Drug classification with a spectral barcode obtained with a smartphone Raman spectrometer.

Measuring, recording and analyzing spectral information of materials as its unique finger print using a ubiquitous smartphone has been desired by scientists and consumers. We demonstrated it as drug classification by chemical components with smartphone Raman spectrometer. The Raman spectrometer is based on the CMOS image sensor of the smartphone with a periodic array of band pass filters, capturing 2D Raman spectral intensity map, newly defined as spectral barcode in this work. Here we show 11 major components of drugs are classified with high accuracy, 99.0%, with the aid of convolutional neural network (CNN). The beneficial of spectral barcodes is that even brand name of drug is distinguishable and major component of unknown drugs can be identified. Combining spectral barcode with information obtained by red, green and blue (RGB) imaging system or applying image recognition techniques, this inherent property based labeling system will facilitate fundamental research and business opportunities.

All-optical control of high-purity trions in nanoscale waveguide.

The generation of high-purity localized trions, dynamic exciton-trion interconversion, and their spatial modulation in two-dimensional (2D) semiconductors are building blocks for the realization of trion-based optoelectronic devices. Here, we present a method for the all-optical control of the exciton-to-trion conversion process and its spatial distributions in a MoS2 monolayer. We induce a nanoscale strain gradient in a 2D crystal transferred on a lateral metal-insulator-metal (MIM) waveguide and exploit propagating surface plasmon polaritons (SPPs) to localize hot electrons. These significantly increase the electrons and efficiently funnel excitons in the lateral MIM waveguide, facilitating complete exciton-to-trion conversion even at ambient conditions. Additionally, we modulate the SPP mode using adaptive wavefront shaping, enabling all-optical control of the exciton-to-trion conversion rate and trion distribution in a reversible manner. Our work provides a platform for harnessing excitonic quasiparticles efficiently in the form of trions at ambient conditions, enabling high-efficiency photoconversion.

Glasswing-Butterfly-Inspired Multifunctional Scleral Lens and Smartphone Raman Spectrometer for Point-of-Care Tear Biomarker Analysis.

Augmenting contact lenses with sensing capabilities requires incorporating multiple functionalities within a diminutive device. Inspired by multifunctional biophotonic nanostructures of glasswing butterflies, a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities is reported. When used in conjunction with a smartphone-integrated Raman spectrometer, the feasibility of point-of-care applications is demonstrated. The bioinspired nanostructures made on parylene films are mounted on the anterior and posterior side of a scleral lens to create a nanostructured lens. Compared to unstructured parylene, nanostructured parylene minimizes glare by 4.3-fold at large viewing angles up to 80o . When mounted on a scleral lens, the nanostructures block 2.8-fold more ultraviolet (UVA) light while offering 1.1-fold improved transmission in the visible regime. Furthermore, the nanostructures exhibit potent bactericidal activity against Escherichia coli, killing 89% of tested bacteria within 4 h. The same nanostructures, when gold-coated, are used to perform rapid label-free multiplex detection of lysozyme and lactoferrin, the protein biomarkers of the chronic dry eye disease, in whole human tears using drop-coating deposition Raman spectroscopy. The detection of both proteins in whole human tear samples from different subjects using the nanostructured lens produced excellent correlation with commercial enzyme-based assays while simultaneously displaying a 1.5-fold lower standard deviation.

Structurally engineered colloidal quantum dot phosphor using TiO2 photonic crystal backbone.

Photonic crystal (PhC) phosphor, in which the phosphor material is periodically modulated for an enhancement in color-conversion efficiency via resonant absorption of excitation photons, is a paradigm-shifting structural phosphor platform. Two-dimensional (2D) square-lattice PhC phosphor is currently considered the most advanced platform because of not only its high efficiency, but also its immunity to excitation polarization. In the present study, two major modifications are made to further improve the performance of the 2D PhC phosphor: increasing the refractive index contrast and planarizing the surface. The index contrast is improved by replacing the PhC backbone material with TiO2 whereas the surface planarization is achieved by removing excessive colloidal quantum dots from the surface. In comparison with the reference phosphor, the upgraded PhC phosphor exhibits ~59 times enhanced absorption (in simulations) and ~7 times enhanced emission (in experiments), both of which are unprecedentedly high. Our results not only brighten the viability and applicability of the PhC phosphor but also spur the phosphor development through structural engineering of phosphor materials.

