Simple Optical Methods Research Articles

Coupling digital microfluidics with mass spectrometry

AbstractDigital microfluidics enables the electrical actuation of microliter‐sized droplets on a planar surface, facilitating precise control and digitization of chemical processes. It is typically operated in a closed chip format, preventing evaporation and contamination which also complicates chemical analysis of the trapped droplets. Thus, subsequent analytics are usually carried out offline or with simple optical methods. A new method including a chip‐integrated microspray hole now allows on‐the‐fly mass spectrometry analysis on a digital microfluidics chip.

PH-Dependent HEWL-AuNPs Interactions: Optical Study.

Optical methods (spectroscopy, spectrofluorometry, dynamic light scattering, and refractometry) were used to study the change in the state of hen egg-white lysozyme (HEWL), protein molecules, and gold nanoparticles (AuNPs) in aqueous colloids with changes in pH, and the interaction of protein molecules with nanoparticles was also studied. It was shown that changing pH may be the easiest way to control the protein corona on gold nanoparticles. In a colloid of nanoparticles, both in the presence and absence of protein, aggregation-deaggregation, and in a protein colloid, monomerization-dimerization-aggregation are the main processes when pH is changed. A specific point at pH 7.5, where a transition of the colloidal system from one state to another is observed, has been found using all the optical methods mentioned. It has been shown that gold nanoparticles can stabilize HEWL protein molecules at alkaline pH while maintaining enzymatic activity, which can be used in practice. The data obtained in this manuscript allow for the state of HEWL colloids and gold nanoparticles to be monitored using one or two simple and accessible optical methods.

Nanodroplet wetting and electrowetting behavior on liquid-infused surfaces: A molecular simulation study

Due to the block of the lubricant on liquid-infused surfaces (LISs), the molecular processes near the liquid-liquid interface and the shape ofdropletunderelectrowetting actuation are still difficult to observe with simple optical methods. Molecular dynamics (MD) simulation provides a visual method for observing the nanodroplet morphology on the LISs. In this paper, the impacts of the substrate characteristics and the lubricant thickness on the cloaking state, the wetting state and the diffusion diameter of nanodroplet were studied by the MD simulation. It is found the coating film of the nanodroplet increases with the lubricant layer thickness on the LISs of silicon nanopillarsubstrate, while the nanodroplet is always in the not cloaking state on the LISs of copper nanopillarsubstrate, even with a very thick lubricant layer. Subsequently, the electrowetting behaviors of the nanodroplet under the external electric field in the parallel and perpendicular directions to the surface were studied. The results indicate the droplet changes from the Cassie state to the partial Wenzel state under the influence of the external electric field on the LISs of both substrates. Meanwhile, the coating film thickness increases with the electric field intensity, the nanodroplet changes from a not cloaking state to a cloaking state on the LISs of copper substrate, while still is in a not cloaking state on the LISs of silicon substrate. Compared to the LISs of the silicon substrate, the electro-stretching is easier to happen on the LISs of the copper substrate. Finally, the impact of lubricant layer thickness on the nanodroplet electrowetting was studied on both copper and silicon substrates. It is found the reduction of nanodroplet apparent contact angle increases with the lubricant layer thickness under an external parallel electric field, while it has a maximum on the moderate lubricant thickness under an external electric field in a perpendicular upward or downward direction. Our results indicate the droplet deformation on LISs under the external electric field is contributed to the competition of the electrowetting, the electro-stretching, and the pinning effect.

