Three-dimensional all-dielectric metamaterial solid immersion lens for subwavelength imaging at visible frequencies

Asymmetric Self-Assembly of Colloidal Superstructures in Nested Transient Emulsion Aerosols

Emulsions are versatile and robust platforms for colloidal self-assembly, but their ability to create complex and functional superstructures is hindered by the inherent symmetry of droplets. Here the creation of an aerosol of nested transient emulsion droplets with inherent asymmetry is reported, achieved by converging beams of water and 1-butanol mists. Self-assembly of nanoparticles occurs within such emulsion droplets as driven by the rapid two-phase interface diffusion, producing anisotropic superstructures. A unique hollowing process is observed due to the asymmetric diffusion of solvents, akin to the Kirkendall effect. This novel assembly platform offers several advantages, including asymmetric self-assembly in air, surfactant-free operation, and tunable droplet size. It enables the creation of clean, functional nanoparticle superstructures that can be easily disassembled when needed. These advancements pave the way for exploring intricate, anisotropic superstructures with diverse applications that are unavailable in conventional superstructures of spherical symmetry.

Superresolution based on coherent thermal radiation with selective information

We reexamine superresolution methods that may have been overlooked by previous optical microscopy techniques. For a one-dimensional (1D) system, we show that maximizing the information capacity of an imaging system is not a necessary condition for surpassing the Abbe diffraction limit. Specifically, the spatial resolution of two coherent emitters can go beyond the Abbe diffraction limit if an appropriate information zone, but not the full information zone, is selected for far-field imaging. Based on this principle, we show that λ/2.6 superresolution can be easily achieved for two coherent thermal radiative sources with a sufficiently large phase difference. Similar effects can be found for a 1D array of thermal radiative sources coupled by surface phonon polaritons. Introducing a dielectric microsphere into the system can further enhance the phase difference among the radiative sources, achieving superresolution better than λ/4. The concept and method presented here can be implemented to enhance the spatial resolution of thermal imaging.

Ultra-compact quintuple-band terahertz metamaterial biosensor for enhanced blood cancer diagnostics

Cancer and its diverse variations pose one of the most significant threats to human health and well-being. One of the most aggressive forms is blood cancer, originating from bone marrow cells and disrupting the production of normal blood cells. The incidence of blood cancer is steadily increasing, driven by both genetic and environmental factors. Therefore, early detection is crucial as it enhances treatment outcomes and improves success rates. However, accurate diagnosis is challenging due to the inherent similarities between normal and cancerous cells. Although various techniques are available for blood cancer identification, high-frequency imaging techniques have recently shown promise, particularly for real-time monitoring. Notably, terahertz (THz) frequencies offer unique advantages for biomedical applications. This research proposes an innovative terahertz metamaterial-based biosensor for high-efficacy blood cancer detection. The proposed structure is ultra-compact and operates across five bands within the range of 0.6 to 1.2 THz. It is constructed using a polyethylene terephthalate (PET) dielectric layer and two aluminum (Al) layers, with the top layer serving as a base for the THz-range resonator. Careful design, architectural arrangement, and optimization of the geometry parameters allow for achieving nearly perfect absorption rates (>95%) across all operating bands. The properties of the proposed sensor are extensively evaluated through full-wave electromagnetic (EM) analysis, which includes assessing the refractive index and the distribution of the electric field at individual working frequencies. The suitability for blood cancer diagnosis has been validated by integrating the sensor into a microwave imaging (MWI) system and conducting comprehensive simulation studies. These studies underscore the device's capability to detect abnormalities, particularly in distinguishing between healthy and cancerous cells. Benchmarking against state-of-the-art biosensors in recent literature indicates that the proposed sensor is highly competitive in terms of major performance indicators while maintaining a compact size.

Converting evanescent waves into propagating waves by hyper-hemi-microsphere

Hyper-hemi-microspheres (HHMS) have shown promise in enhancing super-resolution imaging when combined with conventional optical microscopy. To offer actionable guidance for optimizing HHMS and hold broad applicability in the field of super-resolution imaging, the mechanism underpinning the enhanced imaging facilitated by HHMS is revealed by deriving the conversion and transmission conditions for evanescent waves. This is achieved by elucidating the intricate interplay between evanescent wave conversion and factors including refractive index, thickness, and surroundings of HHMS. Using the finite-difference time-domain (FDTD) method, influences of various HHMS properties on the conversion and transmission process are analyzed in detail. To fully harness the potential of HHMS in super-resolution imaging, the immersion conditions are elucidated.

Acoustic Assembly and Scanning of Superlens Arrays for High-Resolution and Large Field-of-View Bioimaging

High-resolution and dynamic bioimaging is essential in life sciences and biomedical applications. In recent years, microspheres combined with optical microscopes have offered a low cost but promising solution for super-resolution imaging, by breaking the diffraction barrier. However, challenges still exist in precisely and parallelly superlens controlling using a noncontact manner, to meet the demands of large-area scanning imaging for desired targets. This study proposes an acoustic wavefield-based strategy for assembling and manipulating micrometer-scale superlens arrays, in addition to achieving on-demand scanning imaging through phase modulation. In experiments, acoustic pressure nodes are designed to be comparable in size to microspheres, allowing spatially dispersed microspheres to be arranged into arrays with one unit per node. Droplet microlenses with various diameters can be adapted in the array, allowing for a wide range of spacing periods by applying different frequencies. In addition, through the continuous phase shifting in the x and y directions, this acoustic superlens array achieves on-demand moving for the parallel high-resolution virtual image capturing and scanning of nanostructures and biological cell samples. As a comparison, this noncontact and cost-effective acoustic manner can obtain more than ∼100 times the acquisition efficiency of a single lens, holding promise in advancing super-resolution microscopy and subcellular-level bioimaging.

