High-resolution Optical Technique Research Articles

Sensing Biomolecules Associated with Cells' Radiosusceptibility by Advanced Micro- and Nanospectroscopy Techniques.

Radiotherapy is one of the most common approaches for cancer treatment, especially in the case of peripheral nervous system tumors. As it requires exposure to high doses of ionizing radiation, it is important to look for substances that support efficient reduction of the tumor volume with simultaneous prevention of the surrounding noncancerous cells. Cannabidiol (CBD), which exhibits both anticancer and neuroprotective properties, was applied as a potential modulator of radiological response; however, its influence on cells undergoing irradiation remains elusive. Here, we have applied high-resolution optical spectroscopy techniques to capture biomolecules associated with CBD shielding of normal and damaging cancerous cells upon X-ray exposure. Conventional Raman (RS) and Fourier transformed infrared (FT-IR) spectroscopies provided semiquantitative information mainly about changes in the concentration of total lipids, DNA, cholesteryl esters, and phospholipids in cells. A through assessment of the single cells by atomic force microscopy coupled with infrared spectroscopy (AFM-IR) allowed us to determine not only the alterations in DNA content but also in its conformation due to cell treatment. Pronounced nanoscale changes in cholesteryl ester metabolites, associated with CBD treatment and radiation, were also observed. AFM-IR chemoselective maps of the single cells indicate the modified distribution of cholesteryl esters with 40 nm spatial resolution. Based on the obtained results, we propose a label-free and fast analytical method engaging optical spectroscopy to assess the mechanism of normal and cancerous cell susceptibility to ionizing radiation when pretreated with CBD.

Bubble departure and sliding in high-pressure flow boiling of water

Bubble growth, departure and sliding in low-pressure flow boiling has received considerable attention in the past. However, most applications of boiling heat transfer rely on high-pressure flow boiling, for which very little is known, as experimental data are scarce and very difficult to obtain. In this work, we conduct an experiment using high-resolution optical techniques. By combining backlit shadowgraphy and phase-detection imaging, we track bubble shape and physical footprint with high spatial ( $6\,\mathrm {\mu }{\rm m}$ ) and temporal ( $33\,\mathrm {\mu }{\rm s}$ ) resolutions, as well as bubble size and position as bubbles nucleate and slide on top of the heated surface. We show that at pressures above 1 MPa bubbles retain a spherical shape throughout the growth and sliding process. We analytically derive non-dimensional numbers to correlate bubble velocity and liquid velocity throughout the turbulent boundary layer and predict the sliding of bubbles on the surface, solely from physical properties and the bubble growth rate. We also show that these non-dimensional solutions can be leveraged to formulate elementary criteria that predict the effect of pressure and flow rate on bubble departure diameter and growth time.

Nanoscale and ultrafast in situ techniques to probe plasmon photocatalysis

Plasmonic photocatalysis uses the light-induced resonant oscillation of free electrons in a metal nanoparticle to concentrate optical energy for driving chemical reactions. By altering the joint electronic structure of the catalyst and reactants, plasmonic catalysis enables reaction pathways with improved selectivity, activity, and catalyst stability. However, designing an optimal catalyst still requires a fundamental understanding of the underlying plasmonic mechanisms at the spatial scales of single particles, at the temporal scales of electron transfer, and in conditions analogous to those under which real reactions will operate. Thus, in this review, we provide an overview of several of the available and developing nanoscale and ultrafast experimental approaches, emphasizing those that can be performed in situ. Specifically, we discuss high spatial resolution optical, tip-based, and electron microscopy techniques; high temporal resolution optical and x-ray techniques; and emerging ultrafast optical, x-ray, tip-based, and electron microscopy techniques that simultaneously achieve high spatial and temporal resolution. Ab initio and classical continuum theoretical models play an essential role in guiding and interpreting experimental exploration, and thus, these are also reviewed and several notable theoretical insights are discussed.

Towards phase-based defect detection: A feasibility study in vibrating panels

This work discusses the possibility of using phase-based motion magnification as a non-destructive inspection tool for defect detection and identification in vibrating panels. Phase-based motion magnification has recently emerged as a potentially disruptive technology in the field of optical methods for vibration engineering. In fact, the method allows to post-process high-speed video recordings in order to magnify small motions happening in a prescribed bandwidth. In particular, our strategy relies on measuring the full-field low-frequency eigen-shapes, and extracting their aberration as resulting from small defects. Effects of defects are usually very localized in space but may appear even at lower frequencies, making the approach particularly suitable for any kind of high-resolution full-field optical technique. Within this work, a novel phase-based processing pipeline for defect detection is described, and a set of preliminary tests is discussed to assess the feasibility and advantages of the methodology. All validations were carried out by means of numerical simulations relying upon a photo-realistic dynamic finite element model of a rectangular plate.

