Poly(catecholamine) coated CsPbBr3 perovskite microlasers: lasing in water and biofunctionalization.

Lead halide perovskite (LHP) is a promising material for various optoelectronic applications. Surface coating on particles is a common strategy to improve their functionality and environmental stability, but LHP is not amenable to most coating chemistries because of its intrinsic weakness against polar solvents. Here, we describe a novel method of synthesizing LHP microlasers in a super-saturated polar solvent using sonochemistry and applying various functional coatings on individual microlasers in situ. We synthesize cesium lead bromine perovskite (CsPbBr3) microcrystals capped with organic poly-norepinephrine (pNE) layers. The catechol group of pNE coordinates to bromine-deficient lead atoms, forming a defect-passivating and diffusion-blocking shell. The pNE layer enhances the material lifetime of CsPbBr3 in water by 2,000-folds, enabling bright luminescence and lasing from single microcrystals in water. Furthermore, the pNE shell permits biofunctionalization with proteins, small molecules, and lipid bilayers. Luminescence from CsPbBr3 microcrystals is sustained in water over 1 hour and observed in live cells. The functionalization method may enable new applications of LHP laser particles in water-rich environments.

Compact Quantum-Dot Microbeads with Sub-Nanometer Emission Linewidth.

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Here, we demonstrate microbeads capable of generating single-peak laser emission with a sub-nanometer linewidth. The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single-mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 µm in the air. Sub-nm lasing emission is maintained even inside high-index surroundings, such as organic solvents and biological tissues. Feasibility of intracellular tagging and multi-color imaging in vivo is demonstrated.

Droplet microfluidic generation of a million optical microparticle barcodes.

Micron-scale barcode particles enable labelling of small objects. Here, we demonstrate high-throughput barcode fabrication inside a microfluidic chip that can embed multiple, dye-doped high quality-factor whispering gallery mode cavities inside aqueous droplets at kilohertz rates. These droplets are then cured to form polyacrylamide hydrogel beads as small as 30 µm in diameter. Optical resonance spectra of the embedded cavities provide the hydrogels with unique barcodes with their diversity combinatorically scaled with the number of embedded cavities. Using 3 cavities per hydrogel, we obtain approximately one million uniquely identifiable, optically readable barcode microparticles.

Plasmonic metasurface for simultaneous detection of polarization and spectrum.

We present a new plasmonic metasurface for simultaneous detection of polarization and spectrum of incident light. The demonstrated metasurface is a rationally designed cluster of artificial atoms that are engineered to exhibit polarization and wavelength-selective optical transmission. The fundamental building block of this structure is periodically coupled subwavelength aperture arrays with different orientations and lattice constants. When integrated with pixelated photodetectors, the metasurface can be used to measure the polarization and spectral information of an optical input. In this Letter, simultaneous detection of the polarization and spectrum of polarized light was experimentally demonstrated by analyzing the transmitted intensity distribution through the metasurface. The demonstrated metasurface offers great potential for many applications, such as polarimetric multispectral imaging and polarization-division multiplexing in optical communications.

Laser Particle Stimulated Emission Microscopy.

We introduce an optical microscopy technique that utilizes micro- or nanolasers embedded in a sample as imaging probes. The narrow spectra and nonlinear power dependence of stimulated emission from the laser particles yield optical sectioning, subdiffraction resolution, and low out-of-focus background. A proof of concept is demonstrated using perovskite nanowires.

Complex index of refraction estimation from degree of polarization with diffuse scattering consideration.

The estimation of the refractive index from optical scattering off a target's surface is an important task for remote sensing applications. Optical polarimetry is an approach that shows promise for refractive index estimation. However, this estimation often relies on polarimetric models that are limited to specular targets involving single surface scattering. Here, an analytic model is developed for the degree of polarization (DOP) associated with reflection from a rough surface that includes the effect of diffuse scattering. A multiplicative factor is derived to account for the diffuse component and evaluation of the model indicates that diffuse scattering can significantly affect the DOP values. The scattering model is used in a new approach for refractive index estimation from a series of DOP values that involves jointly estimating n, k, and ρ(d)with a nonlinear equation solver. The approach is shown to work well with simulation data and additive noise. When applied to laboratory-measured DOP values, the approach produces significantly improved index estimation results relative to reference values.