Hybrid confocal fluorescence and photoacoustic microscopy for the label-free investigation of melanin accumulation in fish scales

Lower vertebrates, including fish, can rapidly alter skin lightness through changes in melanin concentration and melanosomes’ mobility according to various factors, which include background color, light intensity, ambient temperature, social context, husbandry practices and acute or chronic stressful stimuli. Within this framework, the determination of skin chromaticity parameters in fish species is estimated either in specific areas using colorimeters or at the whole animal level using image processing and analysis software. Nevertheless, the accurate quantification of melanin content or melanophore coverage in fish skin is quite challenging as a result of the laborious chemical analysis and the typical application of simple optical imaging methods, requiring also to euthanize the fish in order to obtain large skin samples for relevant investigations. Here we present the application of a novel hybrid confocal fluorescence and photoacoustic microscopy prototype for the label-free imaging and quantification of melanin in fish scales samples with high spatial resolution, sensitivity and detection specificity. The hybrid images are automatically processed through optimized algorithms, aiming at the accurate and rapid extraction of various melanin accumulation indices in large datasets (i.e., total melanin content, melanophores’ area, density and coverage) corresponding to different fish species and groups. Furthermore, convolutional neural network-based algorithms have been trained using the recorded data towards the classification of different scales’ samples with high accuracy. In this context, we demonstrate that the proposed methodology may increase substantially the precision, as well as, simplify and expedite the relevant procedures for the quantification of melanin content in marine organisms.

Table model and portable optical sensors for the monitoring of time-dependent liquid spreading over rough surfaces

BackgroundMany applications require liquids to efficiently wet required surfaces as it denotes better performance. The dynamics of pure and complex liquid is known to influence the spreading properties; however, this influence is less understood and solicits other measuring techniques to elucidate the grey area. In this work, we demonstrate the use of simple yet novel optical methods in the monitoring of liquid spreading of pure diesel and kerosene and their binary (complex) mixtures.MethodsThe optical devices are a table model and portable optical sensors which use a diffractive optical element for filtering the specular reflection from a laser speckle pattern obtained from the liquid spreading on the rough surface-liquid-air system. The surfaces used in this study were metal surface roughness standards and roughened glass surface. The viability of the devices was demonstrated using two liquids, namely diesel oil and kerosene, that have a wide difference in their contact angles. The performance of the devices was further tested using binary mixtures of the diesel oil and kerosene. Based on the scattering properties of the spreading liquids and the surfaces, the time-dependent signal was measured with the optical devices.ResultsIt was observed that the spreading was influenced by the surface roughness. The magnitude of the signal decreased with increased surface roughness indicating less variation in the spreading of the liquid drop with the increased surface roughness. The nature of the detected signal for the kerosene on the surface with roughness values below the wavelength of the device follows the Tanner’s law of drop spreading. However, the diesel spreads at a lower rate. Additionally, the complexity of the internal interaction of the diesel-kerosene binary mixtures leads to a complex spreading mechanism on the solid surfaces allowing us to screen the adulterated liquids from the authentic diesel oil with high reliability.ConclusionWe have introduced two novel optical sensors (table model and portable) for the detection of the changes in liquid drop spreading over rough surfaces. The spreading of the liquid drops over a rough surface causes a local contact angle that experiences hysteresis during the spreading process. The spreading depends on the complexity of the liquid and the magnitude of the surface roughness. The unique configuration of the devices makes the portable sensor suitable for longer duration measurements and for field applications, whilst the table model is best suited for monitoring the first transient moments of liquid spreading and for laboratory applications. Such spreading techniques can also be utilized in the detection of wine and strong alcohol, such as vodka, adulterations with glycol and water, respectively.

The simple optical methods for early diagnosis of selected benign and malignant brain tumors of human

The optical properties of benign and malignant human brain tumors were investigated to provide a new diagnosis method. We studied various samples of adult human brain tissue (male and female) in two linear (by Optical density) and nonlinear (by Z-scan method) regimes. The obtained experimental results show that optical density for malignant is more than benign tissues and the nonlinear behavior of benign and malignant tissues are completely different because the nonlinear refractive index had a negative sign for benign tumor and a positive sign for malignant tumor. Results can be used for diagnosis between benign and malignant brain tissue.

Nondestructive Thickness Mapping of Wafer-Scale Hexagonal Boron Nitride Down to a Monolayer.

