) : 663-670 doi: 10.1038/s41377-018-0094-x
Progress in neuroscience relies on new techniques for investigating the complex dynamics of neuronal networks. An ongoing challenge is to achieve minimally invasive and high-resolution observations of neuronal activity in vivo inside deep brain areas. Recently introduced methods for holographic control of light propagation in complex media enable the use of a hair-thin multimode optical fibre as an ultranarrow imaging tool. Compared to endoscopes based on graded-index lenses or fibre bundles, this new approach offers a footprint reduction exceeding an order of magnitude, combined with a significant enhancement in resolution. We designed a compact and high-speed system for fluorescent imaging at the tip of a fibre, achieving a resolution of 1.18 ± 0.04 µm across a 50-µm field of view, yielding 7-kilopixel images at a rate of 3.5 frames/s. Furthermore, we demonstrate in vivo observations of cell bodies and processes of inhibitory neurons within deep layers of the visual cortex and hippocampus of anaesthetised mice. This study paves the way for modern microscopy to be applied deep inside tissues of living animal models while exerting a minimal impact on their structural and functional properties.
Sharpening emitter localization in front of a tuned mirror
Hannah S. Heil, Benjamin Schreiber, Ralph Götz, Monika Emmerling, Marie-Christine Dabauvalle, et al.
Published. 2018, 7(6) : 671-678 doi: 10.1038/s41377-018-0104-z
Single-molecule localization microscopy (SMLM) aims for maximized precision and a high signal-to-noise ratio1. Both features can be provided by placing the emitter in front of a metal-dielectric nanocoating that acts as a tuned mirror2-4. Here, we demonstrate that a higher photon yield at a lower background on biocompatible metal-dielectric nanocoatings substantially improves SMLM performance and increases the localization precision by up to a factor of two. The resolution improvement relies solely on easy-to-fabricate nanocoatings on standard glass coverslips and is spectrally and spatially tunable by the layer design and wavelength, as experimentally demonstrated for dual-color SMLM in cells.
Reactive optical matter: light-induced motility in electrodynamically asymmetric nanoscale scatterers
Yuval Yifat, Delphine Coursault, Curtis W. Peterson, John Parker, Ying Bao, et al.
Published. 2018, 7(6) : 679-685 doi: 10.1038/s41377-018-0105-y
Subcellular spatial resolution achieved for deep-brain imaging in vivo using a minimally invasive multimode fiber
Sebastian A. Vasquez-Lopez, Raphaël Turcotte, Vadim Koren, Martin Plöschner, Zahid Padamsey, et al.
Published. 2018, 7(6) : 686-691 doi: 10.1038/s41377-018-0111-0
Achieving intravital optical imaging with diffraction-limited spatial resolution of deep-brain structures represents an important step toward the goal of understanding the mammalian central nervous system1-4. Advances in wavefront-shaping methods and computational power have recently allowed for a novel approach to high-resolution imaging, utilizing deterministic light propagation through optically complex media and, of particular importance for this work, multimode optical fibers (MMFs)5-7. We report a compact and highly optimized approach for minimally invasive in vivo brain imaging applications. The volume of tissue lesion was reduced by more than 100-fold, while preserving diffraction-limited imaging performance utilizing wavefront control of light propagation through a single 50-μm-core MMF. Here, we demonstrated high-resolution fluorescence imaging of subcellular neuronal structures, dendrites and synaptic specializations, in deep-brain regions of living mice, as well as monitored stimulus-driven functional Ca2+ responses. These results represent a major breakthrough in the compromise between high-resolution imaging and tissue damage, heralding new possibilities for deep-brain imaging in vivo.
News and Views
Turning losses into gain in nonlinear optics
Franco Prati
Published. 2018, 7(6) : 645-646 doi: 10.1038/s41377-018-0077-y
More than two decades trapped
Cheng-Wei Qiu, Lei-Ming Zhou
Published. 2018, 7(6) : 647-649 doi: 10.1038/s41377-018-0087-9
Optical tweezers, crowned by Nobel Prize the first time in 1990s, have widely impacted the research landscape of atom cooling, particle manipulation/sorting, and biology. After more than two decades of steady development, it received the deserving recognition once again in 2018. Unprecedented advancements across various disciplines are believed to be spurred furthermore by this important tool of optical manipulation.
"Perspective" – A new approach to serve our Light community
Dayong Jin, Jianlin Cao
Published. 2018, 7(6) : 643-644 doi: 10.1038/s41377-018-0085-y