Defect-assisted plasmonic crystal sensor.

We demonstrate enhanced sensitivity of a nanostructured plasmonic sensor that utilizes resonance in intentional structural defects within a plasmonic crystal. The measured sensitivity of the fabricated nanosensor is ~500 nm/RIU showing improvement over traditional nanohole array sensors. Furthermore, the defects provide an additional design parameter to increase sensitivity by engineering plasmon lifetime.

Quantitative phase imaging techniques for the study of cell pathophysiology: from principles to applications.

A cellular-level study of the pathophysiology is crucial for understanding the mechanisms behind human diseases. Recent advances in quantitative phase imaging (QPI) techniques show promises for the cellular-level understanding of the pathophysiology of diseases. To provide important insight on how the QPI techniques potentially improve the study of cell pathophysiology, here we present the principles of QPI and highlight some of the recent applications of QPI ranging from cell homeostasis to infectious diseases and cancer.

Ultrasmall InGa(As)P Dielectric and Plasmonic Nanolasers.

Nanolasers have great potential for both on-chip light sources and optical barcoding particles. We demonstrate ultrasmall InGaP and InGaAsP disk lasers with diameters down to 360 nm (198 nm in height) in the red spectral range. Optically pumped, room-temperature, single-mode lasing was achieved from both disk-on-pillar and isolated particles. When isolated disks were placed on gold, plasmon polariton lasing was obtained with Purcell-enhanced stimulated emission. UV lithography and plasma ashing enabled wafer-scale fabrication of nanodisks with an intended random size variation. Silica-coated nanodisk particles generated stable subnanometer spectra from within biological cells across an 80 nm bandwidth from 635 to 715 nm.

A periodically coupled plasmon nanostructure for refractive index sensing.

We present unique characteristics of subwavelength surface plasmon polaritons in a periodically coupled nanowell structure. The nanowell structure offers high quality internal surface plasmon resonance for sensing applications. Calculated FWHM of the transmission peak is 6 nm and the optical transmission is close to 100% at the resonant wavelength of 815.8 nm. The highly concentrated polaritons in the nanowell are sensitive to surface changes providing a sensitivity of 4800% RIU(-1) for optical sensing applications.

Submicrometer perovskite plasmonic lasers at room temperature.

Plasmonic lasers attracted interest for their ability to generate coherent light in mode volume smaller than the diffraction limit of photonic lasers. While nanoscale devices in one or two dimensions were demonstrated, it has been difficult to achieve plasmonic lasing with submicrometer cavities in all three dimensions. Here, we demonstrate submicrometer-sized, plasmonic lasers using cesium-lead-bromide perovskite (CsPbBr3) crystals, as small as 0.58 µm by 0.56 µm by 0.32 µm (cuboid) and 0.79 µm by 0.66 µm by 0.18 µm (plate), on polymer-coated gold substrates at room temperature. Our experimental and simulation data obtained from more than 100 plasmonic and photonic devices showed that enhanced optical gain by the Purcell effect, large spontaneous emission factor, and high group index are key elements to efficient plasmonic lasing. The results shed light on the three-dimensional miniaturization of plasmonic lasers.

Structure and optical properties of perovskite-embedded dual-phase microcrystals synthesized by sonochemistry.

Cesium lead halide perovskite (CsPbX3, X=Cl, Br, I) nanocrystals embedded in Cs4PbX6 or CsPb2X5 matrices have received interests due to their excellent optical properties. However, their precise endotaxial structures are not known, and the origin of photoluminescence remains controversial. Here we report a sonochemistry technique that allowed us to synthesize high-quality CsPbBr3-based microcrystals in all ternary phases, simply by adjusting precursor concentrations in a polar aprotic solvent, N,N-dimethylformamide. The microcrystals with diverse morphologies enabled us to visualize the lattice alignments in the dual-phase composites and confirm CsPbBr3 nanocrystals being the photoluminescent sites. We demonstrate high solid-state quantum yield of >40% in Cs4PbBr6/CsPbBr3 and lasing of CsPbBr3 microcrystals as small as 2 µm in size. Real-time optical analysis of the reaction solutions provides insights into the formation and phase transformation of different CsPbBr3-based microcrystals.

