Oblique-incidence Reflectivity Difference Research Articles

Label-free OIRD detection of protein microarrays on high dielectric constant substrate with enhanced intrinsic sensitivity

Oblique-incidence reflectivity difference (OIRD) is a dielectric constant-sensitive technique and exhibits intriguing applications in label-free and high-throughput detection of protein microarrays. With the outstanding advantage of being compatible with arbitrary substrates, however, the effect of the substrate, particularly its dielectric constant on the OIRD sensitivity has not been fully disclosed. In this paper, for the first time we investigated the dependence of OIRD sensitivity on the dielectric constant of the substrate under top-incident OIRD configuration by combining theoretical modeling and experimental evaluation. Optical modeling suggested that the higher dielectric constant substrate exhibits a higher intrinsic sensitivity. Experimentally, three substrates including glass, fluorine-doped tin oxide (FTO) and silicon (Si) with different dielectric constants were selected as microarray substrates and their detection performances were evaluated. In good agreement with the modeling, high dielectric constant Si-based microarray exhibited the highest sensitivity among three chips, reaching a detection limit of as low as 5 ng mL−1 with streptavidin as the model target. Quantification of captured targets on three chips with on-chip enzyme-linked immunosorbent assay (ELISA) further confirmed that the enhanced performance originates from the high dielectric constant enhanced intrinsic OIRD sensitivity. This work thus provides a new way to OIRD-based label-free microarrays with improved sensitivity.

Characterizing Edible Oils by Oblique-Incidence Reflectivity Difference Combined with Machine Learning Algorithms.

Due to the significant price differences among different types of edible oils, expensive oils like olive oil are often blended with cheaper edible oils. This practice of adulteration in edible oils, aimed at increasing profits for producers, poses a major concern for consumers. Furthermore, adulteration in edible oils can lead to various health issues impacting consumer well-being. In order to meet the requirements of fast, non-destructive, universal, accurate, and reliable quality testing for edible oil, the oblique-incidence reflectivity difference (OIRD) method combined with machine learning algorithms was introduced to detect a variety of edible oils. The prediction accuracy of Gradient Boosting, K-Nearest Neighbor, and Random Forest models all exceeded 95%. Moreover, the contribution rates of the OIRD signal, DC signal, and fundamental frequency signal to the classification results were 45.7%, 34.1%, and 20.2%, respectively. In a quality evaluation experiment on olive oil, the feature importance scores of three signals reached 63.4%, 18.9%, and 17.6%. The results suggested that the feature importance score of the OIRD signal was significantly higher than that of the DC and fundamental frequency signals. The experimental results indicate that the OIRD method can serve as a powerful tool for detecting edible oils.

Analysis of Fluid Replacement in Two Fluidic Chambers for Oblique-Incidence Reflectivity Difference (OI-RD) Biosensor.

Optical biosensors have a significant impact on various aspects of our lives. In many applications of optical biosensors, fluidic chambers play a crucial role in facilitating controlled fluid delivery. It is essential to achieve complete liquid replacement in order to obtain accurate and reliable results. However, the configurations of fluidic chambers vary across different optical biosensors, resulting in diverse fluidic volumes and flow rates, and there are no standardized guidelines for liquid replacement. In this paper, we utilize COMSOL Multiphysics, a finite element analysis software, to investigate the optimal fluid volume required for two types of fluidic chambers in the context of the oblique-incidence reflectivity difference (OI-RD) biosensor. We found that the depth of the fluidic chamber is the most crucial factor influencing the required liquid volume, with the volume being a quadratic function of the depth. Additionally, the required fluid volume is also influenced by the positions on the substrate surface bearing samples, while the flow rate has no impact on the fluid volume.

Label-Free and Real-Time Optical Detection of Affinity Binding of the Antibody on Adherent Live Cells.

Oblique-incidence reflectivity difference (OIRD) is a novel real-time, label-free, and nondestructive optical detection method and exhibits encouraging application in the detection of antibody/DNA microarrays. In this study, for the first time, an OIRD label-free immunoassay was achieved by using adherent live cells as the probe. The cells were cultured on glass cells, and the affinity binding of antibodies targeted on the HLA class I antigen of the cell surface was detected with an OIRD. The results show that an OIRD is able to detect the binding process of anti-human HLA-A, B, and C antibodies on MDA-MB-231 cells and HUVEC cells. Control experiments and complementary fluorescence analysis confirmed the high detection specificity and good quantitative virtue of the OIRD label-free immunoassay. Label-free OIRD imaging analysis of cell microarrays was further demonstrated successfully, and the underlying optical mechanism was revealed by combining the theoretical modeling. This work explores the use of live cells as probes for an OIRD immunoassay, thus expanding the potential applications of the OIRD in the field of pathological analysis, disease diagnosis, and drug screening, among others.