Advancement on optical methods in stress dead-zone characterisation and SIF evaluation

The work described in this paper is a study of the stress dead zone (SDZ) concept with advanced full-field optical methods. The SDZ is a region located around the fatigue crack flanks, adding a negligible contribution to internal stresses on the global deformation energy calculation. In the analytical modelling, this area can be removed from the structural member, resulting in a geometry simplification, and in the possibility of using analytical formulations in the Stress Intensity Factor (SIF) calculation associated to the existing fatigue crack. In a fatigue-testing program, aluminium middle tension (MT) specimens were prepared and then subjected to a cyclic fatigue loading, in order to generate different crack lengths for each specimen. Then, the fatigued specimens are monotonically tested under a uniaxial tensile loading to assess the SDZ concept.The experimental data is collected and analysed through two full-field high-resolution optical techniques with different system resolutions, Digital Image Correlation (DIC), and Electronic Speckle Pattern Interferometry (ESPI). As a result, the SDZ is geometrically characterized through a set of mathematical formulations based on the compliance function for the studied specimens, and is experimentally identified through deformation fields obtained from both DIC and ESPI techniques. The obtained results from both high-resolution methods verify the validity of the concept and demonstrate that it can be used to simplify the analysis.

Electronic Speckle Pattern Interferometry for fatigue crack monitoring

This study aims to monitor the fatigue crack tip through a contactless optical method. A Middle Tension (MT) specimen is initially prepared by submitted it to a cyclic fatigue loading, in order to generate a crack with a specified length. Then, the cracked specimen is statically loaded under a uniaxial tensile condition, and Electronic Speckle Pattern Interferometry (ESPI) is employed to monitor the crack tip. During specimen loading with incremental force values, the behavior of the cracked area is monitored, with displacement and deformation fields acquired for each load increment. The obtained data is used to calculate fracture parameters, such as the Stress Intensity Factor (SIF). For that purpose, an overdeterministic algorithm was developed to calculate SIFs for each measured crack length. The main contribution of the present work is the adoption of a high-resolution optical contactless technique to monitor the fatigue crack tip. The obtained SIF values are compared to the reference solution proposed by ASTM E647 and an acceptable agreement has been verified.

Real-Time Cerebral Vessel Segmentation in Laser Speckle Contrast Image Based on Unsupervised Domain Adaptation.

Laser speckle contrast imaging (LSCI) is a full-field, high spatiotemporal resolution and low-cost optical technique for measuring blood flow, which has been successfully used for neurovascular imaging. However, due to the low signal–noise ratio and the relatively small sizes, segmenting the cerebral vessels in LSCI has always been a technical challenge. Recently, deep learning has shown its advantages in vascular segmentation. Nonetheless, ground truth by manual labeling is usually required for training the network, which makes it difficult to implement in practice. In this manuscript, we proposed a deep learning-based method for real-time cerebral vessel segmentation of LSCI without ground truth labels, which could be further integrated into intraoperative blood vessel imaging system. Synthetic LSCI images were obtained with a synthesis network from LSCI images and public labeled dataset of Digital Retinal Images for Vessel Extraction, which were then used to train the segmentation network. Using matching strategies to reduce the size discrepancy between retinal images and laser speckle contrast images, we could further significantly improve image synthesis and segmentation performance. In the testing LSCI images of rodent cerebral vessels, the proposed method resulted in a dice similarity coefficient of over 75%.

Studying ion channel conformation dynamics by encoding coumarin as unnatural amino acid.

Monitoring the conformational changes of proteins is critical to understand their function. Ion channels are membrane-bound minute machines controlling the passage of ions across biological membranes. The precise labeling of ion channels with fluorescent probes allows studying their dynamics and facilitates their characterization by high-resolution optical techniques. Here we describe a protocol for the use of a small fluorescent reporter, incorporated by expansion of the genetic code in the host cell. An important advantage of using small probes is that they are less likely to perturb protein structure, function, and trafficking. In our hands, Tyr-coumarin proved to be useful to measure the conformational changes occurring in the narrow space of the permeation pathway in single capsaicin receptors. The method described here could be directly translated to the study of membrane receptors, non-electrogenic transporters, or membrane-bound enzymes.