Conformal Coating of Freestanding Particles by Vapor-Phase Infiltration.

A novel atomic layer method for encapsulating individual micro- and nano-particles with thin (sub-10-nm) dielectric films is presented. This method leverages the diffusion of vapor-phase precursors through an underlying inert polymer film to achieve growth of a metal oxide film on all sides of the particle simultaneously; even on the side that is in contact with the substrate. Crucially, the deposition is performed on stationary particles and does not require an agitation mechanism or a special reaction chamber. Here, conformal coatings of alumina are shown to improve stability in aqueous environments for two optically-relevant particles: compound semiconductor laser microparticles and lead halide perovskite nanocrystals.

Long-Term Mosquito culture with SkitoSnack, an artificial blood meal replacement.

The reliance on blood is a limiting factor for mass rearing of mosquitoes for Sterile-Insect-Technique (SIT) and other mosquito-based control strategies. To solve this problem, we have developed SkitoSnack, a formulated diet for Aedes aegypti (L) mosquitoes, as an alternative for vertebrate blood. Here we addressed the question if long-term yellow fever mosquito culture with SkitoSnack resulted in changed life history traits and fitness of the offspring compared to blood-raised mosquitoes. We also explored if SkitoSnack is suitable to raise Asian tiger mosquitos, Aedes albopictus (L.), and the human bed bug, Cimex lectularius (L). We measured life history traits for 30th generation SkitoSnack-raised Ae. aegypti and 11th generation SkitoSnack-raised Ae. albopictus, and compared them with control mosquitoes raised on blood only. We compared meal preference, flight performance, and reproductive fitness in Ae. aegypti raised on SkitoSnack or blood. We also offered SkitoSnack to bed bug nymphs. We found that long-term culture with SkitoSnack resulted in mosquitoes with similar life history traits compared to bovine blood-raised mosquitoes in both species we studied. Also, Ae. aegypti mosquitoes raised on SkitoSnack had similar flight performance compared to blood raised mosquitoes, were still strongly attracted by human smell and had equal mating success. Minimal feeding occurred in bed bugs. Our results suggest that long-term culture with the blood-meal replacement SkitoSnack results in healthy, fit mosquitoes. Therefore, artificial diets like SkitoSnack can be considered as a viable alternative for vertebrate blood in laboratory mosquito culture as well as for mosquito mass production for Sterile-Insect-Technique mosquito control interventions. SkitoSnack was not suitable to induce engorgement of bed bugs.

Chip-scale hybrid optical sensing systems using digital signal processing.

We propose a novel hybrid optical sensing system for standalone, chip-scale sensing applications. The hybrid optical sensing system detects any spectral shift of the microresonator sensor output by estimating the effective refractive index using maximum likelihood estimation. The performance evaluation of the proposed hybrid sensing system in the Gaussian-noise dominant environment shows excellent estimation accuracy. This innovative approach allows fully functional integrated hybrid sensing systems, offering great potential in various chip-scale sensing applications.

Spatially and spectrally resolved orbital angular momentum interactions in plasmonic vortex generators.

Understanding the near-field electromagnetic interactions that produce optical orbital angular momentum (OAM) is crucial for integrating twisted light into nanotechnology. Here, we examine the cathodoluminescence (CL) of plasmonic vortices carrying OAM generated in spiral nanostructures. The nanospiral geometry defines a photonic local density of states that is sampled by the electron probe in a scanning transmission electron microscope (STEM), thus accessing the optical response of the plasmonic vortex with high spatial and spectral resolution. We map the full spectral dispersion of the plasmonic vortex in spiral structures designed to yield increasing topological charge. Additionally, we fabricate nested nanospirals and demonstrate that OAM from one nanospiral can be coupled to the nested nanospiral, resulting in enhanced luminescence in concentric spirals of like handedness with respect to concentric spirals of opposite handedness. The results illustrate the potential for generating and coupling plasmonic vortices in chiral nanostructures for sensitive detection and manipulation of optical OAM.