Detection speed optimization of the OI-RD microscope for ultra-high throughput screening.

The oblique-incidence reflectivity difference (OI-RD) microscope is a label-free detection system for microarrays that has many successful applications in high throughput drug screening. The increase and optimization of the detection speed of the OI-RD microscope will enable it to be a potential ultra-high throughput screening tool. This work presents a series of optimization methods that can significantly reduce the time to scan an OI-RD image. The wait time for the lock-in amplifier was decreased by the proper selection of the time constant and development of a new electronic amplifier. In addition, the time for the software to acquire data and for translation stage movement was also minimized. As a result, the detection speed of the OI-RD microscope is 10 times faster than before, making the OI-RD microscope suitable for ultra-high throughput screening applications.

Polystyrene microsphere monolayer assembled on glass slide for label-free OIRD immunoassay with enhanced sensitivity

Oblique-incidence reflectivity difference (OIRD) is a newly established method to monitor various surface processes and shows great prospect for real-time and label-free immunoassay, yet its sensitivity needs essential improvement to meet the requirement of practical applications. In this work, a label-free OIRD immunoassay biochip was developed with improved sensitivity by using standard glass slide coated with polystyrene (PS) microsphere monolayer as the substrate. The immunoassay sensitivity of this biochip was found to be greatly improved compared with the conventional biochip built on glass slide. Further on-chip ELISA and optical calculation suggests that the improvement is not only associated with high capture efficiency of this biochip towards its target, but is also benefited from the porous PS monolayer enhanced intrinsic OIRD sensitivity via optical interference enhancement and effective dielectric constant effect. This work may provide valuable insight into the development of high performance label-free OIRD bio-detection devices.

In situ probing of wax precipitation of waxy oil using oblique-incidence reflectivity difference at open bulk surface

Considering the negative effects of wax precipitation during petroleum transportation on flow assurance and profit loss, in this study, oblique-incidence reflectivity difference (OIRD) analysis is demonstrated to be a powerful tool for the in situ analysis of wax precipitation. Based on the hybrid detection of waxy oil and natural cooling, we develop a detailed wax precipitation model for waxy oil and demonstrate that it can be used to predict actual precipitation features, which are amenable to experimental validation. The curve trend of the OIRD detection exactly reveals the wax formation process, including nucleation, growth, and crystallization. The efficiency of this technique is proven by the fact that the OIRD signals provide the detailed characteristics of the wax precipitation, which include not only the wax appearance temperature (WAT) but also the rate of change of the crystallization process. The advantage of distinguishing between the different stages of the complex wax crystallization process with time and amplitude is demonstrated.

Optical Detection for the Adsorption Kinetics of Surfactant Solutions on the Surface/Interface: Oblique-Incidence Reflectivity Difference Investigation

The interaction of interfacial molecules was a hot issue in many fields, such as petroleum: the adsorption kinetics process of surfactant molecules on the interface was the key to reduce the dynamic interfacial tension and enhance oil recovery. Since the aggregation behavior of surfactant molecules on the water surface would lead to changes in the dielectric properties of the surface layer, we applied a dielectric detection technology with a vertical resolution of nanometer precision, oblique-incidence reflectivity difference (OIRD) technology, to study the adsorption kinetics of surfactant molecules on the water surface in this article. According to the test results, we established a model of molecular dynamic adsorption and explained its mechanism. This dynamic process could be divided into three stages: micelles dissociated in bulk water, molecules diffused to the subsurface layer, and molecules broke through the adsorption barrier and adsorbed on the water surface. Among them, the diffusion process was in accordance with Fick’s second law, and the process of surfactant molecules being adsorbed from the subsurface to the surface can be described by the Arrhenius formula. This work was not only applicable to the petroleum field to understand the essence of surfactant reducing surface tension but also to help investigate the subject of molecular behavior at the liquid–liquid or gas–liquid interface in other fields.

Oblique-incidence reflectivity difference method combined with deep learning for predicting anisotropy of invisible-bedding shale

Deep learning methodologies have revolutionized prediction in many fields and is potential to do the same in the petroleum industry because of the complex oil–gas reservoir. A limitation remains for dense shale exploration in that the shales with invisible bedding are difficult to characterize measurably because of the considerable complexity of the geological structures. The oblique-incidence reflectivity difference method (OIRD) is sensitive to the surface features and was used to obtain a layered distribution of dielectric properties in shales. In this paper, we report a combination of OIRD and deep learning method to identify the dielectric anisotropy of an invisible-bedding shale. The model performs well and clearly identifies the bedding of the shale based on the output values associated with the probability. Only a single direction was determined to have laminations with widths of 20–60μm. The anisotropy features detected by OIRD also existed in the invisible-bedding shale and were caused by the smaller cracks and denser particles’ orientation relative to general shales. As current dense reservoirs include rich invisible-bedding shales, we believe that the OIRD method combined with deep learning method can help improve the exploration efficiency of shale reservoirs.

