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When exposed to different relative humidities (RHs), the optical properties of atmospheric aerosols will change because of changes in the aerosol particle size and complex refractive index (RI), which will affect haze formation and global climate change. The potential contributions of ultrafine particles to the atmospheric optical characteristics and to haze spreading cannot be ignored because of their high particle number concentrations and strong diffusibility; measurement of the optical properties of wet ultrafine particles is thus highly important for environmental assessment. Therefore, a surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) system is designed to determine the RIs of single particle aerosols with diameters of less than 100 nm in the hygroscopic growth process. Measurements are taken using mixed single particles with different mass ratios. The RIs of mixed single aerosols at different RHs are retrieved by measuring the scattering light intensity using the SPRM-ARI system and almost all the RIs of the bicomponent particles with different mass ratios decrease with increasing water content under high RH conditions. Finally, for each of the bicomponent particles, the maximum standard deviations for the retrieved RI values are only 2.06×10

The refractive index points to the interplay between light and objects, which is rarely studied down to micronano scale. Herein, we demonstrated a conventional bright-field imaging technique to determine the local refractive index of single particles combined with a series of refractive index standard solutions. This intrinsic optical property is independent with the particle size and surface roughness with a single chemical component. Furthermore, we accurately tuned refractive index of homemade core-shell nanoparticles by adjusting the ratio of core-to-shell geometry. This simple and effective strategy reveals extensive applications in exploring, designing and optimizing the physical and optical characterizations of composite photonic crystals with high precision. It also indicates potentials in the field of reflective displays, optical identification, and encryption.

Most label-free techniques rely on measuring refractive index or mass change on the sensor surface. Thus, it is challenging for them to measure small molecules or enzymatic processes that only induce a minor mass change on the analyte molecules. Here, we have developed a technique by combining Surface Plasmon Resonance sensing with an Oscillating Biomolecule Layer approach (SPR-OBL) to enhance the sensitivity of traditional SPR. In addition to the inherent mass sensitivity, SPR-OBL is also sensitive to the charge and conformational change of the analyte; hence it overcomes the mass limit and is able to detect small molecules. We show that the multimetric SPR-OBL measurement allows for sensing any changes regarding mass, charge, and conformation, which expands the detection capability of SPR.

The need for self-referencing is extremely important in the field of biosensing. In this manuscript, we report on the study, design, and validation of a dual-region self-referencing fiber-optic surface plasmon resonance biosensor. One region is intended to measure and monitor the binding events of the biological sample under test, while the other one is designed to be used as a reference channel to compensate for external factors, such as bulk refractive index modifications and temperature oscillations, that can negatively affect the biomolecular interaction measurement. Two different configurations for the biosensor probe are presented and investigated here, both theoretically and experimentally. First, the theoretical performance of the proposed biosensor probes, in terms of surface plasmon resonance wavelength shift, was simulated using a numerical model. Afterward, they were experimentally validated in sucrose-water solutions and showed a response to refractive index and temperature changes with sensitivities up to 2000 nm/RIU and 1.559 nm/°C, respectively. Finally, an aptamer-based bioassay and a high-resolution melting assay were successfully implemented on the two proposed configurations, demonstrating the feasibility of analyzing the binding events and measuring other external signal modifications simultaneously using the same biosensor probe. ispartof: ACS SENSORS vol:7 issue:11 pages:3360-3368 ispartof: location:United States status: published

Time-resolved measurements of changes in the size and shape of nanobiological objects and layers are crucial to understand their properties and optimize their performance. Optical sensing is particularly attractive with h i g h throughput and sensitivity, and label-free operation. However, most state-of-the-art solutions require intricate modeling or multi-parameter measurements to disentangle conformational or thickness changes of biomolecular layers from complex interfacial refrac t i v e index variations. Here, we present a dual-band nanoplasmonic ruler comprising mixed arrays of plasmonic nanoparticles with spectrally separated resonance peaks. As electrodynamic simulations and model experiments show, the ruler enables real-time simultaneous measurements of thickness and refractive index variations in uniform and heterogeneous layers with sub-nanometer resolution. Additionally, nanostructure shape changes can be tracked, as demonstrated by quantifying the degree of lipid vesicle deformation at the critical coverage prior to rupture and supported lipid bilayer formation. In a broader context, the presented nanofabrication approach constitutes a generic route for multimodal nanoplasmonic optical sensing., ACS Nano, 16 (10), ISSN:1936-0851, ISSN:1936-086X

The refractive index (RI) is a fundamental physical property of materials. Although measurement of the RI of biological nanoparticles (BNPs) in aqueous media is of great importance to basic research and biomedical applications, it is hampered by their tiny size, large intrinsic heterogeneity, and weak scattering. Here, we report the development of a label-free technique that can determine the RI of individual viruses and small extracellular vesicles (sEVs) with high precision and an analysis rate up to 10 000 particles per minute. This was achieved via the combination of high-sensitivity light-scattering detection by nanoflow cytometry (nFCM) and the Mie theory calculation. With the measured RIs for T7 virions, T7 capsids, and sEVs, the concentrations of nucleic acid in viral particles and protein in the lumen of sEVs were estimated. Furthermore, building upon a simplified core-shell model, the RIs of sEVs ranging from 40 to 200 nm were obtained. By using these RIs, a statistically robust size distribution of sEVs was acquired in minutes with accuracy and resolution matched closely with those of cryo-TEM measurements. Our approach could become an important tool in the RI determination of single BNPs.