Apodized SCISSORs for filtering and switching.

This paper presents 1550-nm simulation results on the waveguided silicon-on-insulator four-port optical filtering and switching devices known as "SCISSOR" (an in-line array of microring resonators wherein each ring is coupled to two bus waveguides). We optimized the array number, the ring-bus coupling and the inter-ring spacing in order to obtain "rectangular" filter-passband shapes that have not heretofore been reported in the resonant-optics literature. We were able to engineer a box-like bandpass whose wavelength width could be anywhere from 5 to 50 % of the free spectral range (FSR). We then performed ring-bus apodization of the array that increased side-lobe suppression on the main filter band and widened the band. By reducing the FSR to 2.51 nm with increased ring diameter, we also showed that complete, high-extinction 2 x 2 optical switching is attained when the effective index of each ring in the group is changed by 2 x 10(-3), giving 1.02-nm shift of the 0.77-nm passband. Tunable filtering, sensing, reconfigurable add/drop and wavelength-division demultiplexing is offered in addition to switching.

Interferometric microring-resonant 2 x 2 optical switches.

We present modeling and simulation results on a new family of waveguided interferometric 2 x 2 optical routing switches actuated by electro-optic or thermo-optic or all-optical control. Two pairs of coupled microring resonators provide two 3dB coupling regions within a compact Mach-Zehnder geometry. An index perturbation (delta)n of 2 x 10(-3) is sufficient to produce 100% 2 x 2 switching. This perturbation can be applied to one arm of the MZI or to the four rings in the device or to an additional ring that is coupled to one arm. We find that push-pull control is effective for switching: for example, when carriers are injected in one region and depleted in a corresponding second region. An optical transfer-matrix technique is employed to determine the electromagnetic response (the 1550-nm switching characteristics) of the three device-types. Microdisks can be employed instead of microrings, if desired.

Chip-scale sensor system integration for portable health monitoring.

The revolution in integrated circuits over the past 50 yr has produced inexpensive computing and communications systems that are powerful and portable. The technologies for these integrated chip-scale sensing systems, which will be miniature, lightweight, and portable, are emerging with the integration of sensors with electronics, optical systems, micromachines, microfluidics, and the integration of chemical and biological materials (soft/wet material integration with traditional dry/hard semiconductor materials). Hence, we stand at a threshold for health monitoring technology that promises to provide wearable biochemical sensing systems that are comfortable, inauspicious, wireless, and battery-operated, yet that continuously monitor health status, and can transmit compressed data signals at regular intervals, or alarm conditions immediately. In this paper, we explore recent results in chip-scale sensor integration technology for health monitoring. The development of inexpensive chip-scale biochemical optical sensors, such as microresonators, that are customizable for high sensitivity coupled with rapid prototyping will be discussed. Ground-breaking work in the integration of chip-scale optical systems to support these optical sensors will be highlighted, and the development of inexpensive Si complementary metal-oxide semiconductor circuitry (which makes up the vast majority of computational systems today) for signal processing and wireless communication with local receivers that lie directly on the chip-scale sensor head itself will be examined.

Art on the Nanoscale and Beyond.

Methods of forming and patterning materials at the nano- and microscales are finding increased use as a medium of artistic expression, and as a vehicle for communicating scientific advances to a broader audience. While sharing many attributes of other art forms, miniaturized art enables the direct engagement of sensory aspects such as sight and touch for materials and structures that are otherwise invisible to the eye. The historical uses of nano-/microscale materials and imaging techniques in arts and sciences are presented. The motivations to create artwork at small scales are discussed, and representations in scientific literature and exhibitions are explored. Examples are presented using semiconductors, microfluidics, and nanomaterials as the artistic media; these utilized techniques including micromachining, focused ion beam milling, two-photon polymerization, and bottom-up nanostructure growth. Finally, the technological factors that limit the implementation of artwork at miniature scales are identified, and potential future directions are discussed. As research marches toward even smaller length scales, innovative and engaging visualizations and artistic endeavors will have growing implications on education, communication, policy making, media activism, and public perception of science and technology.