Shell buckling for programmable metafluids

The pursuit of materials with enhanced functionality has led to the emergence of metamaterials-artificially engineered materials whose properties are determined by their structure rather than composition. Traditionally, the building blocks of metamaterials are arranged in fixed positions within a lattice structure1-19. However, recent research has revealed the potential of mixing disconnected building blocks in a fluidic medium20-27. Inspired by these recent advances, here we show that by mixing highly deformable spherical capsules into an incompressible fluid, we can realize a 'metafluid' with programmable compressibility, optical behaviour and viscosity. First, we experimentally and numerically demonstrate that the buckling of the shells endows the fluid with a highly nonlinear behaviour. Subsequently, we harness this behaviour to develop smart robotic systems, highly tunable logic gates and optical elements with switchable characteristics. Finally, we demonstrate that the collapse of the shells upon buckling leads to a large increase in the suspension viscosity in the laminar regime. As such, the proposed metafluid provides a promising platform for enhancing the functionality of existing fluidic devices by expanding the capabilities of the fluid itself.

Roadmap on Label-Free Super-Resolution Imaging

Label-free super-resolution (LFSR) imaging relies on light-scattering processes in nanoscale objects without a need for fluorescent (FL) staining required in super-resolved FL microscopy. The objectives of this Roadmap are to present a comprehensive vision of the developments, the state-of-the-art in this field, and to discuss the resolution boundaries and hurdles which need to be overcome to break the classical diffraction limit of the LFSR imaging. The scope of this Roadmap spans from the advanced interference detection techniques, where the diffraction-limited lateral resolution is combined with unsurpassed axial and temporal resolution, to techniques with true lateral super-resolution capability which are based on understanding resolution as an information science problem, on using novel structured illumination, near-field scanning, and nonlinear optics approaches, and on designing superlenses based on nanoplasmonics, metamaterials, transformation optics, and microsphere-assisted approaches. To this end, this Roadmap brings under the same umbrella researchers from the physics and biomedical optics communities in which such studies have often been developing separately. The ultimate intent of this paper is to create a vision for the current and future developments of LFSR imaging based on its physical mechanisms and to create a great opening for the series of articles in this field.

Wide-Field and Real-Time Super-Resolution Optical Imaging By Titanium Dioxide Nanoparticle-Assembled Solid Immersion Lens

Super-resolution optical imaging techniques can break the optical diffraction limit, thus providing unique opportunities to visualize the microscopic world at the nanoscale. Although near-field optical microscopy techniques have been proven to achieve significantly improved imaging resolution, most near-field approaches still suffer from a narrow field of view (FOV) or difficulty in obtaining wide-field images in real time, which may limit their widespread and diverse applications. Here, the authors experimentally demonstrate an optical microscope magnification and image enhancement approach by using a submillimeter-sized solid immersion lens (SIL) assembled by densely-packed 15 nm TiO₂ nanoparticles through a silicone oil two-step dehydration method. This TiO₂ nanoparticle-assembled SIL can achieve both high transparency and high refractive index, as well as sufficient mechanical strength and easy-to-handle size, thus providing a fast, wide-field, real-time, non-destructive, and low-cost solution for improving the quality of optical microscopic observation of a variety of samples, including nanomaterials, cancer cells, and living cells or bacteria under conventional optical microscopes. This study provides an attractive alternative to simplify the fabrication and applications of high-performance SILs.

Double-negative metamaterial square enclosed Q.S.S.R For microwave sensing application in S-band with high sensitivity and Q-factor

Metamaterials have gained much attention due to their exciting characteristics and potential uses in constructing valuable technologies. This paper presents a double negative square resonator shape metamaterial sensor to detect the material and its thickness. An innovative double-negative metamaterial sensor for microwave sensing applications is described in this paper. It has a highly sensitive Q-factor and has good absorption characteristics approximately equal to one. For the metamaterial sensor, the recommended measurement is 20 by 20 mm. Computer simulation technology (C.S.T.) microwave studios are used to design the metamaterial structure and figure out its reflection coefficient. Various parametric analyses have been performed to optimize the design and size of the structure. The experimental and theoretical results are shown for a metamaterial sensor that is attached to five different materials such as, Polyimide, Rogers RO3010, Rogers RO4350, Rogers RT5880, and FR-4. A sensor's performance is evaluated using three different thicknesses of FR-4. There is a remarkable similarity between the measured and simulated outcomes. The sensitivity values for 2.88 GHz and 3.5 GHz are 0.66% and 0.19%, respectively, the absorption values for both frequencies are 99.9% and 98.9%, respectively, and the q-factor values are 1413.29 and 1140.16, respectively. In addition, the figure of merit (FOM) is analyzed, and its value is 934.18. Furthermore, the proposed structure has been tested against absorption sensor applications for the purpose of verifying the sensor's performance. With a high sense of sensitivity, absorption, and Q-factor, the recommended sensor can distinguish between thicknesses and materials in various applications.

Sub-50 nm optical imaging in ambient air with 10× objective lens enabled by hyper-hemi-microsphere

Optical microsphere nanoscope has great potential in the inspection of integrated circuit chips for semiconductor industry and morphological characterization in biology due to its superior resolving power and label-free characteristics. However, its resolution in ambient air is restricted by the magnification and numerical aperture (NA) of microsphere. High magnification objective lens is required to be coupled with microsphere for nano-imaging beyond the diffraction limit. To overcome these challenges, in this work, high refractive index hyper-hemi-microspheres with tunable magnification up to 10× are proposed and realized by accurately tailoring their thickness with focused ion beam (FIB) milling. The effective refractive index is put forward to guide the design of hyper-hemi-microspheres. Experiments demonstrate that the imaging resolution and contrast of a hyper-hemi-microsphere with a higher magnification and larger NA excel those of a microsphere in air. Besides, the hyper-hemi-microsphere could resolve ~50 nm feature with higher image fidelity and contrast compared with liquid immersed high refractive index microspheres. With a hyper-hemi-microsphere composed microscale compound lens configuration, sub-50 nm optical imaging in ambient air is realized by only coupling with a 10× objective lens (NA = 0.3), which enhances a conventional microscope imaging power about an order of magnitude.