Metasurfaces are 2D artificial materials consisting of arrays of metamolecules, which are exquisitely designed to manipulate light in terms of amplitude, phase, and polarization state with spatial resolutions at the subwavelength scale. Traditional micro/nano-optical sensors (MNOSs) pursue high sensitivity through strongly localized optical fields based on diffractive and refractive optics, microcavities, and interferometers. Although detections of ultra-low concentrations of analytes have already been demonstrated, the label-free sensing and recognition of complex and unknown samples remain challenging, requiring multiple readouts from sensors

Medium polarity plays a crucial role in charge-transfer processes and electrochemistry. The added supporting electrolyte in electrochemical setups, essential for attaining the needed electrical conductivity, sets challenges for estimating medium polarity. Herein, we resort to Lippert–Mataga–Ooshika (LMO) formalism for estimating the Onsager polarity of electrolyte organic solutions pertinent to electrochemical analysis. An amine derivative of 1,8-naphthalimide proves to be an appropriate photoprobe for LMO analysis. An increase in electrolyte concentration enhances the polarity of the solutions. This effect becomes especially pronounced for low-polarity solvents. Adding 100 mM tetrabutylammonium hexafluorophosphate to chloroform results in solution polarity exceeding that of neat dichloromethane and 1,2-dichloroethane. Conversely, the observed polarity enhancement that emerges upon the same electrolyte addition to solvents such as acetonitrile and N,N-dimethylformamide is hardly as dramatic. Measured refractive indices provide a means for converting Onsager to Born polarity, which is essential for analyzing medium effects on electrochemical trends. This study demonstrates a robust optical means, encompassing steady-state spectroscopy and refractometry, for characterizing solution properties important for charge-transfer science and electrochemistry.

Nanophotonic waveguides that implement long optical pathlengths on chips are promising to enable chip-scale gas sensors. Nevertheless, current absorption-based waveguide sensors suffer from weak interactions with analytes, limiting their adoptions in most demanding applications such as exhaled breath analysis and trace-gas monitoring. Here, we propose an all-dielectric metamaterial-assisted comb (ADMAC) waveguide to greatly boost the sensing capability. By leveraging large longitudinal electric field discontinuity at periodic high-index-contrast interfaces in the subwavelength grating metamaterial and its unique features in refractive index engineering, the ADMAC waveguide features strong field delocalization into the air, pushing the external optical field confinement factor up to 113% with low propagation loss. Our sensor operates in the important but underdeveloped long-wave infrared spectral region, where absorption fingerprints of plentiful chemical bonds are located. Acetone absorption spectroscopy is demonstrated using our sensor around 7.33 μm, showing a detection limit of 2.5 ppm with a waveguide length of only 10 mm.

Predicting the properties of materials prior to their synthesis is of great significance in materials science. Optical materials exhibit a large number of interesting properties that make them useful in a wide range of applications, including optical glasses, optical fibers, and laser optics. In all of these applications, refraction and its chromatic dispersion can directly reflect the characteristics of the transmitted light and determine the practical utility of the material. We demonstrate the feasibility of reconstructing chromatic-dispersion relations of well-known optical materials by aggregating data over a large number of independent sources, which are contained within a material database of experimentally determined refractive indices and wavelength values. We also employ this database to develop a machine-learning platform that can predict refractive indices of compounds without needing to know the structure or other properties of a material of interest. We present a web-based application that enables users to build their customized machine-learning models; this will help the scientific community to conduct further research into the discovery of optical materials.

Silicon (Si) is promising as a field enhancement material because of its high abundance, low toxicity, and high refractive index. The field enhancement effect intensifies light-matter interactions, which improves photocatalysis, solar cell performance, and sensor sensitivity. To manufacture field enhancement materials on a production scale, the fabrication technique must be simple, cost-effective, fast, and highly reproducible and must produce a high enhancement factor (EF). Herein, we report on an economical and efficient fabrication method for a field enhancement substrate consisting of a two-dimensional Si wire array (2D-SiWA). This substrate was demonstrated as a fluorescence sensor with high sensitivity (EF200) and composed of a large area (6.0 mm

In this paper, we numerically and experimentally propose a novel hollow-core microstructured optical fiber (HC-MOF) biosensor for refractive index determination. The sensing mechanism of the proposed sensor is based on photonic bandgap effect and the location of transmission maxima of the fiber, which is strongly depend on the liquid analyte RI filled in the fiber core. The proposed HC-MOF biosensor demonstrates the spectral sensitivity of 5636.3 nm/RIU with a RI detection range of 1.333 to 1.3385 for different ratios of plasma in blood serum in our experimental studies. The HC-MOF proposed here can detect similar liquid analytes with RI close to 1.33. The proposed sensor with a high sensitivity, ease of operation and the possibility of real-time sensing has a strong potential for detection of liquid analytes and biomolecules with possible applications in medicine, chemistry, and biology.

The present work exhibits a novel design of surface plasmon resonance (SPR) biosensor, which comprises CaF2 prism, TiO2, metal (Ag/Au), PtSe2, 2D materials (graphene/ transition metal dichalcogenides (MoS2/WS2)) and sensing medium, for point-of-care detection of various stages of malaria diseases. The transfer matrix method (TMM) is employed to examine the angular reflectivity of the proposed structure after judiciously optimizing the layer thicknesses and layer numbers. Phase interrogation technique is utilised to validate the position of occurrence of resonance angles. Additionally, the proposed SPR structure is designed using COMSOL Multiphysics, to assay the electric field intensity and electric field enhancement factor near the edge of 2D material-sensing layer interface. Simulation upshots revealed that the use of new class of 2D materials catapult the sensor performance to a new height compared to the traditional SPR configuration. A maximum sensitivity of 240.10°/RIU, quality factor of 78.46 RIU-1 and detection accuracy of 1.99 is attained for Ag-based SPR configuration with bilayer of WS2. Sensing parameters are compared with previously reported works to prove the superiority of the present research. Moreover, the real-time and label-free detection of malaria diseases makes the suggested sensor worth to fabricate as a SPR chip with the recent nanofabrication technologies.

In situ refractive index sensors integrated with nanoaperture-based optical tweezers possess stable and sensitive responsivity to single nanoparticles. In most existing works, detection events are only identified using the total light intensity with directivity information ignored, leading to a low signal-to-noise ratio. Here, we propose to detect an optically trapped 20 nm silica particle by monitoring directivity of a plasmonic antenna. The main and secondary radiation lobes of the antenna reverse upon trapping because the particle-induced perturbation negates the relative phase between two antenna elements, leading to a significant change of the antenna front-to-back ratio. As a result, we obtain a signal-to-noise ratio of 20, with an order-of-magnitude improvement as compared to the intensity-only detection scheme.

