Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators ^1,2. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials.Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides ³, asymmetric split-ring resonators ⁴, and photonic band gap structures integrated into parallel-plate waveguides ⁵. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc.The sensor design we use here is based on a simple parallel-plate waveguide ^6,7. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE₁) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove ^6,8. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index ⁹.Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves ¹⁰. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.     

Integrated Terahertz Surface Plasmon Resonance on Polyvinylidene Fluoride Layer for the Profiling of Fluid Reflectance Spectra

We design terahertz (THz) surface-plasmon-resonance (SPR) sensors using a ferroelectric polyvinylidene fluoride (PVDF) thin layer for biological sensing. The reflectivity properties based on SPR are described using transfer matrix method (TMM) and numerically simulated using finite-difference time domain (FDTD) method. The sensing characteristics of the structure are systematically analyzed through the examination of the reflectivity spectrum. The results reveal that the pronounced SPR resonance peak has quasi-linear relationship with the refractive index variation of the material under investigation. Through analyzing and optimizing the structural parameters of the THz SPR sensor, we achieved the theoretical value of the refractive index detection sensitivity as high as 0.393 THz/unit change of refractive index (RIU) for a 20-μm-thick liquid sample with a 10-μm PVDF layer. This work shows great promise toward realizing a THz SPR sensor with high sensitivity for identifying the signatures of biological fluid sample.     

Strain Field Mapping of Dislocations in a Ge/Si Heterostructure

Ge/Si heterostructure with fully strain-relaxed Ge film was grown on a Si (001) substrate by using a two-step process by ultra-high vacuum chemical vapor deposition. The dislocations in the Ge/Si heterostructure were experimentally investigated by high-resolution transmission electron microscopy (HRTEM). The dislocations at the Ge/Si interface were identified to be 90° full-edge dislocations, which are the most efficient way for obtaining a fully relaxed Ge film. The only defect found in the Ge epitaxial film was a 60° dislocation. The nanoscale strain field of the dislocations was mapped by geometric phase analysis technique from the HRTEM image. The strain field around the edge component of the 60° dislocation core was compared with those of the Peierls–Nabarro and Foreman dislocation models. Comparison results show that the Foreman model with a = 1.5 can describe appropriately the strain field around the edge component of a 60° dislocation core in a relaxed Ge film on a Si substrate.     

Tamm Plasmon Polariton as Refractive Index Sensor Excited by Gyroid Metals/Porous Ta2O5 Photonic Crystal

In this paper, a novel refractive index sensor in terahertz region is proposed. The proposed structure is prism/(sample/porousTa₂O₅)¹⁵/sample/gyroid metal/substrate. The sensor is based on the Tamm plasmon polariton at the interface between porous one-dimensional photonic crystal and gyroidal metal. The gyroidal metal has been used as an alternative metal and its refraction index can be tuned by the gyroid parameters. The effects of the metal volume fraction and sample refractive index on the performance are studied to improve the ability of the sensor. The proposed sensor achieves high sensitivity of 6.7 THz/RIU, a high figure of merit 6*10³ RIU^?1, a high-quality factor of 3*10³, and a low detection limit of 9*10^?6 RIU. The proposed device can be a good candidate for fabricating gyroid metal and porous material-based biosensors, active optoelectronic and polaritonic devices.

     

High frequency antigens of human erythrocyte membrane sialoglycoproteins, V. Characterization of the Gerbich blood group antigens: Ge2 and Ge3