Addressing the imaging limitations of a microsphere-assisted nanoscope

In the past decade, microsphere-assisted nanoscopy has been developed rapidly to overcome the diffraction limit. However, due to the limited size and high surface curvature of microspheres, the magnified imaging still suffers from problems like limited view scope, imaging distortion, and low contrast. In this paper, we specialize in the imaging mechanism of microspheres and find irradiance as the key factor for microsphere imaging quality. Utilizing a modified optical tweezer system, we achieve precise manipulation of microspheres and further propose a high-quality large-field magnified imaging scheme. The results show that the imaging area of 5 µm microspheres can reach 16×12 µm² with the minimum identifiable feature of 137 nm. This scheme provides a new solution for extending the measuring scope of microsphere-assisted nanoscope, and will certainly promote the application of this technology in practice.

Full-field high-resolution terahertz imaging based on a high-resistance silicon solid immersion lens

The spatial resolution of the direct imaging system depends on the wavelength and the numerical aperture. In the terahertz (THz) waveband, the wavelength is relatively large, and the higher numerical aperture of the imaging system usually promises the possibility of achieving higher spatial resolution. Solid immersion technique is an effective method to expand the numerical aperture. We design and fabricate a hemisphere lens with high-resistance silicon to achieve the effect of solid immersion, and obtain full-field, high-resolution focal-plane imaging. The characteristics of the direct refraction imaging and the secondary reflection imaging are analyzed by ray-tracing calculations. And the field curvature of the equivalent object plane and the spot diagram on the vertical image plane of the lens are quantifiably evaluated. It is shown that the secondary reflection imaging can effectively reduce the geometric distortion and achieve more ideal imaging quality. The method of blocking different regions before and after the solid immersion lens is proposed to obtain a clear magnified image of a two-dimensional grating with the period of 300 µm. This method provides a powerful tool for THz full-field microscopic imaging.

Microlens-assisted microscopy for biology and medicine

The addition of dielectric transparent microlens in the optical scheme is an effective and at the same time simple and inexpensive way to increase the resolution of a light microscope. For these purposes, spherical and cylindrical microlenses with a diameter of 1-100 μm are usually used. The microlens focuses the light into a narrow beam called a photonic nanojet. An enlarged virtual image is formed, which is captured by the objective of the light microscope. In addition to microscopy, the microlenses are successfully applied to amplify optical signals, increase the trapping force of optical tweezers and are used in microsurgery. This review considers the design and principle of microlens-assisted microscopes. Taking into account the advantages of the super-resolution optical methods for research in life science, the examples of the use of the microlenses in biomedical practice are discussed in detail.

Broadband achromatic aberration general conformal Luneburg lens with quasi-far-field highly efficient super-focusing

Super-focusing light using metamaterials and metasurfaces is of paramount importance in several applications, from integrated optics to microwave engineering and sensing. However, there are still some difficulties to realize broadband achromatic aberration highly efficient super-focusing from the far field to far field or quasi far field. In this Letter, based on conformal transformation optics, we propose a generalized conformal Luneburg lens (GCLL), which provides a new, to the best of our knowledge, strategy for quasi-far-field super-focusing with broadband (0.9-1.3 THz) achromatic aberration and high efficiency (above 60%). A relatively high numerical aperture (NA of 0.63) and sub-diffraction-limited resolution (FWHM of 0.45λ) are also obtained. The sample of the GCLL was designed using gradient metamaterials. The numerical simulation results verify that the focusing effects of the designed samples are consistent with the performance of the ideal GCLL.

Special Issue on Photonic Jet: Science and Application

Photonic jets (PJs) are important mesoscale optical phenomena arising from electromagnetic waves interacting with dielectric particles with sizes around several to several tens wavelengths (~2–40 λ) [...]

Selective mode excitations and spontaneous emission engineering in quantum emitter-photonic structure coupled systems

We study the excitation conditions of the supported field modes, as well as the spontaneous decay property of a two-level quantum emitter coupled to photonic structures containing topological insulators (TIs) and left-handed materials. Within the proper field quantization scheme, the spontaneous decay rates of dipoles with different polarizations are expressed in forms of the Green's functions. We find that in the proposed structure, the variation in the topological magnetoelectric polarizability (TMP) has a deterministic effect on the excitation of different field modes. As the result, the spontaneous decay property of the quantum emitter can be engineered. For a dipole placed in different spatial regions, the spontaneous decay feature indicates a dominant contribution from the waveguide modes, the surface plasmon modes or the free vacuum modes. Moreover, a special kind of the surface plasmon modes displaying asymmetric density of states at the interfaces, becomes legal in the presence of nontrivial TIs. These phenomena manifest the feasibility in controlling dipole emissions via manipulations of the topological magnetoelectric (TME) effect. Our results have potential applications in quantum technologies relied on the accurate control over light-matter interactions.