What drives the use of wearable healthcare devices? A cross-country comparison between the US and Korea.

Objective: Given the rapid growth of the wearable healthcare device market, we examined the associations among health-related and technology-related characteristics of using wearable healthcare devices and demonstrated how the associations differ between the US and Korean users. Methods: Online self-administered surveys were conducted with 4098 participants (3035 in the US and 1063 in Korea) who were recruited through two online survey service providers based on quota sampling. The primary outcome was the use of wearable healthcare devices. Seven health-related, two technology-related, and five socio-demographic factors were included as explanatory variables. Binary logistic regression analyses and a Chow test were conducted. Results: The health-related characteristics that were significantly associated with using wearable healthcare devices included disease-related worries (ß = 0.11**), health information seeking (ß = 0.26***), physical activity (ß = 0.62***), and health-related expenditures ($50-$199, ß = 0.38***; $200 or more, ß = 0.56***). Hedonic (ß = 0.33***), social (ß = 0.31***), and cognitive innovativeness (ß = 0.14*) also exhibited positive relationships. Younger, higher earner, and individuals with a child were more likely to use wearable healthcare devices. However, for Korean users, several associations disappeared including health information seeking, hedonic and social innovativeness, age, and household income. Conclusions: Key drivers of using wearable healthcare devices include greater concern about a specific illness, active engagement in health-promoting behaviors, and hedonic and social motivation to adopt new technologies. However, more country-specific considerations are needed in future studies to identify the main benefits for target markets.

Drift-dominant exciton funneling and trion conversion in 2D semiconductors on the nanogap.

Understanding and controlling the nanoscale transport of excitonic quasiparticles in atomically thin two-dimensional (2D) semiconductors are crucial to produce highly efficient nano-excitonic devices. Here, we present a nanogap device to selectively confine excitons or trions of 2D transition metal dichalcogenides at the nanoscale, facilitated by the drift-dominant exciton funneling into the strain-induced local spot. We investigate the spatiospectral characteristics of the funneled excitons in a WSe2 monolayer (ML) and converted trions in a MoS2 ML using hyperspectral tip-enhanced photoluminescence imaging with <15-nm spatial resolution. In addition, we dynamically control the exciton funneling and trion conversion rate by the gigapascal-scale tip pressure engineering. Through a drift-diffusion model, we confirm an exciton funneling efficiency of ∼25% with a significantly low strain threshold (∼0.1%), which sufficiently exceeds the efficiency of ∼3% in previous studies. This work provides a previously unexplored strategy to facilitate efficient exciton transport and trion conversion of 2D semiconductor devices.

A Tactile-Pattern-Integrated Sensing Window for More Consistent Photoplethysmography (PPG) Measurements.

We have demonstrated a tactile-pattern-integrated sensing window for more consistent photoplethysmogram (PPG) measurements. The pattern is composed of two tiny bumps that measure 500µm in diameter and 300µm in height and allow users to position their finger pulps more consistently on the sensing window over different measurement occasions, simply by following their tactile sensation. We experimentally compared the tactile pattern window to a flat window (without any bumps) for 5 test subjects and found that the sensing window with the tactile pattern significantly helped users obtain more consistent PPG signals than the flat window (p < 0.01).The use of PPG sensors in mobile phones and wearable watches have been limited to the measurements of heart rates and blood oxygen saturation in spite of widely-spread efforts to expand their applications. This is due to the fluctuations observed between measurements which largely originate from inconsistent placement of fingers on the sensing windows. The integrated tactile pattern could provide consistent and accurate measurements and lead to more successful commercialization of diverse PPG-based mobile healthcare services.

Landau-damping-induced limits to light-matter interactions in sub-10-nm planar plasmonic nanocavities.