High-accuracy simultaneous measurement of surface profile and film thickness using line-field white-light dispersive interferometer

White-light dispersive interferometry (WLDI) is an instantaneous, high-resolution optical metrological technique for measuring precise and complicated surfaces. This method enables nondestructive inspection of transparent-film-structure devices that are widely used in semiconductor packaging. We propose in this paper to use a home-built WLDI system with line-by-line spectral calibration, phase-shifting algorithm, and single-wave-number method for high-accuracy, simultaneous measurements of surface profiles and film thickness. By calibrating the relationship between wave-number and pixel position on each line of a two-dimensional detector, the line-by-line calibration method improves the measurement accuracy by correcting the spectral distortion caused by the optical system. Moreover, the spectral signal phase is obtained by the phase-shifting algorithm instead of by the Fourier transform method. The single-wave-number method is applied to the computation process by introducing the fringe order, and the measurement result indicates that it enhances the system immunity to environmental noise. A 1.806-µm-high standard step and a 1052.2-nm-thick standard film are measured to verify the system performance and show that the system is highly accurate and reliable.

Video-based assessment of drug-induced effects on contractile motion properties using human induced pluripotent stem cell-derived cardiomyocytes

IntroductionDrug-induced inotropic change is a risk factor in drug development; thus, de-risking is desired in the early stages of drug development. Unlike proarrhythmic risk assessment using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), few in vitro models were validated to predict cardiac contractility. Motion field imaging (MFI), a high-resolution block matching-based optical flow technique, was expected to possess high quantitative predictivity in the detection of contraction speed. We aimed to establish an in vitro model to assess drug-induced contractile changes using hiPSC-CMs and MFI. MethodsMFI was designed to noninvasively characterize cardiomyocyte contractile behavior by analyzing light microscope video images, and maximum contraction speed (MCS) was used as the index of contractility. Using MFI, 9 inactive compounds, 10 negative inotropes, and 10 positive inotropes were tested. Two negative chronotropes, ZD7288 and ivabradine, were also tested. To determine the sensitivity and specificity of the assay, the minimum effective concentration of the MCS was compared with the human effective total therapeutic concentration for 28 compounds in clinical use. ResultsFor 8 negative and 8 positive inotropes, the effects observed in in vivo and clinical studies were detected in MFI assay. MFI assay showed negative chronotropic changes without inotropic changes. MFI assay presented sufficient specificity (83%) and sensitivity (88%), and RNA-sequence analysis provided an insight into the relationship between occurrence of the false compounds and target gene expression. DiscussionWe demonstrated the utility of MFI assay using hiPSC-CMs to assess drug-induced contractile function. These results will facilitate the de-risking of compounds during early drug development.

A prototype system of portable laser speckle imager based on embedded graphics processing unit platform.

Laser speckle contrast imaging (LSCI) is a high-resolution full-field optical technique for measuring blood flow, which has been widely used in clinical and biomedical research. However, most of the current LSCI instruments are bulky, limiting their application settings. In this work, we proposed a prototype system of portable laser speckle imager. Different from the desktop laser speckle systems that utilize personal computer (PC), our system was designed with embedded GPU system (Jetson TX2, NVIDIA, USA) and a LCD touch screen (16.5 × 12.4 cm in size, 380 g in weight). In-vivo experiments showed that the portable GPU-based system had comparable performance with our laboratory LSCI system. Such a portable LSCI imager could be potentially used in a situation that requires for easy operation and installation, such as intraoperative monitoring or bedside diagnosis.

Electrodynamics of granular aluminum from superconductor to insulator: Observation of collective superconducting modes

We report on a detailed study of the optical response and $T_c-\rho$ phase diagram ($T_c$ being the superconducting critical temperature and $\rho$ the normal state resistivity of the film) of granular aluminum, combining transport measurements and a high resolution optical spectroscopy technique. The $T_c-\rho$ phase diagram is discussed as resulting from an interplay between the phase stiffness, the Coulomb repulsion and the superconducting gap $\Delta$. We provide a direct evidence for two different types of well resolved sub-gap absorptions, at $\omega_1\simeq\Delta$ and at $\Delta\lesssim\omega_2\lesssim2\Delta$ (decreasing with increasing resistivity).