Spatially resolved electrochemical reversibility of a conducting polymer thin film imaged by oblique-incidence reflectivity difference.

The spatially resolved electrochemical reversibility of a polyaniline (PANI) thin film is successfully imaged by an oblique-incidence reflectivity difference (OIRD) technique. The electrochemical conversion of the PANI thin film from its completely reduced state to partially oxidized state gives rise to a considerable OIRD signal while upon the deterioration of the electrochemical reversibility, this OIRD signal decreases.

Chip architecture-enabled sensitivity enhancement of oblique-incidence reflectivity difference for label-free protein microarray detection

Oblique-incidence reflectivity difference (OIRD) is a promising optical technique for detection of protein microarray chip with the compelling features of being label-free, real-time, high-throughput and nondestructive, but its sensitivity requires essential improvement for practical applications. In this work we report a simple yet highly efficient strategy to boost the sensitivity of OIRD by rationally engineering the biochip architecture via introducing a polymer film (polydopamine, PDA) to the glass surface. With anti-Zearalenone (ZEN) monoclonal antibody as a model target, up to 2 orders of magnitude sensitivity enhancement was demonstrated on this engineered chip compared to conventional silanized glass chip. Experimental investigation indicates that the OIRD sensitivity is positively correlated to the polymer thickness until reaching the maximal sensitivity at 90.2 nm thickness; a detection limit of as low as 5.0 ng mL−1 is achieved on this optimal chip. Theoretical calculation unveils that the polymer film serves as an interference layer to enhance the light-matter interaction for improved sensitivity, and the OIRD sensitivity possesses a periodic dependence on the film thickness. This work reports for the first time an interference-based versatile strategy to boost OIRD sensitivity and reveals the underlying mechanism, and thus paves a new way toward sensitive and label-free OIRD detection of protein microarrays.

Label-free Microarray-based Binding Affinity Constant Measurement with Modified Fluidic Arrangement

The oblique-incidence reflectivity difference (OI-RD) scanning microscopy has the capability of simultaneously measuring binding curves of a protein probe with tens of thousands molecular targets in a microarray and yielding reaction rate constants. However, the quality of reaction rate constants is influenced by the fluidic system. To improve the quality of reaction rate constant measurement over the entire microarray, we demonstrate a fluidic chamber that allows the fluid to flow from the bottom to the top uniformly across the microarray and thus provides more uniform and accurate measurements of reaction rate constants with simplified fluidic design.

Oblique-incidence reflectivity difference application for morphology detection.

Analogous with scanning electron microscopy, we use an oblique-incidence reflectivity difference (OIRD) approach for morphology detection. By scanning the active carbon clusters in a one-dimensional way and the reservoir rocks in a two-dimensional way, the morphology of the samples' surface can be revealed in OIRD signal images. High OIRD signals of active carbon samples refer to the centralized distribution areas of carbon, and the fluctuations are caused by the uneven distribution of carbon pellets. OIRD intensity is proportional to the thickness of materials. In terms of rocks, the trough areas with smaller values refer to the low-lying fields. The areas with relatively large OIRD intensities correspond to the protuberance areas of rocks. Consequently, OIRD is a sensitive yet rapid measure of surface detection in material and petrogeology science.

Real-time, label-free characterization of oligosaccharide-binding proteins using carbohydrate microarrays and an ellipsometry-based biosensor

ABSTRACTCarbohydrates present on cell surfaces mediate cell behavior through interactions with other biomolecules. Due to their structural complexity, diversity, and heterogeneity, it is difficult to fully characterize a variety of carbohydrates and their binding partners. As a result, novel technologies for glycomics applications have been developed, including carbohydrate microarrays and label-free detection methods. In this paper, we report using the combination of oligosaccharide microarrays and the label-free oblique-incidence reflectivity difference microscopy for real-time characterization of oligosaccharide-binding proteins. Aminated human milk oligosaccharides were immobilized on epoxy-coated glass substrates as microarrays for reactions with Family 1 of solute-binding proteins from Bifidobacterium longum subsp. infantis (B. infantis). Binding affinities of these protein–oligosaccharide interactions showed preferences of Family 1 of solute-binding proteins to host glycans, which helps in characterizing the complex process of human milk oligosaccharides foraging by B. infantis.

Real-time detection of dielectric anisotropy or isotropy in unconventional oil-gas reservoir rocks supported by the oblique-incidence reflectivity difference technique.