The structural coloration and decoloration are problems of scientific interest for a long time. Hence, the fundamental investigations on structures and the optical properties of insect wings have been performed. As a part of such studies, we elucidate the optical properties of green lacewing wings via observation and simulation. First, we elucidate the surface pattern of green lacewing wings using a two-dimensional fast Fourier transform. A cross-shaped pattern of a Fourier spectrum is obtained, and the concise wing model with the surface protrusions arranged in a square grid on a base substrate is constructed in reference to the obtained Fourier spectrum. Next, we perform a finite-difference time-domain (FDTD) simulation to elucidate a light path through wings with and without surface protrusions. The FDTD simulation results indicate that the surface protrusions of a wing increase and decrease the intensity of the transmitted and reflected light, respectively, which is an antireflection behavior. This phenomenon was also observed in the case of 45° incident light. The intensity of transmitted light coupled to wings is induced by surface protrusions with a stepwise refractive index between air and a substrate, which induces antireflection. In particular, transmitted light is increased by the surface protrusions of wings in the range of 500-800 nm wavelength. The intensities of transmitted and reflected light are affected by the direction of incident electric field (polarization) in the case of wings with protrusions arranged in the same direction (parallel). Hence, the surface protrusions are arranged in a square grid to reduce the influence of the polarization direction.

An optical control of many working optoelectronic systems (real-time sensors, optical modulators, light amplifiers, or phase retarders) giving efficient optical gain or remote signal modulation is currently included as scientifically and industrially interesting. In here, an oxazolone derivative as the multifunctional organic system is given in this contribution. The molecule possesses a stilbene group and an oxazolone heteroatomic ring, which implies effective refractive index manipulation and multimode lasing action, respectively. The light modulation is repeatable and stable, also in the hundreds of Hz regime. On the other hand, the amplified optical signal can be easily generated by an external optical pumping source. Thus, signal control is fully available, as is read-in and read-out of the information in real time. Furthermore, this third-order, nonlinear, optical phenomenon using a third harmonic generation technique was also observed. We discovered that only by changing the energy and time regime of the supplied optical signal is the optical or nonlinear optical response observed. Two heteroenergetic molecular states (

We report on an extrinsic surface plasmon-enhancedrefractometer based on cladding mode resonance excitation in a photonic crystal fiber (PCF) equipped with a straight fiber Bragggrating (FBG). First, we show that the lattice pitch and the air hole diameter of the PCF microstructure define the spectral locationof the excited cladding mode resonances. Second, we demonstrate that if the PCF parameters are properly selected, those resonancesare sensitive to increases in steps of 1×10−4 refractive index units(RIU) of the refractive index value close to that of water. To thebest of our knowledge, this is the first time that the sensitivity of PCF cladding mode resonances to refractive index changesin water-based solutions is reported. We achieved experimental values of 40.3 nm/RIU in terms of wavelength sensitivity and −801dB/RIU in terms of amplitude sensitivity. The performance of our sensor is therefore comparable to that of tilted FBGs in step-indexfibers used for water refractometry, which indicates the potential ofour PCF sensor for biosensing. In addition, the sensor fabricationdoes not require any post-processing such as etching or polishing,which allows preserving the integrity of the fiber probe. Finally, thenarrowspectrum within which the PCF operates, allows envisagingmulti-target detection with a single fiber probe by using cascadedwavelength-multiplexed gratings.

Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light-guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10-6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

We present a microfluidic device compatible with high resolution light sheet and super-resolution microscopy. The device is a 150 μm thick chamber with a transparent fluorinated ethylene propylene (FEP) cover that has a similar refractive index (1.34) to water (1.33), making it compatible with top-down imaging used in light sheet microscopy. We provide a detailed fabrication protocol and characterize the optical performance of the device. We demonstrate that the device supports long-term imaging of cell growth and differentiation as well as the rapid addition and removal of reagents while simultaneously maintaining sterile culture conditions by physically isolating the sample from the dipping lenses used for imaging. Finally, we demonstrate that the device can be used for super-resolution imaging using lattice light sheet structured illumination microscopy (LLS-SIM) and DNA PAINT. We anticipate that FEP-based microfluidics, as shown here, will be broadly useful to researchers using light sheet microscopy due to the ability to switch reagents, image weakly adherent cells, maintain sterility, and physically isolate the specimen from the optics of the instruments.

Whispering gallery mode resonator (WGMR) microspheres yield highly structured optical spectra that are extremely sensitive to their environment and are of intense interest for use in a variety of sensing applications. Many efforts to leverage the unique sensitivities of WGMRs have relied on stringent experimental requirements to correlate specific spectral shifts/changes to an analyte/stimulus such as (1) precise positional knowledge, (2) reference spectra for each microsphere, and (3) high mechanical stability. Consequently, these factors can hinder adequate mixing or incorporation of analytes and can create challenges for remote sensing. This work describes a continuous flow technique for measuring whispering gallery mode (WGM) spectra of dye-doped microspheres suspended in solution and an accompanying analysis scheme that can extract the local refractive index without

An accurate as well as highly sensitive label-free chemical sensing platform for the detection of various metal ions was demonstrated. The chemical sensor was derived from the micro-tapered long-period fiber grating (MLPG) by depositing graphene oxide (GO) by chemical-bonding and optical-tweezer effects. The enhancement in refractive index (RI) sensitivity as well as reusability was obtained by evaluating the deposition thickness in the range of approximately 97.7 to 158.9 nm. Based on the analysis of adsorption principles, the enhanced RI sensitivity leads to a limit of detection as low as 3.2 ppb. The highest sensitivities for the cases studied using sodium and manganese ions in a wide concentration range of 1 ppb to 1 × 10