Landau damping has previously been shown to be the dominant nonlocal effect in sub-10nm plasmonic nanostructures, although its effects on the performance of plasmonic nanocavities are still poorly understood. In this work, the effects of Landau damping in sub-10-nm planar plasmonic nanocavities are analyzed theoretically, and it is shown that while Landau damping does not affect the confinement of the cavity modes, it decreases the quality factor 10-fold due to the introduction of extra loss for sub-10nm gap sizes. As compared to purely classical models, this results in a suppression in the Purcell factor by 10 fold, the spontaneous emission rate by almost two orders of magnitude, and the required oscillator strength to achieve strong light-matter coupling by two orders of magnitude as the gap is reduced to ∼0.5nm. Therefore, it is crucial to consider Landau damping in plasmonic-nanocavity design because it breaks the classical norm of achieving higher light-matter interaction strength in sub-10-nm gap-plasmon nanocavities.

High sensitivity bolometers based on metal nanoantenna dimers with a nanogap filled with vanadium dioxide.

One critical factor for bolometer sensitivity is efficient electromagnetic heating of thermistor materials, which plasmonic nanogap structures can provide through the electric field enhancement. In this report, using finite element method simulation, electromagnetic heating of nanorod dimer antennas with a nanogap filled with vanadium dioxide (VO2) was studied for long-wavelength infrared detection. Because VO2 is a thermistor material, the electrical resistance between the two dimer ends depends on the dimer's temperature. The simulation results show that, due to the high heating ability of the nanogap, the temperature rise is several times higher than expected from the areal coverage. This excellent performance is observed over various nanorod lengths and gap widths, ensuring wavelength tunability and ultrafast operating speed, thereby making the dimer structures a promising candidate for high sensitivity bolometers.

All-solid-state spatial light modulator with independent phase and amplitude control for three-dimensional LiDAR applications.

Spatial light modulators are essential optical elements in applications that require the ability to regulate the amplitude, phase and polarization of light, such as digital holography, optical communications and biomedical imaging. With the push towards miniaturization of optical components, static metasurfaces are used as competent alternatives. These evolved to active metasurfaces in which light-wavefront manipulation can be done in a time-dependent fashion. The active metasurfaces reported so far, however, still show incomplete phase modulation (below 360°). Here we present an all-solid-state, electrically tunable and reflective metasurface array that can generate a specific phase or a continuous sweep between 0 and 360° at an estimated rate of 5.4 MHz while independently adjusting the amplitude. The metasurface features 550 individually addressable nanoresonators in a 250 × 250 µm2 area with no micromechanical elements or liquid crystals. A key feature of our design is the presence of two independent control parameters (top and bottom gate voltages) in each nanoresonator, which are used to adjust the real and imaginary parts of the reflection coefficient independently. To demonstrate this array's use in light detection and ranging, we performed a three-dimensional depth scan of an emulated street scene that consisted of a model car and a human figure up to a distance of 4.7 m.

Subwavelength pixelated CMOS color sensors based on anti-Hermitian metasurface.

The demand for essential pixel components with ever-decreasing size and enhanced performance is central to current optoelectronic applications, including imaging, sensing, photovoltaics and communications. The size of the pixels, however, are severely limited by the fundamental constraints of lightwave diffraction. Current development using transmissive filters and planar absorbing layers can shrink the pixel size, yet there are two major issues, optical and electrical crosstalk, that need to be addressed when the pixel dimension approaches wavelength scale. All these fundamental constraints preclude the continual reduction of pixel dimensions and enhanced performance. Here we demonstrate subwavelength scale color pixels in a CMOS compatible platform based on anti-Hermitian metasurfaces. In stark contrast to conventional pixels, spectral filtering is achieved through structural color rather than transmissive filters leading to simultaneously high color purity and quantum efficiency. As a result, this subwavelength anti-Hermitian metasurface sensor, over 28,000 pixels, is able to sort three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration opens a new door to sub-wavelength pixelated CMOS sensors and promises future high-performance optoelectronic systems.

Overcoming evanescent field decay using 3D-tapered nanocavities for on-chip targeted molecular analysis.