Correlative AFM and Scanning Microlens Microscopy for Time-Efficient Multiscale Imaging

With the rapid evolution of microelectronics and nanofabrication technologies, the feature sizes of large-scale integrated circuits continue to move toward the nanoscale. There is a strong need to improve the quality and efficiency of integrated circuit inspection, but it remains a great challenge to provide both rapid imaging and circuit node-level high-resolution images simultaneously using a conventional microscope. This paper proposes a nondestructive, high-throughput, multiscale correlation imaging method that combines atomic force microscopy (AFM) with microlens-based scanning optical microscopy. In this method, a microlens is coupled to the end of the AFM cantilever and the sample-facing side of the microlens contains a focused ion beam deposited tip which serves as the AFM scanning probe. The introduction of a microlens improves the imaging resolution of the AFM optical system, providing a 3-4× increase in optical imaging magnification while the scanning imaging throughput is improved ≈8×. The proposed method bridges the resolution gap between traditional optical imaging and AFM, achieves cross-scale rapid imaging with micrometer to nanometer resolution, and improves the efficiency of AFM-based large-scale imaging and detection. Simultaneously, nanoscale-level correlation between the acquired optical image and structure information is enabled by the method, providing a powerful tool for semiconductor device inspection.

Sub-50 nm control of light at 405 nm with planar Si nanolens

We studied the super-resolution light modulation capability of Si nanodisks, a flat semi-transparent high index nanolens in the visible spectral range. A Laguerre-Gaussian beam-based optimization algorithm was developed to synthesize desired field distributions. Focused spots below 45 nm (< λ/9) were successfully achieved with 405 nm light over the whole center area of the nanolens. This superb light nano-focusing capability allows us to synthesize complex nano-patterns by simply superposing several focus spots together, making the Si nanolens a promising tool for super-resolution photolithography.

Numerical Calculation of the Light Propagation in Tapered Optical Fibers for Optical Neural Interfaces

As implantable optical systems recently enabled new approaches to study the brain with optical radiations, tapered optical fibers emerged as promising implantable waveguides to deliver and collect light from sub-cortical structures of the mouse brain. They rely on a specific feature of multimodal fiber optics: as the waveguide narrows, the number of guided modes decreases and the radiation can gradually couple with the environment. This happens along a taper segment whose length can be tailored to match with the depth of functional structures of the mouse brain, and can extend for a few millimeters. This anatomical requirement results in optical systems which have an active area that is very long compared to the wavelength of the light they guide and their behavior is typically estimated by ray tracing simulations, because finite element methods are too computationally demanding. Here we present a computational technique that exploits the beam-envelope method and the cylindrical symmetry of the fibers to provide an efficient and exact calculation of the electric field along the fibers, which may enable the design of neural interfaces optimized to meet different goals.

Super-resolution scanning imaging based on metal-dielectric composite metamaterials

We propose super-resolution scanning imaging by using a metamaterial composed of a silver-silicon dioxide composite covered by a layer of chromium containing one slit and a silicon dioxide substrate. By simulating a distribution of energy flow in the metamaterial for an H-polarized wave, we find that the output beam exhibits focusing accompanied with good directional radiation, which is able to be designed as a super-resolution scanning probe. We also demonstrate numerically super-resolution imaging by scanning our designed metamaterial over a sub-wavelength object.

Anisotropy Characterization of Metallic Lens Structures

This paper presents a full electromagnetic (EM) characterization of metallic lenses. The method is based on the utilization of free-space transmission and reflection coefficients to accurately obtain lenses’ tensorial EM parameters. The applied method reveals a clear anisotropic behavior with a full tensorial directional permittivity and permeability and noticeably dispersive permeability and wave impedance. This method yields accurate values for the effective refractive index, wave impedance, permittivity, and permeability, unlike those obtained by simple methods such as the eigenmode method. These correct cell parameters affect their lens performance, as manifested in a clear level of anisotropy, impedance matching, and losses. The effect of anisotropy caused by oblique incidence on the performance and operation of lens designs is illustrated in a lens design case.

In silico study of natural compounds from sesame against COVID-19 by targeting Mpro, PLpro and RdRp

Natural products and traditional medicine products with known safety profiles are a promising source for the discovery of new drug leads. Natural products as sesame were reported to exhibit potential to protect from COVID-19 disease. In our study, the total methanolic extract of Sesamum indicum L. seeds (sesame) were led to isolation of seven known compounds, five lignan; sesamin 1, sesamolin 2, pinoresinol 3, hydroxymatairesinol 6, spicatolignan 7, together with two simple phenolic compounds; ferulic acid 4 and vanillic acid 5. All isolated compounds were evaluated in silico against three important SARS-CoV-2 protein targets; main protease (Mpro), papain-like protease (PLpro) and RNA-dependent RNA polymerase (RdRp) which possessed crucial role in replication and proliferation of the virus inside the human cell. The results revealed that compound 6 has the high affinity against the three main proteins, specially towards the SARS-CoV-2 Mpro that exceeded the currently used SARS-CoV-2 Mpro inhibitor darunavir as well as, exhibiting a similar binding energy at SARS CoV-2 PLpro when compared with the co-crystallized ligand. This activity continued to include the RdRp as it displayed a comparable docking score with remdesivir. Inferiorly, compounds 1 and 2 showed also similar triple inhibitory effect against the three main proteins while compound 7 exhibited a dual inhibitory effect against SARS CoV-2 PLPro and RdRp. Further molecular dynamic simulation experiments were performed to validate these docking experiments and to calculate their binding free energies (ΔGs). Compounds 1, 2, 3, 6, and 7 showed comparable binding stability inside the active site of each enzyme with ΔG values ranged from -4.9 to -8.8 kcal mol-1. All the compounds were investigated for their ADME and drug likeness properties, which showed acceptable ADME properties and obeying Lipinski's rule of five parameters. It can be concluded that the isolated compounds from sesame lignans could be an alternative source for the development of new natural leads against COVID-19.

