Direct Optical Measurement Research Articles

Direct optical measurement of intramolecular distances with angstrom precision.

Optical investigations of nanometer distances between proteins, their subunits, or other biomolecules have been the exclusive prerogative of Förster resonance energy transfer (FRET) microscopy for decades. In this work, we show that MINFLUX fluorescence nanoscopy measures intramolecular distances down to 1 nanometer-and in planar projections down to 1 angstrom-directly, linearly, and with angstrom precision. Our method was validated by quantifying well-characterized 1- to 10-nanometer distances in polypeptides and proteins. Moreover, we visualized the orientations of immunoglobulin subunits, applied the method in human cells, and revealed specific configurations of a histidine kinase PAS domain dimer. Our results open the door for examining proximities and interactions by direct position measurements at the intramacromolecular scale.

Enzyme-Free In-Situ Electrochemical Measurement Using a Porous Membrane Electrode for Glucose Transport into Cell Spheroids.

Microphysiological systems have attracted attention because of their use in drug screening. However, it is challenging to measure cell functions in real time using a device. In this study, we developed a cell culture device using a porous membrane electrode for in situ electrochemical glucose measurements for cell analysis. First, a porous membrane electrode was fabricated and electrochemically evaluated for enzyme-free glucose measurement. Subsequently, the glucose uptake of MCF-7 spheroids was evaluated using living spheroids, fixed spheroids, supernatants, and glucose transporter inhibitor-treated spheroids. Conventionally, the direct optical measurement of glucose uptake requires fluorescence-labeled glucose derivatives. In addition, the glucose uptake can be evaluated by measuring the glucose concentration in the medium by optical or electrochemical measurements. However, glucose needs to be consumed in the entire cell culture medium, which needs a long culture time. In contrast, our system can measure glucose in approximately 5 min without any labels because of in situ electrochemical measurements. This system can be used for in situ measurements in in vitro cell culture systems, including organ-on-a-chip for drug screening.

Tunable quantized spin Hall effect of light in graphene

The spin Hall effect of light is an appealing toolset for metrology that holds incredible potential for precision measurements due to its high sensitivity to the refractive index and nanostructure physical parameters. Here, we theoretically examine the quantized spin Hall effect of light on the surface of a monolayer graphene–substrate system subjected to an external perpendicular magnetic field. We discuss the impact of Landau levels induced by the external magnetic field B and the photon energy on magneto-optical conductivities and Fresnel reflection coefficients. We find that the spin-dependent splittings in graphene exhibit quantized characteristics due to the Landau levels quantization of the magneto-optical conductivities and Fresnel’s reflection coefficients near the Brewster angle. Moreover, the spin-dependent shifts are quantized and show oscillatory behavior with changes in the magnetic field and the photon energy. Our results manifest that the quantized photonic spin-dependent separations are sensitive to variations in the incidence angle, magnetic field, and incident photonic energies. The quantized spin-dependent splitting opens a promising route to find the quantized Hall conductivity and discrete Landau levels in the monolayer graphene by a direct optical weak measurement.

Optimal Sensor Placement for Mold Level in Continuous Casting

For high product quality in the continuous casting of steel, it is important that the liquid steel level in the mold remains constant and that its surface is fat. A slag layer on top of the liquid steel surface prevents direct optical measurement of the surface. However, knowing the mold level and surface shape is essential for quality monitoring and feedback control. The current paper addresses the optimal placement of mold-level sensors, given that their number is limited. The actual estimation of the surface shape is performed by an observer that receives mold-level measurements as input. The computed optimal sensor positions are validated based on experimental data from a full-scale laboratory water model of the continuous caster.