Enhancement of optical emission on plasmonic nanostructures is intrinsically limited by the distance between the emitter and nanostructure surface, owing to a tightly-confined and exponentially-decaying electromagnetic field. This fundamental limitation prevents efficient application of plasmonic fluorescence enhancement for diversely-sized molecular assemblies. We demonstrate a three-dimensionally-tapered gap plasmon nanocavity that overcomes this fundamental limitation through near-homogeneous yet powerful volumetric confinement of electromagnetic field inside an open-access nanotip. The 3D-tapered device provides fluorescence enhancement factors close to 2200 uniformly for various molecular assemblies ranging from few angstroms to 20 nanometers in size. Furthermore, our nanostructure allows detection of low concentration (10 pM) biomarkers as well as specific capture of single antibody molecules at the nanocavity tip for high resolution molecular binding analysis. Overcoming molecule position-derived large variations in plasmonic enhancement can propel widespread application of this technique for sensitive detection and analysis of complex molecular assemblies at or near single molecule resolution.

Bioinspired Disordered Flexible Metasurfaces for Human Tear Analysis Using Broadband Surface-Enhanced Raman Scattering.

Flexible surface-enhanced Raman scattering (SERS) has received attention as a means to move SERS-based broadband biosensing from bench to bedside. However, traditional flexible periodic nano-arrangements with sharp plasmonic resonances or their random counterparts with spatially varying uncontrollable enhancements are not reliable for practical broadband biosensing. Here, we report bioinspired quasi-(dis)ordered nanostructures presenting a broadband yet tunable application-specific SERS enhancement profile. Using simple, scalable biomimetic fabrication, we create a flexible metasurface (flex-MS) of quasi-(dis)ordered metal-insulator-metal (MIM) nanostructures with spectrally variable, yet spatially controlled electromagnetic hotspots. The MIM is designed to simultaneously localize the electromagnetic signal and block background Raman signals from the underlying polymeric substrate-an inherent problem of flexible SERS. We elucidate the effect of quasi-(dis)ordering on broadband tunable SERS enhancement and employ the flex-MS in a practical broadband SERS demonstration to detect human tear uric acid within its physiological concentration range (25-150 µM). The performance of the flex-MS toward noninvasively detecting whole human tear uric acid levels ex vivo is in good agreement with a commercial enzyme-based assay.

Investigation on energy bandgap states of amorphous SiZnSnO thin films.

The variation in energy bandgaps of amorphous oxide semiconducting SiZnSnO (a-SZTO) has been investigated by controlling the oxygen partial pressure (Op). The systematic change in Op during deposition has been used to control the electrical characteristics and energy bandgap of a-SZTO. As Op increased, the electrical properties degraded, while the energy bandgap increased systematically. This is mainly due to the change in the oxygen vacancy inside the a-SZTO thin film by controlling Op. Changes in oxygen vacancies have been observed by using X-ray photoelectron spectroscopy (XPS) and investigated by analyzing the variation in density of states (DOS) inside the energy bandgaps. In addition, energy bandgap parameters, such as valence band level, Fermi level, and energy bandgap, were extracted by using ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and high-resolution electron energy loss spectroscopy. As a result, it was confirmed that the difference between the conduction band minimum and the Fermi level in the energy bandgap increased systematically as Op increases. This shows good agreement with the measured results of XPS and DOS analyses.

Fabry-Pérot optical sensor and portable detector for monitoring high-resolution ocular hemodynamics.

Our understanding of ocular hemodynamics and its role in ophthalmic disease progression remains unclear due to the shortcomings of precise and on-demand biomedical sensing technologies. Here, we report high-resolution in vivo assessment of ocular hemodynamics using a Fabry-Pérot cavity-based micro-optical sensor and a portable optical detector. The designed optical system is capable of measuring both static intraocular pressure and dynamic ocular pulsation profiles in parallel. Through a dynamic intensity variation analysis method which improves sensing resolution by 3-4 folds, our system is able to extract systolic/diastolic phases from a single ocular pulsation profile. Using a portable detector, we performed in vivo studies on rabbits and verified that ophthalmic parameters obtained from our optical system closely match with traditional techniques such as tonometry, electrocardiography, and photo-plethysmography.