Starch occurs naturally in the form of semicrystalline granules, and is composed of two types of carbohydrate molecules, amylose (AM) and amylopectin (AP). Starch granules and starch molecules have sizes in the range of 1-100 μm and 20-250 nm, respectively; these size ranges are among the key factors affecting the functional properties of starch. Asymmetrical flow field-flow fractionation (AF4) is a size-based separation technique. The major difference between AF4 and dynamic light scattering or microscopy techniques is that AF4 enables the separation of particles based on their size; consequently, the elution profile can be converted to the size distribution of the samples. In the last two decades, AF4 systems, when coupled online with multiangle light scattering (MALS) and differential refractive index (dRI) detectors (AF4-MALS-dRI), have demonstrated to be applicable for the size characterization of starch at the molecular level. Unlike size exclusion chromatography (SEC), AF4 systems use an open channel that does not require a stationary phase or packing materials. Thus, the shear scission of AP molecules during AF4 separation is minimized. The size detection range of a commercial AF4 system ranges from 1 nm to 10 μm, which is smaller than the size range of starch granules. In this study, a home-made AF4 system was developed, and its capability for the size characterization of starch granules extracted from sweet potato, lotus seed, and rice was investigated. The performance of the developed AF4 system was evaluated by running a mixture of polystyrene (PS) with diameter of 2, 6, 12, and 20 μm, respectively. Baseline separation of four PS samples was achieved, and the resolution for 6 μm PS and 12 μm PS was 1.40. The detection limit of the developed AF4 system was higher than that of commercial AF4 systems. Thus, the developed AF4 system is promising for the separation and characterization of starch granules. The effect of the composition of the carrier liquid on the AF4 separation of starch granules was also studied. Moreover, the accuracy of AF4 in terms of size characterization of the starch granules was evaluated by optical microscopy (OM). The results revealed that the type of dispersant and viscosity of the carrier liquid affect the accuracy of size characterization of the starch granules. The size distribution of rice starch granules obtained using a carrier liquid containing 0.01% (w/v) sodium dodecyl sulfate (used as a dispersant), 0.02% (w/v) NaN3 (used as a bactericide), and 0.001% (w/v) hydroxypropylmethylcellulose (used to adjust the viscosity of the carrier liquid) was in agreement with that obtained from OM. Furthermore, a commercial AF4 system coupled with MALS and dRI detectors was employed for the separation and characterization of starch molecules. A molecularly dispersed solution is necessary for the reliable molecular characterization of starch. The effect of the starch dissolution temperature on the AF4 characterization of starch was also investigated. The optimal dissolution temperature for lotus seed and rice starch granules was 75 ℃, while that for sweet potato starch granules was 78 ℃; this difference is mainly attributed to the different botanical origins of the granules. The results showed that the ratio of the radius of gyration (Rg) to the hydrodynamic radius (Rh) of rice starch and sweet potato starch is in the range of 0.9-1.1 over the molar mass range of 10 6-108 g/mol. For rice starch, the Rg/Rh ratio is between 1.2 and 1.4. Rice starch has the highest apparent density among the three starches, indicating that rice starch molecules have a dense structure. The results demonstrated that the AF4 system developed in this study is rapid and accurate for the size characterization of starch granules. The developed AF4 system, when combined with commercial AF4 systems coupled online with MALS and dRI detectors, can provide technical support to study the relationship between the size from the nanoscale to the microscale and functional properties of starch.

Tomographic coherent imaging requires the reconstruction of a series of two-dimensional projections of the object. We show that using the solution for the image of one projection as the starting point for the reconstruction of the next projection offers a reliable and rapid approach to the image reconstruction. The method is demonstrated on simulated and experimental data. This technique also simplifies reconstructions using data with curved incident wavefronts.

International audience; This paper presents the development, the operating principle, and the experimental results of an innovative technique for the measurement of acoustic pressures in the range of 40 mHz up to 5 Hz. This new measurement technique is based on the use of a Fabry Perot refractometer in which the air density variations related to an acoustic wave can be tracked and determined by measuring the optical frequency variations of a laser locked on a longitudinal mode of the Fabry Perot cavity. This approach covers a wider range in the low and infrasonic frequencies compared to conventional sensors.

Advances in fluorescence microscopy, specifically the development of confocal and light-sheet microscopes, have enabled researchers to harness tissue clearing techniques to image-stained intact tissue samples in 3D. Using these techniques, tissue structure and biomarker distributions in 3D structures are preserved, thus allowing researchers to gain a wealth of spatial information about their tissue of interest. However, the execution of imaging these larger tissue samples can be challenging. Broadly speaking, tissue clearing techniques unify the refractive indices inside tissue samples, thus enabling deep tissue imaging on a confocal or light-sheet microscope. Here, we provide an overview to tissue clearing and 3D immunohistochemistry staining in general and discuss some difficulties that researchers may encounter when using these techniques. We then focus on imaging CLARITY-processed samples with both confocal and light-sheet microscopes and optimizing the acquisition parameters, before noting potential issues that may come up in imaging.

Background Colostral concentration of immunoglobulins (Ig) is crucial for the passive transfer of antibodies from the cow to the new-born calf. Direct determination of Ig by the gold standard radial immunodiffusion method is demanding in terms of time and costs. For this reason, a refractometer is commonly used at the farm level for an indirect estimation of colostrum quality, which is given as the Ig concentration. In this study, colostrum samples were collected from 548 Italian Holstein cows within 6 h of calving. The refractive index (BRIX, %) of these samples was assessed using a portable optical refractometer, as well as the concentration of total protein, IgG, IgA, and IgM by radial immunodiffusion. A four-trait animal model was used to estimate genetic parameters for BRIX and the different immunoglobulin isotypes. A receiver operating characteristic analysis was carried out to evaluate the BRIX diagnostic accuracy. Results Colostral BRIX was moderately heritable (0.26) and its genetic and phenotypic correlations with IgG (0.91, 0.78), IgA (0.57, 0.57), and IgM (0.71, 0.61) were all positive and of similar order, although the genetic correlations were generally higher than the phenotypic correlations. Low-quality colostrum samples, defined as those with an IgG concentration lower than 50 g/L, were accurately identified by the refractive index on the BRIX scale, with an area under the curve of 0.90. Conclusions The use of a refractometer is recommended on dairy farms to produce a proxy for colostral Ig concentration. BRIX is a useful phenotyping tool that can be used in cattle to improve the quality of colostrum for first feeding of calves through both traditional genetic and genomic strategies. Improving colostrum quality will reduce the incidence of failure of passive transfer of immunity in young stock.