The acoustic size of the Sun

ABSTRACT Analysis of f-mode frequencies has provided a measure of the radius of the Sun which is lower, by a few hundredths per cent, than the photospheric radius determined by direct optical measurement. Part of this difference can be understood by recognizing that it is primarily the variation of density well beneath the photosphere of the star that determines the structure of these essentially adiabatic oscillation modes, not some aspect of radiative intensity. In this paper we attempt to shed further light on the matter, by considering a differently defined, and dynamically more robust, seismic radius, namely one determined from p-mode frequencies. This radius is calibrated by the distance from the centre of the Sun to the position in the subphotospheric layers where the first derivative of the density scale height changes essentially discontinuously. We find that radius is more-or-less consistent with what is suggested by the f modes. In addition, the interpretation of the radius inferred from p modes leads us to understand more deeply the role of the total mass constraint in the structure inversions. This enables us to reinterpret the sound-speed inversion, suggesting that the positions of the photosphere and the adiabatically stratified layers in the convective envelope differ non-homologously from those of the standard solar model.

Vapor distribution changes evaporative flux profiles of a sessile droplet

HypothesisWe propose that during the evaporation of sessile droplets, the evaporative flux profile is primarily influenced by droplet geometry and composition under diffusion-limited conditions. Most studies have focused solely on the evaporation feature from the liquid to the gas phase, neglecting the extent to which the evaporated vapors affect the evaporation process. We hypothesize that if the molecular weight of the evaporated vapors is significantly high or low compared to the ambient gas, it could alter the evaporative flux. ExperimentsWe employed a direct optical measurement technique, specifically Mach-Zehnder interferometry. This demonstrated that the distribution of evaporated vapor molecules can substantially modify the evaporative flux profile. FindingsOur study discovered that substantial density gradients between vapor and air could either suppress or enhance the evaporative flux, depending on the droplet's orientation. This research offers fresh insights into evaporative fluxes by taking into account the relative vapor concentration and gravitational effects.

One-Step Rapid and Sensitive ASFV p30 Antibody Detection via Nanoplasmonic Biosensors.

African swine fever (ASF) is one of the most serious transnational swine diseases in the world. The case fatality rate of susceptible pigs is up to 100%. Currently, no commercial vaccine is available, so the prevention and control of ASF mainly relies on early diagnosis and culling of infected pigs. As the ASF virus continues to evolve, develop, and diversify, nucleic acid testing becomes less efficient. Here, we developed a method for the rapid and direct optical measurement of African swine fever virus (ASFV) antibody in vitro. This one-step procedure requires nearly no sample preparation and involves p30 protein-specific label-free integration into standard 96-well plates. Using a nanoplasmonic biosensor with extraordinary optical transmission (EOT) effect, one-step sample addition, ASFV antibody was detected within 20 min. The positive antibody showed a satisfactory sensitivity and linear relationship in the dilution ratio of 1:100-1:16000. It was used for the detection of clinical serum samples with a coincidence rate of 96.6%. The measurement results can be automatically analyzed and displayed on a conventional microplate meter computer and connected device. Our detection method can be widely applied in point-of-care testing (POCT) of ASFV antibody in pig farms. IMPORTANCE African swine fever (ASF) is a serious transnational disease caused by the African swine fever virus (ASFV), which is highly contagious in wild boars and domestic pigs. There is currently no available vaccine for ASF; therefore, development efforts are a key priority as ASFV continues to evolve and diversify. The ASF antibody rapid detection platform comprising the nanoplasmonic biosensor with extraordinary optical transmission effect can greatly reduce the detection time and improve detection flux while maintaining detection sensitivity and specificity. The one-step sample addition can effectively avoid cross contamination of samples in the detection process. The detection method provides a solution for the rapid and accurate real-time monitoring of ASF in pig farms.

Quantitative Characterization of the Anisotropy of the Stress-Optical Properties of Polyethylene Terephthalate Films Based on the Photoelastic Method.

Polyethylene terephthalate (PET) is one of the most commonly used substrate materials in the field of flexible electronics, and its stress-induced birefringence often has a detrimental effect on the optical properties of the device. Therefore, a deep and systematic understanding of the stress-optical properties of PET films is crucial for device design and manufacture. The photoelastic method is a direct optical measurement technique based on the stress-induced birefringence effect of materials, which has the advantages of being nondestructive and noncontact. In this work, the photoelastic method was used to quantitatively characterize the anisotropy of the stress-optical properties of PET films under the uniaxial stress state. First, a self-built reflection-transmission coaxial bidirectional photoelasticity measurement system was developed by means of a combination of transmission and reflection photoelasticity. Then, the stress-optical coefficients and isoclinic angles of PET films with different stretching angles were measured. Finally, the linear combinations of the photoelastic tensor components and refractive-index-related parameters were determined by fitting the analytical relationship between the stress-optical coefficients and isoclinic angles.