The availability of an accurate, nondestructive method for measuring thickness and continuity of two-dimensional (2D) materials with monolayer sensitivity over large areas is of pivotal importance for the development of new applications based on these materials. While simple optical contrast methods and electrical measurements are sufficient for the case of metallic and semiconducting 2D materials, the low optical contrast and high electrical resistivity of wide band gap dielectric 2D materials such as hexagonal boron nitride (hBN) hamper their characterization. In this work, we demonstrate a nondestructive method to quantitatively map the thickness and continuity of hBN monolayers and bilayers over large areas. The proposed method is based on acquisition and subsequent fitting of ellipsometry spectra of hBN on Si/SiO2 substrates. Once a proper optical model is developed, it becomes possible to identify and map the commonly observed polymer residuals from the transfer process and obtain submonolayer thickness sensitivity for the hBN film. With some assumptions on the optical functions of hBN, the thickness of an as-transferred hBN monolayer on SiO2 is measured as 4.1 Å ± 0.1 Å, whereas the thickness of an air-annealed hBN monolayer on SiO2 is measured as 2.5 Å ± 0.1 Å. We argue that the difference in the two measured values is due to the presence of a water layer trapped between the SiO2 surface and the hBN layer in the latter case. The procedure can be fully automated to wafer scale and extended to other 2D materials transferred onto any polished substrate, as long as their optical functions are approximately known.

An automated method to evaluate the enzyme kinetics of β-glucosidases.

Enzyme kinetic measurements are important for the characterization and engineering of biocatalysts, with applications in a wide range of research fields. The measurement of initial reaction velocity is usually slow and laborious, which motivated us to explore the possibilities for automating this process. Our model enzyme is the maize β-glucosidase Zm-p60.1. Zm-p60.1 plays a significant role in plant growth and development by regulating levels of the active plant hormone cytokinin. Zm-p60.1 belongs to a wide group of hydrolytic enzymes. Members of this group hydrolyze several different types of glucosides, releasing glucose as a secondary product. Enzyme kinetic measurements using artificial substrates are well established, but burdensome and time-consuming. Thus, they are a suitable target for process automation. Simple optical methods for enzyme kinetic measurements using natural substrates are often impossible given the optical properties of the enzymatic reaction products. However, we have developed an automated method based on glucose detection, as glucose is released from all substrates of glucosidase reactions. The presented method can obtain 24 data points from up to 15 substrate concentrations to precisely describe the enzyme kinetics. The combination of an automated liquid handling process with assays that have been optimized for measuring the initial hydrolysis velocity of β-glucosidases yields two distinct methods that are faster, cheaper, and more accurate than the established protocols.

PLASTER ANALYSIS AND THE LIFE HISTORY OF A STRUCTURE: DEMONSTRATED AT THE EXAMPLE OF HOMOL’OVI I IN NORTHEASTERN ARIZONA

Multiple plaster layers are found on the walls, in niches, and on other features of many structures in the Pueblo Southwest, as well as in many other regions of the world. In previous studies these plaster layers were primarily examined in association with the analysis of wall paintings, such as the colorful and highly evolved kiva mural decoration at several Pueblo IV sites, but not independently of wall paintings. In this research, plaster layers are defined as intentional wall decorations with distinctive and important visual performance characteristics. Simple optical plaster analyses methods, applicable even in a field setting, can enrich archaeological interpretation of structures and entire sites. At the structural level, plaster analysis data can establish the structure’s life history and assist in relative dating of features added or sealed within the original structure. At the site level, data can reveal information about socioeconomic changes through time. The current research illustrates the importance of plaster analysis using data gathered at the ancestral Hopi site of Homol’ovi I.

Practical considerations for conducting ecotoxicity test methods with manufactured nanomaterials: what have we learnt so far?