Transparency of biological specimens is crucial to obtaining detailed 3-dimensional images and understanding the structure and function of biological specimens. This transparency or tissue clearing can be achieved by adjusting the refractive index (RI) with embedding media and removing light barriers such as lipids, inorganic deposits, and pigments. Many currently available protocols consist of multiple steps to achieve sufficient transparency, making the process complex and time-consuming. Thus, in this study, we tailored the recipe for RI adjustment media named MAX based on the recently reported MACS protocol to achieve a single-step procedure, especially for ECM-rich tissues. This was achieved by the improvement of the tissue penetrability of the RI-matching reagent by combining MXDA with sucrose or iodixanol. While this was sufficient for the 3D imaging in many applications, MAX can also be combined with modular processes for de-lipidation, de-coloration, and de-calcification to further maximize the transparency depending on the special features of the tissues. Our approach provides an easy alternative for tissue clearing and 3D imaging.

Fringe pattern based measurement techniques are the state-of-the-art in full-field optical metrology. They are crucial both in macroscale, e.g., fringe projection profilometry, and microscale, e.g., label-free quantitative phase microscopy. Accurate estimation of the local fringe orientation map can significantly facilitate the measurement process in various ways, e.g., fringe filtering (denoising), fringe pattern boundary padding, fringe skeletoning (contouring/following/tracking), local fringe spatial frequency (fringe period) estimation, and fringe pattern phase demodulation. Considering all of that, the accurate, robust, and preferably automatic estimation of local fringe orientation map is of high importance. In this paper we propose a novel numerical solution for local fringe orientation map estimation based on convolutional neural network and deep learning called DeepOrientation. Numerical simulations and experimental results corroborate the effectiveness of the proposed DeepOrientation comparing it with a representative of the classical approach to orientation estimation called combined plane fitting/gradient method. The example proving the effectiveness of DeepOrientation in fringe pattern analysis, which we present in this paper, is the application of DeepOrientation for guiding the phase demodulation process in Hilbert spiral transform. In particular, living HeLa cells quantitative phase imaging outcomes verify the method as an important asset in label-free microscopy.

The laminar flow interface (LFI) developed at low Reynolds numbers is one of the most prominent features of microscale flows and has been employed in a diverse range of optofluidic applications. The formation of LFIs usually requires the manipulation of multiple streams within a microchannel using a complex hydrodynamic pumping system. Herein, we present a new type of LFI that is generated by fluid switching within a three-dimensional (3D) microlens-incorporating microfluidic chip (3D-MIMC). Since Poiseuille flows exhibit a parabolic velocity profile, the LFI is cone-like in shape and acts as a transient refractive interface (TRI), which is sensitive to the refractive index (

Imaging platforms that enable long-term, high-resolution imaging of biofilms are required to study cellular level dynamics within bacterial biofilms. By combining high spatial and temporal resolution and low phototoxicity, lattice light sheet microscopy (LLSM) has made critical contributions to the study of cellular dynamics. However, the power of LLSM has not yet been leveraged for biofilm research because the open-on-top imaging geometry using water-immersion objective lenses is not compatible with living bacterial specimens; bacterial growth on the microscope's objective lenses makes long-term time-lapse imaging impossible and raises considerable safety concerns for microscope users. To make LLSM compatible with pathogenic bacterial specimens, we developed hermetically sealed, but optically accessible, microfluidic flow channels that can sustain bacterial biofilm growth for multiple days under precisely controllable physical and chemical conditions. To generate a liquid- and gas-tight seal, we glued a thin polymer film across a 3D-printed channel, where the top wall had been omitted. We achieved negligible optical aberrations by using polymer films that precisely match the refractive index of water. Bacteria do not adhere to the polymer film itself, so that the polymer window provides unobstructed optical access to the channel interior. Inside the flow channels, biofilms can be grown on arbitrary, even nontransparent, surfaces. By integrating this flow channel with LLSM, we were able to record the growth of S. oneidensis MR-1 biofilms over several days at cellular resolution without any observable phototoxicity or photodamage.

The behavior of self-assembly of C60 molecules in solutions of C60/hexane/xylene were studied by the methods of refractometry, ultraviolet–visible spectroscopy and dynamic light scattering (DLS). I...

International audience; Evanescent-wave scattering is a topic in classical electrodynamics and in the study of colloidal particles near a boundary. However, how such near-surface scattering at subcellular refractive-index heterogeneities degrades the excitation confinement in biological total internal reflection fluorescence microscopy has not been well studied. An elegant theoretical work by Axelrod and Axelrod now addresses this very relevant question and reveals that-even when scattered-evanescent light preserves some of its surprising optical properties.

Oscillation of micron-sized liquid droplet is an interesting and common phenomenon, and is used to measure surface tension and viscosity with the recently developed time-resolved rainbow refractometry. Droplets produced by a monodisperse droplet generator are excited to oscillate at a small amplitude (less than 1%) and high frequency (of the order of 10 kHz) by applying a periodic tiny disturbance. The aspect ratio of a spheroidal droplet is quantified by time-resolved angular shift of rainbow signal. Thus the droplet shape oscillation is quantified by its unsphericity, instead of calculated from the polar radius or the variation of surface area. Experiments on several liquids were conducted to evaluate the validation of the experimental system. The results present that the relative errors of measured values of the surface tension and viscosity are less than 5% and 10%, respectively, promising the great potential of rainbow refractometry for liquid surface properties measurement.