High resolution imaging of viruses: Scanning probe microscopy and related techniques

Scanning probe microscopy is a group of measurements that provides 3D visualization of viruses in different environmental conditions including liquids and air. Besides 3D topography it is possible to measure the properties like mechanical rigidity and stability, adhesion, tendency to crystallization, surface charge, etc. Choosing the right substrate and scanning parameters makes it much easier to obtain reliable data. Rational interpretation of experimental results should take into account possible artifacts, proper filtering and data presentation using specially designed software packages. Animal and human virus characterization is in the focus of many intensive studies because of their potential harm to higher organisms. The article focuses on high-resolution visualization of plant viruses. Tobacco mosaic virus, potato viruses X and B and others are not dangerous for the human being and are widely used in different applications such as vaccine preparation, construction of building units in nanotechnology and material science applications, nanoparticle production and delivery, and even metrology. The methods of virus's deposition, visualization, and consequent image processing and interpretation are described in details. Specific examples of viruses imaging are illustrated using the FemtoScan Online software, which has typical and all the necessary built-in functions for constructing three-dimensional images, their processing and analysis. Despite visible progress in visualizing the viruses using probe microscopy, many unresolved problems still remain. At present time the probe microscopy data on viruses is not systemized. There is no descriptive atlas of the images and morphology as revealed by this type of high resolution microscopy. It is worth emphasizing that new virus investigation methods will appear due to the progress of science.

Super-Resolution Imaging by Dielectric Superlenses: TiO2 Metamaterial Superlens versus BaTiO3 Superlens

All-dielectric superlens made from micro and nano particles has emerged as a simple yet effective solution to label-free, super-resolution imaging. High-index BaTiO3 Glass (BTG) microspheres are among the most widely used dielectric superlenses today but could potentially be replaced by a new class of TiO2 metamaterial (meta-TiO2) superlens made of TiO2 nanoparticles. In this work, we designed and fabricated TiO2 metamaterial superlens in full-sphere shape for the first time, which resembles BTG microsphere in terms of the physical shape, size, and effective refractive index. Super-resolution imaging performances were compared using the same sample, lighting, and imaging settings. The results show that TiO2 meta-superlens performs consistently better over BTG superlens in terms of imaging contrast, clarity, field of view, and resolution, which was further supported by theoretical simulation. This opens new possibilities in developing more powerful, robust, and reliable super-resolution lens and imaging systems.

Magnifying lens designed by optical conformal mapping

We proposed an alternative method to design a magnifying lens by optical conformal mapping. Different from previous hyperlens or superlens, the proposed lens needs no materials with negative or anisotropic refractive index. The lens has better photonic transporting efficiency than conventional a solid immersion lens due to impedance matching. The proposed lenses have many other advantages, such as broadband, low loss, and no need to redesign the sizes and material parameters when another magnifying ratio is required. Both numerical simulations and experimental demonstrations are implemented to verify the performance of the lens.

Synergetic Effect of Plasmonic Gold Nanorods and MgO for Perovskite Solar Cells

We report new structured perovskite solar cells (PSCs) using solution-processed TiO₂/Au nanorods/MgO composite electron transport layers (ETLs). The proposed method is facile, convenient, and effective. Briefly, Au nanorods (NRs) were prepared and introduced into mesoporous TiO₂ ETLs. Then, thin MgO overlayers were grown on the Au NRs modified ETLs by wet spinning and pyrolysis of the magnesium salt. By simultaneous use of Au NRs and MgO, the power conversion efficiency of the PSC device increases from 14.7% to 17.4%, displaying over 18.3% enhancement, compared with the reference device without modification. Due to longitudinal plasmon resonances (LPRs) of gold nanorods, the embedded Au NRs exhibit the ability to significantly enhance the near-field and far-field (plasmonic scattering), increase the optical path length of incident photons in the device, and as a consequence, notably improve external quantum efficiency (EQE) at wavelengths above 600 nm and power conversion efficiency (PCE) of PSC solar cells. Meanwhile, the thin MgO overlayer also contributes to enhanced performance by reducing charge recombination in the solar cell. Theoretical calculations were carried out to elucidate the PV performance enhancement mechanisms.

Super-Resolution Imaging with Direct Laser Writing-Printed Microstructures

Dielectric microstructures coupled with a conventional optical microscope have been proven to be a successful way to achieve super-resolution imaging. However, a limitation of such super-resolution imaging is the microstructure fabrication ability, which generally provides natural structures (such as spherical, hemispherical, superhemispherical microlenses, and so on). Meanwhile, the influences of microstructures with complex shapes on the super-resolved imaging still remain unknown. In this paper, direct laser writing (DLW) lithography is used to produce a series of complex microstructures, which are capable of achieving super-resolution imaging in the optical far-field region. Cylinder, truncated cone, hemisphere, and protruding hemisphere microstructures are successfully fabricated by this 3D printing technology, allowing us to resolve features as small as 100 nm under classical microscopy. Moreover, different microstructures lead to different photonic nanojet (PNJ) illuminations and collection efficiencies, resulting in a critical role in super-resolved imaging. The microstructures with spherical surfaces can easily collect the light scattered by the object and convert the high-spatial-frequency evanescent waves into propagating waves.

Recent progress in understanding 2019 novel coronavirus (SARS-CoV-2) associated with human respiratory disease: detection, mechanisms and treatment

Viral respiratory diseases such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) always pose a severe threat to people. First identified in late December 2019, a novel coronavirus (2019-nCoV; SARS-CoV-2) has affected many provinces in China and multiple countries worldwide. The viral outbreak has aroused panic and a public-health emergency around the world, and the number of infections continues to rise. However, the causes and consequences of the pneumonia remain unknown. To effectively implement epidemic prevention, early identification and diagnosis are critical to disease control. Here we scrutinise a series of available studies by global scientists on the clinical manifestations, detection methods and treatment options for the disease caused by SARS-CoV-2, named coronavirus disease 2019 (COVID-19), and also propose potential strategies for preventing the infection.