A Method for Measuring Contact Points in Human-Object Interaction Utilizing Infrared Cameras.

This article presents a novel method for measuring contact points in human–object interaction. Research in multiple prehension-related fields, e.g., action planning, affordance, motor function, ergonomics, and robotic grasping, benefits from accurate and precise measurements of contact points between a subject’s hands and objects. During interaction, the subject’s hands occlude the contact points, which poses a major challenge for direct optical measurement methods. Our method solves the occlusion problem by exploiting thermal energy transfer from the subject’s hand to the object surface during interaction. After the interaction, we measure the heat emitted by the object surface with four high-resolution infrared cameras surrounding the object. A computer-vision algorithm detects the areas in the infrared images where the subject’s fingers have touched the object. A structured light 3D scanner produces a point cloud of the scene, which enables the localization of the object in relation to the infrared cameras. We then use the localization result to project the detected contact points from the infrared camera images to the surface of the 3D model of the object. Data collection with this method is fast, unobtrusive, contactless, markerless, and automated. The method enables accurate measurement of contact points in non-trivially complex objects. Furthermore, the method is extendable to measuring surface contact areas, or patches, instead of contact points. In this article, we present the method and sample grasp measurement results with publicly available objects.

Topological Imbert–Fedorov shifts in silicene

In this paper, we study the topological Imbert–Fedorov (IF) shifts of a light beam reflected from a silicene–substrate system in the presence of an externally applied electric field and circularly polarized beam. Silicene is a topological material and due to the strong spin–orbit interaction has a rich phase diagram. Using the famous Kubo formalism, we derive analytical expressions for the longitudinal and transverse Hall conductivities of silicene. By employing angular spectrum analysis, the analytical expression of the spatial IF shift is obtained. We show that electric field/circularly polarized light beam modulated positive and negative spatial beam shifts can be obtained by tuning the angle of incidence near the Brewster angle and the incident photonic energy in the terahertz regime. Furthermore, we also investigate the IF shifts in different topological phases of the silicene by driving the system through distinct topological quantum phase transitions (TQPTs), i.e., from topologically nontrivial to a semi-metallic state and further to a band insulating state by manipulating the interplay between the electric field and circularly polarized light beam. We believe these results are helpful for developing novel optoelectronic, spintronic, and valleytronic devices and may provide a possible technique for probing Berry curvature, topological Chern numbers, and TQPTs by direct optical measurement.

POFBG-Based Humidity Detection Method for Insulating Gas in Electrical Equipment

The accumulation of moisture content undoubtedly threatens the safe operation of gas-insulated electrical equipment. On-line humidity monitoring of SF6 is an important way to check the insulation status of live equipment. This paper presents a direct optical measurement method based on a Polymethyl Methacrylate Fiber Bragg Grating (POFBG) sensor for the humidity detection requirement of SF6 gas with a very small water content. The experiments results show that this method is feasible with the sensitivity and resolution of the POFBG sensor studied being 14.3pm/%RH and 0.1%RH in the range of 8.4~30.4%RH. Additionally, the temperature variation can affect the relative humidity change of GIS and other sealed containers. Therefore, a reduction method of relative humidity centered on the initial baseline conditions under the condition of constant water content is also proposed. It can eliminate the error in relative humidity measurement caused by temperature variation.

Development of real-time measurement system for emission and absorption of visible light during heavy gamma-ray irradiation

A system for the real-time measurement of the visible light emission from and absorption by a material in an intense gamma-ray field was developed. A white light-emitting diode produces a visible light beam that passes through an irradiated specimen and is measured by an ultraviolet–visible spectrophotometer through a long glass optical fiber accompanied with a Pb shielding configuration. A video camera provides real-time visual observation of the gradual change in the color state of the irradiated specimens. In order to study the formation of silver nanoparticles in detail, blue color dye was added to the radiolytic medium and its color change was examined as a function of irradiation dose to observe the interaction among radiation-introduced radicals in water, generated silver nanoparticles, and dye molecules. A mutual impact between the formation of silver nanoparticles and the deformation of the dye during gamma radiolysis are experimentally clarified. The combination of direct visual observation and optical absorption measurement is expected to provide powerful clues for elucidating various phenomena caused by irradiation effects.