A technique is implemented for altering the multimodal resonance generated in an ultrathin silicon ring resonator-based terahertz (THz) absorber. The absorber provides the dual-band resonance with the excitation of magnetic and electric dipole in the lower and upper band, respectively. The field of magnetic and electric dipoles is altered using a non-resonant graphene ring placed in the center of the generated dipolar arrangement and the tunability and perfect absorption is achieved. A circuit model is prepared using transmission line method and absorber operation is verified. The proposed absorber can be utilized as a biosensor for the detection of malaria virus and glucose percentage in water. The sensor offers highest sensitivity as 0.29 and 0.27 THz per thickness unit change and quality factor as 117.53 and 245 in the lower and upper band, respectively during the sensing of analyte thickness. Also, it offers the sensitivity as 0.20 and 0.10 THz per refractive index unit change and quality factor as 105.28 and 211.84 in the lower and upper band, respectively during refractive index sensing. Moreover, the structure remains insensitive to polarization angle of the incident electromagnetic wave.

Both the nonclose-packed structure and the large refractive index contrast of guanine nanocrystals and cytosols in iridophores play a vital role in the dynamic camouflage of chameleons, including the bright skin color and color tuning sensitivity to external stimulus. Here, the nonclose-packed photonic crystals consisting of ZnS nanospheres and polymers, which have similar refractive indices with guanine nanocrystals and cytosols, respectively, are constructed by a two-step filling strategy. ZnS@SiO2 nanospheres are self-assembled to build intermediate close-packed photonic crystals followed by filling polymers in their interstices. The nonclose-packed photonic crystal is successfully achieved when the silica portion is etched by HF solution and refilled by polymers. Excitingly, the stimulus response of the designed photonic crystal is as sensitive as the skin of chameleons due to the similar contrast of refractive indices and nonclose-packed structure. The reflection peak of the structure can blue-shift more than 200 nm as the temperature increases from 30 to 55 °C or under 20% compressional strain. This work not only builds the nonclose-packed photonic crystals by introducing a two-step filling strategy but also proves that high refractive contrast in photonic crystals is an effective strategy to achieve ultrasensitivity, which is highly desirable for various applications.

Supplying newborn calves with immunoglobins is critical for their health and a daily challenge in the dairy industry. Among various factors determining colostrum quality, the prepartum metabolic status of the cow might be of particular importance. The objective of this observational cross-sectional study was to evaluate relationships between cow-level variables and the colostrum quality as determined by Brix refractometry. A total of 873 cows of varying breed and parity from 124 German dairy herds were included in the study, and blood and urine samples were taken 3 to 1 wk before the expected calving date. Effectively, samples were collected on average 8.2 d (geometric mean) before calving, ranging from 2 to 45 d. The final variable set included body condition score, lameness score, breed, parity, vaccination of the cow, the activity of glutamate dehydrogenase and aspartate aminotransferase, the urine concentration of creatinine, net acid-base excretion, the serum concentration of cholesterol and calcium, and the difference in albumin and total protein concentration. Generalized linear mixed effects regression models with hierarchically structured random effects (cow within herd) using the maximum likelihood method were fitted to the data to identify associations between the Brix value as an outcome and cow-level variables as predictors. Cows entering second parity had lower Brix values compared with cows entering third or greater parity, and prepartum vaccination of cows led to higher Brix values compared with nonvaccinated cows. Cows with a moderate to high lameness score had lower Brix values than cows with low-grade lameness. An increase of glutamate dehydrogenase serum activity and serum calcium concentration were associated with lower Brix values, whereas an increase in the difference of total protein and albumin serum concentration led to higher Brix values. In conclusion, the metabolic health of the cow affects colostrum quality and may cause failure of passive immunoglobulin transfer as well as impaired calf health.

Herein, a novel liquid crystal microarray (LCM) film with optical regulation ability is first constructed by combining liquid crystals (LC) and the highly ordered microporous structure of inverse opal photonic crystals (IOPhCs). The LCM films are fabricated by infiltrating LC molecules into the LC polymer with the structure of IOPhCs, and their properties are very different from those without the LC. Interestingly, the optical property of LCM films can be controlled by changing the orientation of LC molecules, which varies with the interfacial force. In combination with polarization images, spectral reflection peak, circular dichroism spectra, potential difference, and fluorescence images of LCM films, the mechanism of this change is investigated. It is found that the exposed basic group of single-stranded DNA is the key to the change of the optical property of LC microarrays. Meanwhile, the optical signals of LC microarrays based on the PhCs provide a novel LC signal mode for an LC sensing system (microspectral signal mode), and it can be recorded by a fiber-optic spectrometer, which is a great improvement on LC sensing signals. Therefore, the LC microarray sensing signal can be used for accurate analysis of targets by the change of the reflection peak intensity of PhCs. When the LC molecules are induced by different aptamers, the LC microarray sensing interface can be further used for the determination of different targets, such as cocaine and Hg2+. The research on LCM films is of significant value for the development of LC sensing technology and also shows great application prospects in biochemical sensing fields.

Terahertz (THz) spectroscopy is a powerful tool for unambiguously extracting complex-valued material properties (e.g., refractive index, conductivity, etc.) from a wide range of samples, with applications ranging from materials science to biology. However, extracting complex refractive indices from THz time-domain spectroscopy data can prove challenging, especially for multilayer samples. These challenges arise from the large number of transmission-reflection paths the THz pulse can take through the sample layers, leading to unwieldy strings of Fresnel coefficients. This issue has often been addressed using various approximations. However, these approximations are only applicable to specific classes of samples and can give erroneous results when misapplied. An alternative to this approach is to programmatically model all possible paths through the sample. The many paths through the sample layers can be modeled as a tree that branches at every point where the paths diverge, i.e., whenever the pulse can either be transmitted or reflected. This tree can then be used to generate expressions relating the unknown refractive index to the observed time domain data. Here, we provide a freely available open-source package implementing this method as both a MATLAB library and a corresponding graphical user interface, which can also be run without a MATLAB license (https://github.com/YaleTHz/nelly). We have tested this method for a range of samples and compared the results to commonly used approximations to demonstrate its accuracy and wide applicability. Our method consistently gives better agreement than common approximations.