Aluminum Metasurface with Hybrid Multipolar Plasmons for 1000-Fold Broadband Visible Fluorescence Enhancement and Multiplexed Biosensing.

Aluminum (Al)-based nanoantennae traditionally suffer from weak plasmonic performance in the visible range, necessitating the application of more expensive noble metal substrates for rapidly expanding biosensing opportunities. We introduce a metasurface comprising Al nanoantennae of nanodisks-in-cavities that generate hybrid multipolar lossless plasmonic modes to strongly enhance local electromagnetic fields and increase the coupled emitter's local density of states throughout the visible regime. This results in highly efficient electromagnetic field confinement in visible wavelengths by these nanoantennae, favoring real-world plasmonic applications of Al over other noble metals. Additionally, we demonstrate spontaneous localization and concentration of target molecules at metasurface hotspots, leading to further improved on-chip detection sensitivity and a broadband fluorescence-enhancement factor above 1000 for visible wavelengths with respect to glass chips commonly used in bioassays. Using the metasurface and a multiplexing technique involving three visible wavelengths, we successfully detected three biomarkers, insulin, vascular endothelial growth factor, and thrombin relevant to diabetes, ocular and cardiovascular diseases, respectively, in a single 10 µL droplet containing only 1 fmol of each biomarker.

Enhanced broadband fluorescence detection of nucleic acids using multipolar gap-plasmons on biomimetic Au metasurfaces.

Recent studies on metal-insulator-metal-based plasmonic antennas have shown that emitters could couple with higher-order gap-plasmon modes in sub-10-nm gaps to overcome quenching. However, these gaps are often physically inaccessible for functionalization and are not scalably manufacturable. Here, using a simple biomimetic batch-fabrication, a plasmonic metasurface is created consisting of closely-coupled nanodisks and nanoholes in a metal-insulator-metal arrangement. The quadrupolar mode of this system exhibits strong broadband resonance in the visible-near-infrared regime with minimal absorptive losses and effectively supresses quenching, making it highly suitable for broadband plasmon-enhanced fluorescence. Functionalizing the accessible insulator nanogap, analytes are selectively immobilized onto the plasmonic hotspot enabling highly-localized detection. Sensing the streptavidin-biotin complex, a 91-, 288-, 403- and 501-fold fluorescence enhancement is observed for Alexa Fluor 555, 647, 750 and 790, respectively. Finally, the detection of single-stranded DNA (gag, CD4 and CCR5) analogues of genes studied in the pathogenesis of HIV-1 between 10 pM-10 µM concentrations and then CD4 mRNA in the lysate of transiently-transfected cells with a 5.4-fold increase in fluorescence intensity relative to an untransfected control is demonstrated. This outcome promises the use of biomimetic Au metasurfaces as platforms for robust detection of low-abundance nucleic acids.

Glucose Sensing Using Surface-Enhanced Raman-Mode Constraining.

Diabetes mellitus is a chronic disease, and its management focuses on monitoring and lowering a patient's glucose level to prevent further complications. By tracking the glucose-induced shift in the surface-enhanced Raman-scattering (SERS) emission of mercaptophenylboronic acid (MPBA), we have demonstrated fast and continuous glucose sensing in the physiologically relevant range from 0.1 to 30 mM and verified the underlying mechanism using numerical simulations. Bonding of glucose to MPBA suppresses the "breathing" mode of MPBA at 1071 cm-1 and energizes the constrained-bending mode at 1084 cm-1, causing the dominant peak to shift from 1071 to 1084 cm-1. MPBA-glucose bonding is also reversible, allowing continuous tracking of ambient glucose concentrations, and the MPBA-coated substrates showed very stable performance over a 30 day period, making the approach promising for long-term continuous glucose monitoring. Using Raman-mode-constrained, miniaturized SERS implants, we also successfully demonstrated intraocular glucose measurements in six ex vivo rabbit eyes within ±0.5 mM of readings obtained using a commercial glucose sensor.