The molecular properties of the major, high-frequency antigens (Ge2 and Ge3) of the human Gerbich blood group system were investigated using 14 different alloantibodies from rare Ge: -1,-2,-3 or Ge: -1,-2,3 individuals. Various modification, fractionation or fragmentation products of glycophorins (sialoglycoproteins) from normal erythrocytes (phenotype Ge: 1,2,3) were used in hemagglutination inhibition assays. The location of the antigens was also studied by blotting of proteins, separated by dodecyl sulfate polyacrylamide gel electrophoresis, to nitrocellulose and detection of bound antibodies by 125I-labelled protein G. Anti-Ge3 was found to be directed against a region of glycophorin C that surrounds a tryptic cleavage site at position 48 and a similar region of glycophorin D whose structure is not yet known. NeuAc residue(s), probably representing part(s) of a carbohydrate unit attached to serine42 of glycophorin C, methionine, aspartic or glutamic acid, tryptophan and/or arginine residue(s) are involved in the Ge3 epitopes, as judged from chemical modification. The Ge2 epitopes were found to be located on a tryptic glycopeptide from glycophorin D comprising about 20-30 amino-acid residues. NeuAc residue(s), attached to serine-/threonine-linked oligosaccharide(s), are involved in the Ge2 determinants. Using the immunoblotting technique, it could also be shown that the 'new' glycophorin in Ge: -1,-2,3 cells carries the Ge3 antigen.     

Effects of Germanium (Ge) on the silica spicules of the marine sponge Suberites domuncula: Transformation of spicule type

Germanium (Ge), in the form of germanic acid, at a Ge/Si molar ratio of 1.0 inhibits gemmule development and silica deposition in the marine demosponge Suberites domuncula. Lower Ge/Si ratios inhibit the growth in length of the silica spicules (tylostyles) producing short structures, but with relatively normal morphology and close to normal width; spherical protuberances occasionally occur on these spicules. A few of the short spicules possess completely round rather than pointed tips. Many of the latter develop when Ge is added (pulsed) to growing animals, thus inducing a change in spicule type. These results indicate that the growth in length of the axial filament is more sensitive to Ge inhibition than is silica deposition and that pointed spicule tips normally develop because the growth of the axial filament at the spicule tip is more rapid than silica deposition. Newly formed spicules initiate silica deposition at the spicule head but the absence of Ge-induced bulbs as in freshwater spicules (oxeas) leaves open the question of whether there is a silicification center(s) present in Suberites tylostyles. The morphogenesis of freshwater oxeas and of marine tyolstyles appears fundamentally different-bidirectional growth in the former and unidirectional growth in the latter. X-ray analysis demonstrate relatively uniform Ge incorporation into the silica spicules with considerable variation from spicule to spicule in the incorporated level. Increased silicic acid concentration induces the formation of siliceous spheres, suggesting that the axial filament becomes prematurely encased in silica.     

Tunable Terahertz Filters Based on Graphene Plasmonic All-Dielectric Metasurfaces

A tunable terahertz filter based on graphene plasmonic all-dielectric metasurfaces is proposed and investigated numerically by using the finite-difference time-domain (FDTD) method. Especially, hybrid all-dielectric metasurfaces are used to make a whole single-sheet graphene forms two different conductivity patterns with the same gate voltage. The simulated results show that resonance wavelength is shifted significantly with the change of gate voltage. Besides, the transmittance spectra are also shifted with the change of the width of SiC, and the filter shows a polarization-dependent modulation property for the length and the width of SiC being 480 and 320 nm, respectively. In addition, the filter can be applied for refractive sensing because the transmittance spectra are shifted with the change of the background refractive index. The study could provide availability for versatile tunable terahertz graphene plasmonic metasurfaces.     

Refractive index and thickness of the outer layer of particles of dispersed perfluorochemical-based blood substitutes

A calculation of the refractive index of particles of a disperse perfluorochemical-based (PFC-based) blood substitute has been made taking into account particular features of the structure of PFC emulsion particles and the equations earlier obtained by one of the authors in the studies on light interaction with optically inhomogeneous 2- and 3-layer spheres. The possibility of averaging by volume the refractive index of 2-layer emulsion particles has been shown. The refractive index of PFC particles has been experimentally determined using independent optical methods, and the thickness of the particle shell formed by a surfactant has been evaluated.     