This review paper reports the consensus of a technical workshop hosted by the European network, NanoImpactNet (NIN). The workshop aimed to review the collective experience of working at the bench with manufactured nanomaterials (MNMs), and to recommend modifications to existing experimental methods and OECD protocols. Current procedures for cleaning glassware are appropriate for most MNMs, although interference with electrodes may occur. Maintaining exposure is more difficult with MNMs compared to conventional chemicals. A metal salt control is recommended for experiments with metallic MNMs that may release free metal ions. Dispersing agents should be avoided, but if they must be used, then natural or synthetic dispersing agents are possible, and dispersion controls essential. Time constraints and technology gaps indicate that full characterisation of test media during ecotoxicity tests is currently not practical. Details of electron microscopy, dark-field microscopy, a range of spectroscopic methods (EDX, XRD, XANES, EXAFS), light scattering techniques (DLS, SLS) and chromatography are discussed. The development of user-friendly software to predict particle behaviour in test media according to DLVO theory is in progress, and simple optical methods are available to estimate the settling behaviour of suspensions during experiments. However, for soil matrices such simple approaches may not be applicable. Alternatively, a Critical Body Residue approach may be taken in which body concentrations in organisms are related to effects, and toxicity thresholds derived. For microbial assays, the cell wall is a formidable barrier to MNMs and end points that rely on the test substance penetrating the cell may be insensitive. Instead assays based on the cell envelope should be developed for MNMs. In algal growth tests, the abiotic factors that promote particle aggregation in the media (e.g. ionic strength) are also important in providing nutrients, and manipulation of the media to control the dispersion may also inhibit growth. Controls to quantify shading effects, and precise details of lighting regimes, shaking or mixing should be reported in algal tests. Photosynthesis may be more sensitive than traditional growth end points for algae and plants. Tests with invertebrates should consider non-chemical toxicity from particle adherence to the organisms. The use of semi-static exposure methods with fish can reduce the logistical issues of waste water disposal and facilitate aspects of animal husbandry relevant to MMNs. There are concerns that the existing bioaccumulation tests are conceptually flawed for MNMs and that new test(s) are required. In vitro testing strategies, as exemplified by genotoxicity assays, can be modified for MNMs, but the risk of false negatives in some assays is highlighted. In conclusion, most protocols will require some modifications and recommendations are made to aid the researcher at the bench.

Macroscopic Wall Number Analysis of Single-Walled, Double-Walled, and Few-Walled Carbon Nanotubes by X-ray Diffraction

The layer number is of great importance for nanocarbon materials, such as carbon nanotubes (CNTs) and graphene. While simple optical methods exist to evaluate few-layer graphene, equivalent analysis for CNTs is limited to transmission electron microscopy. We present a simple macroscopic method based on the (002) X-ray diffraction peak to evaluate the average wall number of CNTs in the range from single- to few-walled. The key was the finding that the (002) peak could be decomposed into two basic components: the intertube structure (outer-wall contacts) and the intratube structure (concentric shells). Decomposition of the peaks revealed a linear relationship between the average wall number and the ratio of the intertube and intratube contributions to the (002) peak. Good agreement with CNTs having average wall numbers ranging from 1 to ∼5 demonstrated this as a macroscopic method for average wall number analysis.

Optical determination of the flexural rigidity of carbon nanotube ensembles

We demonstrate two simple and consistent optical methods for quantitatively determining the flexural rigidity EI (where E is the elastic modulus and I the moment of inertia), a quantity of practical importance in determining the deflection and buckling characteristics of carbon nanotubes (CNTs). This is done through monitoring the deflection of patterned arrays of CNTs, which are subject to fluid flow. In addition to mechanical characterization of filamentous nanostructures, the implications of our work extend to the monitoring of nanoscale fluid flows for tactile and shear force sensors and the characterization of the mechanosensor response of cilia in physiology.

Quantitative analysis of multi‐protein interactions using FRET: Application to the SUMO pathway

Protein-protein binding and signaling pathways are important fields of biomedical science. Here we report simple optical methods for the determination of the equilibrium binding constant K(d) of protein-protein interactions as well as quantitative studies of biochemical cascades. The techniques are based on steady-state and time-resolved fluorescence resonance energy transfer (FRET) between ECFP and Venus-YFP fused to proteins of the SUMO family. Using FRET has several advantages over conventional free-solution techniques such as isothermal titration calorimetry (ITC): Concentrations are determined accurately by absorbance, highly sensitive binding signals enable the analysis of small quantities, and assays are compatible with multi-well plate format. Most importantly, our FRET-based techniques enable us to measure the effect of other molecules on the binding of two proteins of interest, which is not straightforward with other approaches. These assays provide powerful tools for the study of competitive biochemical cascades and the extent to which drug candidates modify protein interactions.