Weak-value amplification for the optical signature of topological phase transitions

We show that weak measurements can be used to measure the tiny signature of topological phase transitions. The signature is an in-plane photonic spin Hall effect, which can be described as a consequence of a Berry phase. It is also parallel to the propagation direction of a light beam. The imaginary part of the weak value can be used to analyze ultrasmall longitudinal phase shifts in different topological phases. These optical signatures are related to the Chern number and bandgaps; we also use a preselection and postselection technique on the spin state to enhance the original signature. The weak amplification technique offers a potential way to determine the spin and valley properties of charge carriers, Chern numbers, and topological phases by direct optical measurement.

One-step rapid quantification of SARS-CoV-2 virus particles via low-cost nanoplasmonic sensors in generic microplate reader and point-of-care device

The spread of SARS-CoV-2 virus in the ongoing global pandemic has led to infections of millions of people and losses of many lives. The rapid, accurate and convenient SARS-CoV-2 virus detection is crucial for controlling and stopping the pandemic. Diagnosis of patients in the early stage infection are so far limited to viral nucleic acid or antigen detection in human nasopharyngeal swab or saliva samples. Here we developed a method for rapid and direct optical measurement of SARS-CoV-2 virus particles in one step nearly without any sample preparation using a spike protein specific nanoplasmonic resonance sensor. As low as 370 vp/mL were detected in one step within 15 min and the virus concentration can be quantified linearly in the range of 0 to 107 vp/mL. Measurements shown on both generic microplate reader and a handheld smartphone connected device suggest that our low-cost and rapid detection method may be adopted quickly under both regular clinical environment and resource-limited settings.

All-fiber all-optical quantitative polymerase chain reaction (qPCR)

Quantitative polymerase chain reaction (qPCR), the real-time amplification and measurement of a targeted DNA molecule, has revolutionized the biological sciences and is routinely applied in areas such as medical diagnostics, forensics, and agriculture. Despite widescale use of qPCR technology in the lab, the availability of low-cost and high-speed portable systems remains one of the barriers to routine in-field implementation. Here we propose and demonstrate a potential solution using a photonics-based qPCR system. By using an all-optical approach, we achieve ultra-fast temperature response with real-time temperature feedback using nanoliter scale reaction volumes. The system uses a microcavity to act as a nanoliter scale reaction vessel with a laser-driven and optically monitored temperature cycling system for ultrafast thermal cycling and incorporates an all-fiber fluorescence excitation/detection system to achieve real-time, high sensitivity fluorescence monitoring of the qPCR process. Further, we demonstrate the potential of the system to operate as a label-free qPCR system through direct optical measurement of the sample refractive index. Due to advantages in portability and fabrication simplicity, we anticipate that this platform technology will offer a new strategy for fundamental techniques in biochemistry applications, such as point-of-care and remote diagnostics.

Energetics at the Surface: Direct Optical Mapping of Core and Surface Electronic Structure in CdSe Quantum Dots Using Broadband Electronic Sum Frequency Generation Microspectroscopy