High Resolution Surface Metrology Using Microsphere‐Assisted Interference Microscopy

The authors review some of the latest results of a new high resolution optical metrology technique using small glass microspheres placed on the sample to enhance the lateral resolution in optical microscopy. Experimental results are shown of high resolution 2D images of gratings and microelectronic structures. The results of simulations and experimental measurements for 2D imaging through glass microspheres show an increase in magnification of 3–5 times and a lateral resolution as small as 100 nm in air. Experimental results are also shown of 3D measurements of different nanostructures using microspheres that have successfully been incorporated into Mirau and Linnik type interferometers. Results are shown on grooves in Blu‐Ray discs, narrow etched gratings in Si, nanotextured stainless steel surfaces, and on Ag nanodots. Measurements using SEM and AFM are given for comparison. Some of the artefacts and sources of errors in the microsphere‐assisted measurements are presented and discussed. The authors thus demonstrate that microsphere‐assisted interference microscopy is a promising new optical tool for nanometrology.

A Phase Compensation Method for Phase Extraction of Abrupt Surfaces in Projection Moiré

Projection moire method is a high-resolution, non-contacting and full-field optical measurement technique. But the 2π-ambiguity problem in phase unwrapping limits the phase difference between neighbouring pixels under π which makes projection moire method ineffective at measuring abrupt surfaces or steps. This paper aims at putting forward a phase compensation method to solve this 2π-ambiguity problem in projection moire. Since the phase of moire pattern is the variance between the phase of specimen grating on object’s surface and the phase of the reference grating, our method is to calculate the phases of specimen grating and the reference grating respectively, regard their difference as the phase of the moire pattern in theory and correct the wrong unwrapped moire fringe phase with integral multiple of 2π. In order to acquire the phase of specimen grating which also has the 2π-ambiguity problem, using multiple fringe pictures with different pitches. The experiments successfully reconstruct two objects with discontinuities in their surfaces. This phase compensation technique no longer requires us to count fringe orders or find a reference point to mark the zero-order moire fringe during experiments.

STUDIES OF THE MORPHOLOGY OF WATERPROOF COATINGS BASED ON URETHANE ISOCYANATE, ALKYL-PHENOL-FORMALDEHYDE RESIN AND DIBUTYLTIN DILAURATE USING THE HIGH-RESOLUTION OPTICAL MICROSCOPY TECHNIQUE

A study of the morphology and structure of waterproof film coatings based on polyurethane isocyanate, alkyl-phenol-formaldehyde resin and dibutyltin dilaurate with finely dispersed iron-oxide filler depending on their production method (solution method or melting method) using the high-resolution optical microscopy technique was carried out. When obtaining polymer composites (films), the authors varied the ratio between the main components of the polymer matrix, urethane isocyanate and phenol-formaldehyde resin (1:2 or 1:3), and the content of the finely dispersed iron-oxide filler in relation to the polymer binding medium (0.1, 0.6 and 1.2 wt%). In the modes of bright field, phase contrast and crossed nicols, the homogeneity of the obtained films, their structure, aggregation capacity and distribution uniformity of the powdered iron-oxide filler as a part of the polymer matrix, were investigated. The obtained composite material in the form of film coating or adhesive repair compound can be used for waterproofing, repairs and corrosion protection as film coatings of water and underwater hydraulic structures.

INFLUENCIA DE LA DISPERSIÓN DE NANOTUBOS DE CARBONO EN LA DETECCIÓN DE OZONO

Carbon nanotubes (CNT) are promising material to be used as sensitive materials in the gas detection. One disadvantage is their insolubility in different media which limits their performance and processing. By employing techniques not covalent with surfactants is possible increase dispersion of CNT. This article reports the results found in the detection of ozone using pristine multi-walled carbon nanotubes dispersed in three different media: deionized water, methanol and glycerol. Materials dispersed in deionized water exhibited a zero detection of ozone at different concentrations studied. In comparison, electronic devices where sensitive materials were dispersed with methanol and glycerol showed a change in resistance depending on concentration and operating temperature evaluated. The best response was found to be at high temperatures (120 -200 °C). The materials have been characterized by high resolution transmission electron microscopy and optical microscopy technique