Interaction of hemoglobin and copper nanoparticles: implications in hemoglobinopathy

Here we study the interaction of copper nanoparticles (CuNPs) with different variants of hemoglobin (Hb). The study reports analysis with HbA0 (the major component of human Hb) and HbA2 (a variant that is associated with β-thalassemia). In the case of HbA0, the major fraction of human Hb, the CuNPs trigger protein aggregation, and this is followed by the precipitation of the protein. The aggregative response is largely attenuated in the case of HbA2. The difference between the two variants is thus amenable to detection by simple optical methods. We verified that CuNPs co-precipitated with specific Hb variants using atomic absorption spectroscopy (AAS) and high-pressure liquid chromatography (HPLC). An associated observation was the reversal of zeta potential of HbA0 induced by the CuNPs (from –11 mV to +13 mV). Dynamic light-scattering (DLS) studies indicated that in the case of HbA0, protein initially broke the nanoclusters into smaller sizes (4 nm), and this was followed by a gradual increase in cluster size. Assays of heme peroxidase activity indicated that the protein unfolded during the process. It is suggested that interaction between the CuNPs and HbA0 stimulates the molten-globule state of the protein, leading to the onset of such an aggregative pathway. When studied for other variants, HbE, a common mutant of Hb, showed similar aggregative behavior, and on the other hand, rare variants such as HbC tended to remain in solution. A suitable scaling up of the approach may have important implications in screening hemoglobinopathies such as β-thalassemia.

26.1: Simple and Accurate Optical Reflection and Phase Compensation Methods for Reflective LCD Cell Gap

AbstractWe developed two fast, simple, and accurate optical methods for reflective LCD cell‐gap measurements. One method uses optical reflection, while the other uses optical phase compensation. They have higher accuracy, simpler setup and procedure, and lower cost than the present optical interference method. The typical measurement accuracy is about 0.05, 0.1, and 0.3um respectively, for phase compensation, optical reflection, and optical interference methods.

Correlation between polar values and vector analysis

Purpose: To evaluate the possible correlation between polar value and vector analysis assessment of surgically induced astigmatism.Setting: Department of Ophthalmology, Aalborg Sygehus Syd, Denmark.Methods: The correlation between polar values and vector analysis was evaluated by simple mathematical and optical methods using accepted principles of trigonometry and first-order optics.Results: Vector analysis and polar values report different aspects of surgically induced astigmatism. Vector analysis describes the total astigmatic change, characterized by both astigmatic magnitude and direction, while the polar value method produces a single, reduced figure that reports flattening or steepening in preselected directions, usually the plane of the surgical meridian. There is a simple Pythagorean correlation between vector analysis and two polar values separated by an arch of 45 degrees.Conclusion: The polar value calculated in the surgical meridian indicates the power or the efficacy of the surgical procedure. The polar value calculated in a plane inclined 45 degrees to the surgical meridian indicates the degree of cylinder rotation induced by surgery. These two polar values can be used to obtain other relevant data such as magnitude, direction, and sphere of an induced cylinder. Consistent use of these methods will enable surgeons to control and in many cases reduce preoperative astigmatism.

Review of surface pretreatments for aluminium alloys

The pretreatment of aluminium to enhance adhesion has been the subject of a very large amount of research. In this review, 41 mechanical, chemical, electro chemical or other treatments specifically designed to modify the surface of aluminium to enhance bond durability have been identified. These may be combined with a range of chemical “add-ons”, such as primers, coupling agents or hydration inhibitors to stabilise the surface during storage or to further enhance bond durability. Furthermore, a diverse range of surface analytical techniques have also been identified, these range from simple wettability or optical inspection methods to more complex and costly ultra high vacuum based techniques, for example, AES and XPS/ESCA. These techniques provide useful data in adhesion studies, for example, in studying surface chemistry and topography before and after treatment, or, in failure analysis. An indication is given, wherever possible, as to how the treatments perform in comparative durability trials.