Three-stage full-wave simulation architecture for in-depth analysis of microspheres in microscopy

Over a decade, considerable development has been achieved in microsphere microscopy; the popularity of this method is attributable to its compatibility with biomedical applications. Although microscopy has been used extensively, insufficient analyses and simulation approaches capable of explaining the experimental observations have hampered its theoretical development. In this paper, a three-stage full-wave simulation architecture has been presented for the in-depth analysis of the imaging properties of microspheres. This simulation architecture consists of forward and backward propagation mechanisms, following the concept of geometric optics and strictly complying to wave optics at each stage. Three numerical simulation methods, including FDTD, NTFF, and ASPW, are integrated into this simulation architecture to encompass near-field and far-field behaviors and relieve the computational burden. We validated this architecture by comparing our simulation results with the experimental data provided in literature. The results confirmed that the proposed architecture exhibits high consistency both qualitatively and quantitatively. By using this architecture, we demonstrated the near-field effect of the samples on the resolution and provided evidence to explain the conflicts in literature. Moreover, the flexibility and versatility of the proposed architecture in modeling allow adaptation to various scenarios in microsphere microscopy. The results of this study, as an imaging analysis and system design platform, may facilitate the development of microsphere microscopy for biomedical imaging, wafer inspection, and other potential applications.

Unibody microscope objective tipped with a microsphere: design, fabrication, and application in subwavelength imaging

Microsphere-based subwavelength imaging technique was first demonstrated in 2011. After nearly a decade of efforts, such technique has spawned numerous interests in fields such as laser nano-machining, imaging, sensing, and biological detection. For wider industrial-scale application of the technique, a robust and low-cost objective lens incorporating a microsphere lens is highly desired and sought by many researchers. In this work, we demonstrate a unibody microscope objective lens formed by tipping a high-index microsphere onto a plano-convex lens and subsequently fitting them into a conventional objective lens. We call this the plano-convex-microsphere (PCM) objective, which resembles the appearance and operation of an ordinary microscope objective while providing super-resolving power in discerning subwavelength 100 nm features ($\lambda /{4}.{7}$λ/4.7) in air and far-field conditions. The imaging performance of the PCM objective, along with the working distance, has been systematically investigated. It has a calibrated resolution of $\lambda /{3}$λ/3 in the far field, a numerical aperture of 1.57, and a working distance of 3.5 µm. With the assistance of a scanning process, larger-area imaging is realized. The PCM objective can be easily adapted to existing microscope systems and is appealing for commercialization.

Full three-dimensional Poynting vector flow analysis of great field-intensity enhancement in specifically sized spherical-particles

The Poynting vector plays a key role in electrodynamics as it is directly related to the power and the momentum carried by an electromagnetic wave. Based on the Lorenz-Mie theory, we report on the focusing effect of a spherical particle-lens by properly analysing the Poynting vector maps. Conventional two-dimensional (2D) maps showing Poynting vector magnitude and direction in a given plane cannot deliver information on three-dimensional (3D) directivity and vectorisation in key regions of singularities, such as vortexes and saddle points, due to poor expressiveness. In this article, an analytical 3D mapping technology is utilised to track the field-features passing through the singularities of the distribution of the Poynting vector in a spherically dielectric mesoscale particle-lens. We discovered that the spheres with the certain size parameters can stimulate extremely large field-intensity at singularities and then form two circular hotspots around the sphere poles. An astonishing large 'heart-shape' 3D Poynting vector circulation, which cannot be predicted by conventional 2D mapping analysis, is found to provide a great angular variation within an enormous range in these spheres. We anticipate that this effect will contribute to the field-enhancement phenomena, such as surface enhances Raman scattering, surface enhances absorption, super-resolution imaging and others.

Antibacterial and anticancer activities of asymmetric lollipop-like mesoporous silica nanoparticles loaded with curcumin and gentamicin sulfate

Asymmetric mesoporous silica nanoparticles with anisotropic geometry and dual-compartments are highly desired for loading and release of dual-drugs in separated storage spaces. In this study, an asymmetric lollipop-like mesoporous silica nanoparticle Fe₃O₄@SiO₂&EPMO (EPMO = ethane bridged periodic mesoporous organosilica) was successfully developed via an anisotropic epitaxial growth strategy. The asymmetric nanoparticles show a uniform lollipop shape with a head of spherical Fe₃O₄@SiO₂ core-shell that is 200 nm in diameter and a tail of EPMO nanorods with a length of ∼90 nm, and a specific surface area of ∼650.3 m² g^-1. Most importantly, the asymmetric nanoparticles possess the unique dual independent (hydrophilic/hydrophobic) spaces with good loading capacities and are significantly more efficient for cancer cell killing than pure drug based on in vitro studies. Additionally, the dual-drug-loaded nanoparticles exhibited excellent antibacterial activity.

Label-free difference super-resolution microscopy based on parallel detection

In this paper, a new method is proposed for super-resolution imaging of non-fluorescent samples. This approach is based on the intensity difference between confocal image and negative confocal image, which are simultaneously acquired at one sample scanning. In order to get these two different images simultaneously, the sample was illuminated by two different focused spots from the same laser source: the doughnut spot and the solid spot. The effectiveness of the label-free difference microscopy based on parallel detection was validated by experiments on some samples including 80 nm gold beads, 100 nm silver nanowires, and Blu-ray DVD without fluorescent dyes. By subtraction of the reflected light intensity from the sample, the final resolution of the image without deconvolution was enhanced about 1.6 times compared with confocal imaging. This technique can be applied to surface topography detection of metallographic or other non-fluorescent materials.