Potential for external reinforcement of insulated rail joints

This paper aims to investigate the alternative ways of reducing the deterioration and failure of insulated rail joints of railway tracks. Joints deteriorate faster than rails due to the presence of structural discontinuity. This weakness results in extra displacement due to the applied load and dynamic force that results as a consequence. Overtime, this situation worsens as the impacts and applied stresses damage and soften the ballast and the supporting subgrade under the joint. This study initially presents a static finite element model designed to simulate the mechanics of insulated rail joints, and then a comparison is made between the plain rail and a suspended insulated rail joint under various support stiffnesses. The product design options of the reinforced insulated rail joints are then chosen as input variables of the model. The results of the model are compared with the field and laboratory data acquired via the Video Gauge, which is a new high-resolution optical measurement technique. The results show that the use of strap rails or more robust I-beam sections in the vicinity of the insulated rail joint to stiffen the support structure can significantly reduce the displacement and the subsequent dip angle seen in an insulated rail joint. This potentially presents a means of improving the behaviour of the insulated rail joints. Their impact becomes more significant for soft support conditions. Although these results are indicative of new conditions for insulated rail joints, the field measurements indicate that the magnitude of deflection of insulated rail joints is a result of the structural discontinuity of the rails, the dynamic P2 force, the wheel condition, the degraded ballast and it significantly increases with time under repeated load. Thus, it is recommended that a careful field implementation and testing will indicate the effect of an external enhancement on the timely degradation of insulated rail joints.

Dynamic sinking behaviour in marine phytoplankton: rapid changes in buoyancy may aid in nutrient uptake.

Phytoplankton sinking is an important property that can determine community composition in the photic zone and material loss to the deep ocean. To date, studies of diatom suspension have relied on bulk measurements with assumptions that bulk rates adequately capture the essential characteristics of diatom sinking. However, recent work has illustrated that individual diatom sinking rates vary considerably from the mean bulk rate. In this study, we apply high-resolution optical techniques, individual-based observations of diatom sinking and a recently developed method of flow visualization around freely sinking cells. The results show that in both field samples and laboratory cultures, some large species of centric diatoms are capable of a novel behaviour, whereby cells undergo bursts of rapid sinking that alternate with near-zero sinking rates on the timescales of seconds. We also demonstrate that this behaviour is under direct metabolic control of the cell. We discuss these results in the context of implications for nutrient flux to the cell surface. While nutrient flux in large diatoms increases during fast sinking, current mass transport models cannot incorporate the unsteady sinking behaviour observed in this study. However, large diatoms appear capable of benefiting from the enhanced nutrient flux to their surface during rapid sinking even during brief intervening periods of near-zero sinking rates.

Fast Membrane Dynamics in Planar Suspended Lipid Bilayers Revealed by Single Particle Tracking

The lateral organization, dynamics, and curvature of the plasma membrane are controlled by complex interactions between lipids, proteins, and carbohydrates. Artificial membranes composed of synthetic lipids enable the testing the fundamental membrane properties, such as lipid mobility, phases, and curvature. Supported lipid bilayers are frequently used and provide replication of many important membrane properties. However, their applicability to study lipid phase dynamics and membrane curvature is limited due to the interactions between the membrane and its substrate. To expand the capabilities of artificial membranes, we developed a suspended lipid bilayer system for the planar observation of phase transition and single particle tracking (SPT) via high resolution optical microscopy. The suspended lipid bilayers were created on readily available copper meshes by the fusion of giant unilamellar vesicles to the mesh. With openings of > 200 μm in the mesh, large regions of membrane are available for long-duration SPT and assorted additional membrane perturbations (i.e., physically induced curvature). SPT of fluorescent nanoparticles bound with NeutrAvidin-biotin linkage to the lipids and fast lipid phase dynamics demonstrated the high mobility within the membrane and the benefits of suspending the bilayer above the substrate. The mobility of a 200 nm diameter nanoparticle bound to the suspended lipid bilayer was 1.2 ± 0.3 μm2/s. In future experiments, curvature will be created in the suspended lipid bilayer by physical pushing and pulling on the membrane with an adapted atomic force microscope cantilever to reveal the effects of curvature on nanoscale curvature lipid mobility and lipid phase transitions. The use of this suspended lipid bilayer will have diverse applications in membrane biophysical research and facilitate the study membrane processes with high resolution optical techniques while eliminating the substrate interactions with the membrane.

Probing the the Glass Transition of Atactic Polystyrene Thin Films Using Fiber Optic Refractometry

SummaryAn high resolution optical technique based on the film fiber optic refractometer has been used to investigate the effect of the thickness on the glass transition dynamic of Atactic Polystyrene films in the range 20–120 nm. The thermo‐optic behavior of a set of layers dip coated onto the fiber has been analyzed upon cooling from long term equilibrated melt state. The glassy transition temperature is observed to be thickness‐independent as did both the width and the lower and upper bounds of the transition itself. At lowering the thickness of the film the relevant effect is the reduction of the “contrast” between the melt equilibrium phase and the glassy state. A double layers model where a surface soft layer (3.9 nm at 418 K) do not contribute to the glass dynamic retaining liquid features even at temperature well below the glass transition, while the core layer shows a bulk glass transition, is able to quantitatively reproduce reflectance experimental data.