Critical angle refractometry is an established technique for determining the refractive index of liquids and solids. For transparent samples, the critical angle refractometry precision is limited by incidence angle resolution. For lossy samples, the precision is also affected by reflectance measurement error. In the present study, it is demonstarted that reflectance error can be practically eliminated, provided that the sample’s extinction coefficient is a priori known with sufficient accuracy (typically, better than 5%) through an independent measurement. Then, critical angle refractometry can be as precise with lossy media as with transparent ones.

Exosomes are abundantly secreted by most cells that carry membrane and cytosolic factors that can reflect the physiologic state of their source cells and thus have strong potential to serve as biomarkers for early diagnosis, disease staging, and treatment monitoring. However, traditional diagnostic or prognostic applications that might use exosomes are hindered by the lack of rapid and sensitive assays that can exploit their biological information. An array of assay approaches have been developed to address this deficit, including those that integrate immunoassays with nanoplasmonic sensors to measure changes in optical refractive indexes in response to the binding of low concentrations of their targeted molecules. These sensors take advantage of enhanced and tunable interactions between the electron clouds of nanoplasmonic particles and structures and incident electromagnetic radiation to enable isolation-free and ultrasensitive quantification of disease-associated exosome biomarkers present in complex biological samples. These unique advantages make nanoplasmonic sensing one of the most competitive approaches available for clinical applications and point-of-care tests that evaluate exosome-based biomarkers. This review will briefly summarize the origin and clinical utility of exosomes and the limitations of current isolation and analysis approaches before reviewing the specific advantages and limitations of nanoplasmonic sensing devices and indicating what additional developments are necessary to allow the translation of these approaches into clinical applications.

This paper first reports a liquid-core hydrogel optical fiber fluorescence probe. It is composed of a liquid core, a high-refractive-index hydrogel fiber core, and a low-refractive-index hydrogel fiber cladding, which is completely different from many existing optical fiber fluorescence probes. The sensing solution with sensitive materials is sealed as a liquid core, and it can sufficiently react with small-molecule targets penetrating through the hydrogel fiber cladding and core, thus inducing variations in the fluorescence signals. These fluorescence signals can be localized and transmitted within the probe and finally collected and quantified for target detection. This proposed probe can be simply and rapidly fabricated and reused, and it was proven to have high sensitivity, accuracy, and selectivity in practical applications. Therefore, this liquid-core hydrogel optical fiber fluorescence probe will enable a novel sensing platform for small-molecule analyte detection that faces on-site detection challenges.

In this research, we propose a novel nonlinear delta-function photonic crystal for detecting sodium iodide (NaI) solution of different concentrations. The suggested structure comprises 50 delta stacks of GaP in an aqueous solution of NaI. These stacks are considered to have weak defocusing nonlinearity in the order of 10−6 (V/m)−2. Due to nonlinearity of the design, a defect-like resonance is formed within the photonic band gap. Thus, the detection of NaI with different concentrations can be easily investigated without the inclusion of a defect through the photonic crystal structure. The effects of both the linear part of the refractive index of GaP layers and nonlinear coefficient on the transmittance value are thoroughly discussed. The numerical findings investigate that the resonant peak begins to split at some critical nonlinearity. In our proposed structure, splitting occurs at about − 12 × 10−6 (V/m)−2. In this regard, the suggested sensor provides a high sensitivity of 409.7 nm/RIU and a wonderful detection limit of 0.0008.

Microlens arrays (MLAs) are acquiring a key role in the micro-optical system, which have been widely applied in the fields of imaging processing, light extraction, biochemical sensing, and display technology. Compared with solid MLAs, liquid MLAs have received extensive attention due to their natural smooth interface and adjustability. However, manufacturing tunable liquid MLAs with ideal structures is still a key challenge for current technologies. In this paper, a novel and simple optofluidic method is demonstrated, enabling the tunable focusing and high-quality imaging of liquid MLAs. Tunable droplets are fabricated and self-assembled into arrays as the MLAs, which can be easily adjusted to focus, form images, and display different focal lengths. Tuning of MLAs' focusing properties (range from 550 to 5370 μm) is demonstrated by changing the refractive index (RI) of the droplets with a fixed size of 200 μm, which can be changed by adjusting the flow rates of the two branch streams. Also, the corresponding numerical apertures of the MLAs range from 0.026 to 0.26. Furthermore, the MLAs' functionality for microparticle imaging applications is also illustrated. Combining the MLAs with a 4× objective, microparticle imaging is magnified two times, and the resolution has also been improved on the original basis. Besides, both the size and RI of the MLAs in an optofluidic chip can be further adjusted to detect samples at different positions. These MLAs have the merits of high optical performance, a simple fabrication procedure, easy integration, and good tunability. Thus, it shows promising opportunities for many applications, such as adaptive imaging and sensing.

The design of a refractometric sensing system for liquids analysis with a sensor and the scheme for its intensity interrogation combined on a single photonic integrated circuit (PIC) is proposed. A racetrack microring resonator with a channel for the analyzed liquid formed on the top is used as a sensor, and another microring resonator with a lower Q-factor is utilized to detect the change in the resonant wavelength of the sensor. As a measurement result, the optical power at its drop port is detected in comparison with the sum of the powers at the through and drop ports. Simulations showed the possibility of registering a change in the analyte refractive index with a sensitivity of 110 nm per refractive index unit. The proposed scheme was analyzed with a broadband source, as well as a source based on an optoelectronic oscillator using an optical phase modulator. The second case showed the fundamental possibility of implementing an intensity interrogator on a PIC using an external typical single-mode laser as a source. Meanwhile, additional simulations demonstrated an increased system sensitivity compared to the conventional interrogation scheme with a broadband or tunable light source. The proposed approach provides the opportunity to increase the integration level of a sensing device, significantly reducing its cost, power consumption, and dimensions.