High performance perovskite solar cells using Cu9S5 supraparticles incorporated hole transport layers

We disclose novel photovoltaic device physics and present details of device mechanisms by investigating perovskite solar cells (PSCs) incorporating Cu₉S₅@SiO₂ supraparticles (SUPs) into Spiro-OMeTAD based hole transport layers (HTLs). High quality colloidal Cu₉S₅ nanocrystals (NCs) were prepared using a hot-injection approach. Multiple Cu₉S₅ NCs were further embedded in silica to construct a Cu₉S₅@SiO₂ SUP. Cu₉S₅@SiO₂ SUPs were blended into Spiro-OMeTAD based HTLs with different weight ratios. Theoretical and experimental results show that the very strong light scattering or reflecting properties of Cu₉S₅@SiO₂ SUPs blended in the PSC device in a proper proportion distribute to increase the light energy trapped within the device, leading to significant enhancement of light absorption in the active layer. Additionally, the incorporated Cu₉S₅@SiO₂ SUPs can also promote the electrical conductivity and hole-transport capacity of the HTL. Significantly larger conductivity and higher hole injection efficiency were demonstrated in the HTM with the optimal weight ratios of Cu₉S₅@SiO₂ SUPs. As a result, efficient Cu₉S₅ SUPs based PSC devices were obtained with average power conversion efficiency (PCE) of 18.21% at an optimal weight ratio of Cu₉S₅ SUPs. Compared with PSC solar cells without Cu₉S₅@SiO₂ SUPs (of which the average PCE is 14.38%), a remarkable enhancement over 26% in average PCE was achieved. This study provides an innovative approach to efficiently promote the performance of PSC devices by employing optically stable, low-cost and green p-type semiconductor SUPs.

Single-cell biomagnifier for optical nanoscopes and nanotweezers

Optical microscopes and optical tweezers, which were invented to image and manipulate microscale objects, have revolutionized cellular and molecular biology. However, the optical resolution is hampered by the diffraction limit; thus, optical microscopes and optical tweezers cannot be directly used to image and manipulate nano-objects. The emerging plasmonic/photonic nanoscopes and nanotweezers can achieve nanometer resolution, but the high-index material structures will easily cause mechanical and photothermal damage to biospecimens. Here, we demonstrate subdiffraction-limit imaging and manipulation of nano-objects by a noninvasive device that was constructed by trapping a cell on a fiber tip. The trapped cell, acting as a biomagnifier, could magnify nanostructures with a resolution of 100 nm (λ/5.5) under white-light microscopy. The focus of the biomagnifier formed a nano-optical trap that allowed precise manipulation of an individual nanoparticle with a radius of 50 nm. This biomagnifier provides a high-precision tool for optical imaging, sensing, and assembly of bionanomaterials.

Extraordinary Focusing Effect of Surface Nanolenses in Total Internal Reflection Mode

Microscopic lenses are paramount in solar energy harvesting, optical devices, and imaging technologies. This work reports an extraordinary focusing effect exhibited by a surface nanolens (i.e., with at least one dimension of subwavelength) that is situated in an evanescent field from the total internal reflection (TIR) of light illuminated to the supporting substrate above the critical angle. Our measurements show that the position, shape, and size of the surface area with enhanced light intensity are determined by the geometry of the nanolens and the incident angle, in good agreement with simulation results. This strong focusing effect of the surface nanolens is shown to significantly promote the plasmonic effect of deposited gold nanoparticles on the lens surface inlight conversion and to vaporize surrounding water to microbubbles by using low laser power. This work further demonstrates that the light redistribution by the surface nanolens in TIR enables a range of novel applications in selectively local visualization of specimens in fluorescence imaging, optical trapping of colloids from an external flow, and selective materials deposition from photoreactions.

Nano-Enabled Approaches to Chemical Imaging in Biosystems

Understanding and predicting how biosystems function require knowledge about the dynamic physicochemical environments with which they interact and alter by their presence. Yet, identifying specific components, tracking the dynamics of the system, and monitoring local environmental conditions without disrupting biosystem function present significant challenges for analytical measurements. Nanomaterials, by their very size and nature, can act as probes and interfaces to biosystems and offer solutions to some of these challenges. At the nanoscale, material properties emerge that can be exploited for localizing biomolecules and making chemical measurements at cellular and subcellular scales. Here, we review advances in chemical imaging enabled by nanoscale structures, in the use of nanoparticles as chemical and environmental probes, and in the development of micro- and nanoscale fluidic devices to define and manipulate local environments and facilitate chemical measurements of complex biosystems. Integration of these nano-enabled methods will lead to an unprecedented understanding of biosystem function.

Turning a normal microscope into a super-resolution instrument using a scanning microlens array

We report dielectric microsphere array-based optical super-resolution microscopy. A dielectric microsphere that is placed on a sample is known to generate a virtual image with resolution better than the optical diffraction limit. However, a limitation of such type of super-resolution microscopy is the restricted field-of-view, essentially limited to the central area of the microsphere-generated image. We overcame this limitation by scanning a micro-fabricated array of ordered microspheres over the sample using a customized algorithm that moved step-by-step a motorized stage, meanwhile the microscope-mounted camera was taking pictures at every step. Finally, we stitched together the extracted central parts of the virtual images that showed super-resolution into a mosaic image. We demonstrated 130 nm lateral resolution (~λ/4) and 5 × 10⁵ µm² scanned surface area using a two by one array of barium titanate glass microspheres in oil-immersion environment. Our findings may serve as a basis for widespread applications of affordable optical super-resolution microscopy.

Super-resolution imaging by metamaterial-based compressive spatial-to-spectral transformation

We present a new far-field super-resolution imaging approach called compressive spatial to spectral transformation microscopy (CSSTM). The transformation encodes the high-resolution spatial information to a spectrum through illuminating sub-diffraction-limited and wavelength-dependent patterns onto an object. The object is reconstructed from scattering spectrum measurements in the far field. The resolution of the CSSTM is mainly determined by the materials used to perform the spatial to spectral transformation. As an example, we numerically demonstrate sub-15 nm resolution by using a practically achievable Ag/SiO₂ multilayer hyperbolic metamaterial.