Current geological extraction theory and techniques are very limited to adequately characterize the unconventional oil-gas reservoirs because of the considerable complexity of the geological structures. Optical measurement has the advantages of non-interference with the earth magnetic fields, and is often useful in detecting various physical properties. One key parameter that can be detected using optical methods is the dielectric permittivity, which reflects the mineral and organic properties. Here we reported an oblique-incidence reflectivity difference (OIRD) technique that is sensitive to the dielectric and surface properties and can be applied to characterization of reservoir rocks, such as shale and sandstone core samples extracted from subsurface. The layered distribution of the dielectric properties in shales and the uniform distribution in sandstones are clearly identified using the OIRD signals. In shales, the micro-cracks and particle orientation result in directional changes of the dielectric and surface properties, and thus, the isotropy and anisotropy of the rock can be characterized by OIRD. As the dielectric and surface properties are closely related to the hydrocarbon-bearing features in oil-gas reservoirs, we believe that the precise measurement carried with OIRD can help in improving the recovery efficiency in well-drilling process.

Optical Microscopy for Detecting Binding on Small Molecule Microarrays.

Small molecule microarrays (SMMs) have revolutionized parallel screening of multiple biological interactions. SMMs are a high-throughput technique for simultaneous detection of up to thousands of biological interactions. Conventional detection technique employed in SMMs is fluorescence spectroscopy. However, the possibility of fluorescent labels affecting the binding properties of small molecules drives the development of label-free screening techniques. Here, we describe two label-free detection techniques using optical microscopy for the detection of binding on SMMs. The first optical detection technique-ellipsometry, and more specifically, oblique incidence reflectivity difference to study the kinetics of the association between small molecule targets and protein probes is discussed. Then, we describe another optical detection technique-surface plasmon resonance microscopy. The sample preparation steps and protocols of the two techniques to study the interactions between SMMs and their protein targets are elaborated in great detail.

Label-Free Sensing on Microarrays.

Microarrays of biological molecules such as DNAs, proteins, carbohydrates, and small molecules provide a high-throughput platform for screening tens of thousands of biomolecular interactions simultaneously, facilitating the functional characterization of these biomolecules in areas of genomics, proteomics, glycomics, and cytomics. Routinely, analysis of binding reactions between solution-phased probes and surface-immobilized targets involves some kinds of fluorescence-based detection methods. Even though these methods have advantages of high sensitivity and wide dynamic range, labeling probes and/or targets inevitably changes their innate properties and in turn affects probe-target interactions in often uncharacterized ways. Therefore, in recent years, various label-free sensing technologies have been developed for characterizing biomolecular interactions in microarray format. These biosensors, to a certain extent, take the place of fluorescent methods by providing a comparable sensitivity as well as retaining the conformational and functional integrality of biomolecules to be investigated. More importantly, some of these biosensors are capable of real-time monitoring probe-target interactions, providing the binding affinities of these reactions. Using label-free biosensors in microarrays has become a current trend in developing high-throughput screening platforms for drug discoveries and applications in all areas of "-omics." This article is aimed to provide principles and recent developments in label-free sensing technologies applicable to microarrays, with special attentions being paid to surface plasmon resonance microscopy and oblique-incidence reflectivity difference microscopy.

Calibration of oblique-incidence reflectivity difference for label-free detection of a molecular layer.

Oblique-incidence reflectivity difference (OI-RD) is a form of polarization-modulation ellipsometry that measures properties of thin films on a solid surface through the change in polarization state of light upon reflection from the surface. The measurement accuracy depends on the precision of the phase modulation amplitude and azimuthal alignments of key polarizing optical elements and, thus, requires careful calibration. In the present work, we describe robust methods of such calibrations that enable precise determination of the modulation amplitude and static retardation of a phase modulator and azimuths of key polarizing optics in an OI-RD system.

Evaluation of simulated reservoirs by using the oblique-incidence reflectivity difference technique

Evaluation of simulated reservoirs by using the oblique-incidence reflectivity difference technique

Label-Free Real-Time Monitoring of Reactions Between Internalin A and Its Antibody by an Oblique-Incidence Reflectivity-Difference Method

Surface protein internalin (InlA) is a major virulence factor of the food-borne pathogen L. monocytogenes. It plays an important role in bacteria crossing the host's barrier by specific interaction with the cell adhesion molecule E-cadherin. Study of this protein will help to find better ways to prevent listeriosis. In this study, a monoclonal antibody against InlA was used to detect InlA. The reaction was label-free and monitored in real time with an oblique-incidence reflectivity-difference (OI-RD) technique. The kinetic constants k on and k off and the equilibrium dissociation constant K d for this reaction were also obtained. These parameters indicate that the antibody is capable of detecting InlA. Additionally, the results also demonstrate the feasibility of using OI-RD for proteomics research and bacteria detection.