This work describes a 3D-printed optofluidic fiber sensor to measure refractive index in real time, combining a microfluidic system with an optical fiber extrinsic Fabry–Perot interferometer. The microfluidic chip platform was developed for this purpose through 3D printing. The Fabry–Perot cavity was incorporated in the microfluidic chip perpendicularly to the sample flow, which was of approximately 3.7 µL/s. The optofluidic fiber sensor platform coupled with a low-cost optical power meter detector was characterized using different concentrations of glucose solutions. In the linear regression analysis, the optical power shift was correlated with the refractive index and a sensitivity of −86.6 dB/RIU (r2 = 0.996) was obtained. Good results were obtained in terms of stability with a maximum standard deviation of 0.03 dB and a sensor resolution of 5.2 × 10−4 RIU. The feasibility of the optofluidic fiber sensor for dynamic analyses of refractive index with low sample usage was confirmed through real-time measurements.

We put forward a dual-mode photonic crystal nanobeam cavity for simultaneous sensing of the refractive index (RI) and temperature (T) designed with the assistance of artificial neural networks (ANNs). We choose the structure of quadratically tapered elliptical holes with a slot to improve the sensitivities of the two modes. To reduce the time consumption of the design, the ANNs are trained to predict the band structure and to inverse design the geometric structure. For the forward prediction and the inverse design neural networks, low mean square errors of 5.1 × 1 0 − 4 and 1.4 × 1 0 − 2 are achieved, respectively. Through a specific design of band properties by the well-trained neural networks, a dual-mode nanobeam sensor with high quality factors of 9.34 × 1 0 4 and 1.55 × 1 0 5 and a small footprint of 23.8 × 0.7 µ m 2 are designed. The RI and T sensitivities of the air mode are 405 nm/RIU and 40 pm/K, respectively, whereas those of the dielectric mode are 531 nm/RIU and 27 pm/K, respectively. The present work shows significance in further research on the design and applications for dual-mode cavities.

A fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index measurement, but there is less research on curvature measurement. In this paper, a single-mode fiber curvature sensor based on SPR is designed and fabricated. By employing bending, the transmitted light in the fiber core leaks into the cladding. A 50 nm gold film is coated outside the cladding, and the evanescent field of the cladding after bending contacts the gold film to cause SPR. When the curvature changes, the coupled cladding mode and intensity are different; that is, the SPR incident angle and evanescent field intensity are different, so as to realize the dual parameters of SPR resonance wavelength and depth of the resonance valley changing with curvature. By experiments, the influence of different cutoff wavelengths of single-mode fiber on the performance of the sensor is studied. The testing results indicate that with the decrease in cutoff wavelength of the single-mode fiber, the valley depth sensitivity of the sensor increases, and the half height width (FWHM) decreases. When the cutoff wavelength of the single-mode fiber is 630 nm, the valley depth sensitivity of the sensor is 0.0088 a . u / m − 1 , the wavelength sensitivity is 0.26 n m / m − 1 , and the average FWHM is only 21 nm. The proposed single-mode fiber curvature sensor based on SPR has a narrow FWHM and an opening threshold. It can also realize no opening threshold by introducing a coreless fiber, which provides a new solution, to the best of our knowledge, for the diversified detection of fiber SPR sensors.

Salinity is an important environmental factor regulating the aquatic system structure of lakes and other water bodies. Changes in salinity, which can be caused by human activities, can adversely impact the life of water organisms. The refractive index, which can be directly related to water salinity, also controls the polarimetric properties of light reflected from the water surface. In this study, polarimetric measurements of smooth water surfaces with different salinity content were performed at different viewing zenith angles in the wavelength range of 450–1000 nm in the specular reflection directions. The results show that the light reflected from the water surface (defined as reflectance factor) in one measurement direction can be replaced by the reflectance factor derived from polarimetric measurements, and if the polarizer absorptance is considered, the average relative difference is less than 3%. The degree of linear polarization (DOLP) was used to retrieve the refractive indices of water with different salinities based on the Fresnel reflection coefficient. The inverted refractive indices not only have high accuracy (uncertainty from 0.9% to 1.8%) but also have a very strong relationship with the water salinity content. Our study shows the possibility of estimating the variation in water salinity using multi-angular polarimetric measurements.

This theoretical investigation proposes the preliminary stage detection of cancer cells using a prism-based surface plasmon resonance biosensor. The surface plasmon resonance (SPR) biosensor is label-free and rapid; it supports real-time investigations, including greater sensitivity, and it has an enormous possibility for detecting different forms of cancer. The refractive index alteration of cancer cells is 1.360-1.401. The performance of the SPR sensor has been analyzed. The different types of cancer cells for skin, cervical, blood, adrenal, and breast (type I and II) have been analyzed, and sensitivities of 292, 384, 229, 242, 254, and 261 (degree/RIU) have been achieved, respectively. A high figure of merit of 115.2

The fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index detection, and there are few reports on SPR sensors used for strain measurement. In this paper, we propose and demonstrate an S-type fiber strain sensor based on SPR. The simulation and testing results indicate that the smaller the vertical axis offset of S-type fiber is, the larger the incidence angle of SPR is, and the closer the working band of SPR is to the shorter wavelength direction. By electrofusion, we fabricated an S-type structure on the single-mode fiber, and by the S-type structure, the high-order cladding mode was excited. A 50 nm gold film was coated on the surface of the fiber cladding behind the S-type structure. The evanescent field of the cladding mode contacted the gold film to produce SPR, and the strain can change the vertical axis offset of the S-type fiber and further change the incidence angle of SPR; hence an S-type fiber strain sensor based on SPR was realized. When the refractive index of the ambient medium is 1.345 RIU, the vertical axis offset and length of the S-shaped structure are 87 and 501 µm, respectively, the resonance wavelength of the fiber SPR strain sensor changes from 648.06 to 631.77 nm with a strain detection range of 0 − 1200 µ ε , and its sensitivity is − 14.38 p m / µ ε . The proposed sensor provides a new solution for the strain measurement of the fiber SPR sensor, which is expected to be used in the fields of engineering, health monitoring, and early warning.