Understanding and controlling the electronic structure of nanomaterials is the key to tailoring their use in a wide range of practical applications. Despite this need, many important electronic states are invisible to conventional optical measurements and are typically identified indirectly based on their inferred impact on luminescence properties. This is especially common and important in the study of nanomaterial surfaces and their associated defects. Surface trap states play a crucial role in photophysical processes yet remain remarkably poorly understood. Here we demonstrate for the first time that broadband electronic sum frequency generation (eSFG) microspectroscopy can directly map the optically bright and dark states of nanoparticles, including the elusive below gap states. This new approach is applied to model cadmium selenide (CdSe) quantum dots (QDs), where the energies of surface trap states have eluded direct optical characterization for decades. Our eSFG measurements show clear signatures of electronic transitions both above the band gap, which we assign to previously reported one- and two-photon transitions associated with the CdSe core, as well as broad spectral signatures below the band gap that are attributed to surface states. In addition to the core states, this analysis reveals two distinct distributions of below gap states, providing the first direct optical measurement of both shallow and deep surface states on this system. Finally, chemical modification of the surfaces via oxidation results in the relative increase in the signals originating from the surface states. Overall, our eSFG experiments provide an avenue to directly map the entirety of the QD core and surface electronic structure, which is expected to open up opportunities to study how these materials are grown in situ and how surface states can be controlled to tune functionality.

Changes of particle deposition caused by different breathing patterns during active lung simulation.

Aerosols are an integral part of everyday life and as such are inhaled under various conditions and circumstances. These may vary based on the health and activity status of an individual. The aim of this work is to analyse the particle deposition mechanisms during the simulation of three different breathing patterns using an aerosol representing the PM1 fraction of fine particles. The active electro-mechanical lung simulator xPULM is utilized as a driving force and is combined with a non-invasive direct reading optical aerosol measurement system. Results show differences between the number of deposited particles for the three breathing patterns and for the three typical size ranges of airborne particles. Overall, the presented approach demonstrates the possibility of determining the changes of aerosol uptake based on different breathing patterns using the electro-mechanical lung simulator and laboratory produced aerosols. Further measurement cycles must be performed in order to validate the found interactions and to characterize the major influencing parameters.

High-speed transverse and axial optical force measurements using amplitude filter masks.

Direct optical force measurement is a versatile method used in optical tweezers experiments, providing accurate measurements of forces for a wide range of particles and trapping beams. It is based on the detection of the change of the momentum of light scattered by a trapped object. A digital micromirror device can be used to selectively reflect light in different directions using an appropriately defined mask. We have developed position-sensitive masked detection (PSMD) for measuring transverse (radial) and axial forces. The method is comparable in performance to the fastest split detectors, while maintaining the linearity and customizability similar to duo-lateral position-sensitive detectors (PSD) and cameras. We show an order of magnitude increase in the bandwidth compared to a conventional PSD for radial forces. We measure axial force and verify the measurement using the Stokes drag for the particle. Combining both detectors (PSMD and PSD), we can perform full 3-D optical force measurements in real time.

Intensity‐modulated Sagnac loop temperature sensor setup

AbstractIn this article, the novel low‐cost and simple intensity‐modulated Sagnac loop based temperature sensor setup is presented. The sensor head consists of a short length of polarization‐maintaining fiber (PMF), which is spliced to a single‐mode fiber optic coupler. Due to the short section of PMF, the spectrum has wide separation between adjacent interferometer dips. This idea ensures that transmission of a broadband light source has different losses after propagation through Sagnac loop whether temperature changes and causes shift of interferometer dips. Therefore, tracking of wavelength shift of interferometer dip is not required in this setup as it relies on direct optical power measurement. Instead of using spectral analysis instruments, we present the novel intensity‐modulated optical fiber temperature sensor based on Sagnac loop created of short section of PMF. This particular sensor was experimentally investigated for a temperature range of 25‐50.5°C and exhibited the sensitivity of 0.066 mW/1°C with resolution of 0.34°C. The setup could be easily applied in order to create fiber optic sensor network for temperature monitoring.

Transitional Goos-Hänchen effect due to the topological phase transitions.

We examine the Goos-Hänchen (GH) effect for a Gaussian beam impinging on the surface of silicene whose topological phase transitions can be modulated by external electric field and/or irradiating circular polarized light. It is shown that both the spatial and angular shifts in GH effect present a sharp jump due to the topological phase transitions. The transitional GH effect can be attributed to transitional optical conductivity, which relates to Berry curvature and Chern numbers. These results can be extensively extended to other two-dimensional atomic crystals in graphene family. We believe that the transitional GH effect may offer a possible way to determine the Berry curvature, Chern numbers, and topological phase transition by a direct optical measurement.