Lens-on-surface method for investigating adhesion of Staphylococcus aureus to solid surfaces incubated in blood plasma.

Adhesion of Staphylococcus aureus was investigated on flat silicon oxide surfaces that had been incubated in human plasma at different concentrations. Adhesion of bacteria did not occur at high incubation concentrations of plasma or when the surface had been incubated in egg albumin. However, significant adhesion was observed when plasma was diluted. With the use of antibody method, it was noted that the adhesion of the bacteria coincided with adsorbed fibrinogen, and possibly also with IgG. We also investigated the effect of "narrow space" on the adsorption of blood plasma and subsequent adhesion of S. aureus. In these experiments, blood plasma was incubated under a convex lens placed upside-down on the silicon oxide surface. This method creates a continuous gradient of space from the contact point of the lens and outward. After rinsing off the plasma and the lens, the surface was incubated with a suspension of S. aureus followed by quantification of the attached bacteria by means of optical methods. Adhesion of bacteria occurred in several circular zones that were easily detectable with the naked eye or by the means of simple optical methods. In addition, in these experiments, adhesion coincided with adsorbed fibrinogen or IgG at the surfaces. The increased bacterial adhesion to surfaces incubated in diluted plasma, or plasma incubated in narrow space, is a variant of the so-called "Vroman effect." With a model protein system consisting of fibrinogen and IgG and the corresponding antibodies, we demonstrate that "dilution" and "incubation in narrow space" are two phenomenologically similar methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell thickness and surface pretilt angle measurements of a planar liquid-crystal cell with obliquely incident light

Two simple and fast optical methods are presented for the cell thickness and the surface pretilt angle measurements of a planar-oriented liquid-crystal (LC) cell, in which the LC director always lies in a plane of a Cartesian coordinate system. The methods employ an obliquely incident light propagating in the same plane containing the liquid-crystal molecules. Simple analytic formulas for the angular-dependent optical transmission are obtained. The phase retardation between the ordinary and extraordinary waves is used to measure the cell thickness with the use of a compensator. Independent data can be obtained for the cell thickness measurement by varying the angle of incidence of the incident light. The phase retardation-extremum method is used to measure the pretilt angle. Approximate formulas relating the pretilt angle and the angle of incidence corresponding to the transmission minimum are also obtained for the pretilt angle measurement for vertically and parallel-oriented LC cells with a small pretilt angle. For the parallel cell, the approximate formula agrees with that obtained by Birecki and Kahn [The Physics and Chemistry of Liquid Crystal Devices, edited by G. J. Sprokel (Plenum, New York, 1980), p. 115]. The methods are applicable to a planar LC cell, including the planar parallel nematic LC, homeotropic nematic LC cell, obliquely oriented nematic LC cell, and the planar-oriented ferroelectric smectic LC cell.

Plasticity of protective oxide scales

There is still some debate on the extent of plasticity of oxide scales at high temperatures. Examination of scales after creep of the substrate often shows that at higher strain rates scale cracks are visible after only very low strains (brittle behaviour), whereas at low strain rates no scale cracks are observed after large strains, at least when simple optical methods are applied. In this paper, the possible mechanisms of scale deformation are discussed with the help of deformation mechanism maps constructed for grain sizes of the order of magnitude encountered in surface oxide scales. As well as ‘genuine’ plasticity by creep of the scale, mechanisms of ‘pseudoplasticity’ are discussed. These consist of simultaneous cracking and healing processes in the scale and simulate macroscopic plasticity of the oxide. Examples from experiments are shown for through scale cracking plus rapid healing and microcracking plus healing. In model calculations critical strain rates are assessed below which the scales are macroscopically intact.MST/1160