Plasmonic Effects of Metallic Nanoparticles on Enhancing Performance of Perovskite Solar Cells

We report systematic design and formation of plasmonic perovskite solar cells (PSCs) by integrating Au@TiO₂ core-shell nanoparticles (NPs) into porous TiO₂ and/or perovskite semiconductor capping layers. The plasmonic effects in the formed PSCs are examined. The most efficient configuration is obtained by incorporating Au@TiO₂ NPs into both the porous TiO₂ and the perovskite capping layers, which increases the power conversion efficiency (PCE) from 12.59% to 18.24%, demonstrating over 44% enhancement, compared with the reference device without the metal NPs. The PCE enhancement is mainly attributed to short-circuit current improvement. The plasmonic enhancement effects of Au@TiO₂ core-shell nanosphere photovoltaic composites are explored based on the combination of UV-vis absorption spectroscopy, external quantum efficiency (EQE), photocurrent properties, and photoluminescence (PL). The addition of Au@TiO₂ nanospheres increased the rate of exciton generation and the probability of exciton dissociation, enhancing charge separation/transfer, reducing the recombination rate, and facilitating carrier transport in the device. This study contributes to understanding of plasmonic effects in perovskite solar cells and also provides a promising approach for simultaneous photon energy and electron management.

Boosting magnetic field enhancement with radiative couplings of magnetic modes in dielectric nanostructures

Dielectric nanostructures can readily support considerable magnetic field enhancements that offer great potential applications in field enhanced spectroscopies. However, the magnetic fields of dielectric structures are usually distributed within the entire volume, which brings challenge to the further increment of the magnetic field enhancement. Here, we theoretically demonstrate that the magnetic field enhancement in dielectric nanostructures can be boosted through the radiative couplings of magnetic modes. Our concentric structure consists of a hollow disk and a ring. The disk has a magnetic dipole mode. The ring has two magnetic dipole modes that are out of phase. Strong radiative interactions between the modes on the disk and the ring can occur, which result in a net constructive coupling effect. For a lossless material with n = 3.3, a sharp peak can be obtained on the scattering spectrum of the coupled system due to the radiative interactions. The corresponding resonant magnetic field enhancement at the disk center reaches 96 times. This enhancement is about 7 times higher than that of an individual disk. The structure with a lossy material Si is also considered, where radiative couplings and boosted magnetic field can also be obtained. Our research reveals the strong radiative mode couplings in dielectric structures and is important for furthering our understanding on the light-matter interactions at the nanoscale.

Graphene-based near-field optical microscopy: high-resolution imaging using reconfigurable gratings

High-resolution and fast-paced optical microscopy is a requirement for current trends in biotechnology and materials industry. The most reliable and adaptable technique so far to obtain higher resolution than conventional microscopy is near-field scanning optical microscopy (NSOM), which suffers from a slow-paced nature. Stemming from the principles of diffraction imaging, we present fast-paced graphene-based scanning-free wide-field optical microscopy that provides image resolution that competes with NSOM. Instead of spatial scanning of a sharp tip, we utilize the active reconfigurable nature of graphene's surface conductivity to vary the diffraction properties of a planar digitized atomically thin graphene sheet placed in the near field of an object. Scattered light through various realizations of gratings is collected at the far-field distance and postprocessed using a transmission function of surface gratings developed on the principles of rigorous coupled wave analysis. We demonstrate image resolutions of the order of λ₀/16 using computational measurements through binary graphene gratings and numerical postprocessing. We also present an optimization scheme based on the genetic algorithm to predesign the unit cell structure of the gratings to minimize the complexity of postprocessing methods. We present and compare the imaging performance and noise tolerance of both grating types. While the results presented in this article are at terahertz frequencies (λ₀=10  μm), where graphene is highly plasmonic, the proposed microscopy principle can be readily extended to any frequency regime subject to the availability of tunable materials.

Superlensing microscope objective lens

Conventional microscope objective lenses are diffraction limited; they cannot resolve subdiffraction features of a size smaller than 250-300 nm under white lighting condition. New innovations are required to overcome this limitation. In this paper, we propose and demonstrate a new superlensing objective lens that possesses a resolution of 100 nm, which is a two-times resolution improvement over conventional objectives. This is accomplished by integrating a conventional microscope objective lens with a superlensing microsphere lens using a customized lens adaptor. The new objective lens was successfully demonstrated for label-free super-resolution imaging of 100 nm features in engineering and biological samples, including a Blu-ray disk sample and adenoviruses. Our work opens a new door to develop a generic optical superlens, which may transform the field of optical microscopy and imaging.

Efficient perovskite solar cells by combination use of Au nanoparticles and insulating metal oxide

Achieving high open-circuit voltage and high short-circuit current density simultaneously is a big challenge in the development of highly efficient perovskite solar cells, due to the complex excitonic nature of hybrid organic-inorganic semiconductors. Herein, we developed a facile and effective method to fabricate efficient plasmonic PSC devices. The solar cells were prepared by incorporating Au nanoparticles (NPs) into mesoporous TiO₂ films and depositing a MgO passivation film on the Au NP-modified mesoporous titania via wet spinning and pyrolysis of magnesium salt. The PSCs obtained by combining Au NPs and MgO demonstrated a high power conversion efficiency of 16.1%, with both a high open-circuit voltage of 1.09 V and a high short-circuit current density of 21.76 mA cm^-2. The device achieved a 34.2% improvement in the power conversion efficiency compared with a device based on pure TiO₂. Moreover, a significant improvement of the UV stability in the perovskite solar cell was achieved due to the combined use of Au NPs and insulating MgO. The fundamental optics and physics behind the regulation of energy flow in the perovskite solar cell and the concept of using Au NPs and MgO to improve the device performance were explored. The results indicate that the combined use of Au NPs and a MgO passivation film is an effective way to design high performance and high stability organic-inorganic perovskite photovoltaic materials.