Ultrafast Nano-scale Optical Switching in a Plasmonic Interferometer with Enhanced Tunability

An all-optical switch based on plasmonic metal–insulator–metal (MIM) waveguides and the Mach–Zehnder (MZ) interferometer is designed. In order to realize an all-optical and active switch, a nonlinear material with intensity-dependent refractive index is introduced in one arm. Other than studying a typical MZ structure, we also investigate the asymmetric case where unequal thicknesses and distances for MZ arms are proposed. The finite element method (FEM) with a refined triangle mesh is employed for simulations. Results for ON and OFF states are provided with or without employing the pump field. Investigation of the geometrical dispersion reveals tunability of the structure for specific frequencies in the terahertz region. Finally, we show that introducing asymmetric arms provides better tunability in the designed ultrafast nano-scale switch and suggests its potential applications in integrated optical circuits.

     

Utilizing the Metallic Nano-Rods in Hexagonal Configuration to Enhance Sensitivity of the Plasmonic Racetrack Resonator in Sensing Application

A high sensitive plasmonic refractive index sensor based on metal-insulator-metal (MIM) waveguides with embedding metallic nano-rods in racetrack resonator has been proposed. The refractive index changes of the dielectric material inside the resonator together with temperature changes can be acquired from the detection of the resonance wavelength, based on their linear relationship. With optimum design and considering a tradeoff among detected power, structure size, and sensitivity, the finite difference time domain simulations show that the refractive index and temperature sensitivity values can be obtained as high as 2610 nm per refractive index unit (RIU) and 1.03 nm/°C, respectively. In addition, resonance wavelengths of resonator are obtained experimentally by using the resonant conditions. The effects of nano-rods radius and refractive index of racetrack resonator are studied on the sensing spectra, as well. The proposed structure with such high sensitivity will be useful in optical communications that can provide a new possibility for designing compact and high-performance plasmonic devices.     

Natural weathering of rape straw flour (RSF)/HDPE and nano-SiO2/RSF/HDPE composites

The use of wood polymer composites (WPCs) in industries has been growing, and this is fueled in part by the use of WPCs in the construction industry. Rape straw flour (RSF)/high-density polyethylene (HDPE) composites as WPCs can also be applied in the construction industry. As a result, the durability of RSF/HDPE composites after natural exposure becomes a concern. Fourier transform infrared (FTIR) spectroscopy is used to monitor the development of degradation products, such as carbonyl groups and vinyl groups, and to determine changes in HDPE crystallinity. Differential scanning calorimetry (DSC) is also used to analyze changes in HDPE crystallinity. The results indicate that the carbonyl index was roughly lower for the RSF/HDPE composites than for the nano-SiO₂/RSF/HDPE composites, and the concentration of vinyl groups was generally much larger for the RSF/HDPE composites than for the nano-SiO₂/RSF/HDPE composites. At the same time, carbonyl index and vinyl index decrease with an increasing depth of composites, particularly decreasing strongly from 100 to 200 μm. The crystallinity of the samples increase because of natural aging, and the values of crystallinity derived by DSC are smaller than those derived by FTIR.     

Light scattering turbidity changes as a measure of the kinetics of Ca2+-promoted aggregation of chromaffin granule membrane ghosts

Changes in turbidity seen when chromaffin granule membrane ghosts are aggregated by Ca²⁺ can be modelled as dimerization of hollow spheres using Rayleigh-Gans-Debye light-scattering theory. The experimental changes agree well with the calculations. Thus, if shape or refractive index changes produced by osmotic perturbation, ion uptake, etc. can be excluded, turbidity readings can be used to follow the progress of the aggregation reaction of storage vesicles and other small particles or macromolecules.     

Multicenter study of quantitative PET system harmonization using NIST-traceable 68Ge/68Ga cross-calibration kit

PurposeThe present study aimed to define the errors in SUV and demonstrate the feasibility of SUV harmonization among contemporary PET/CT scanners using a novel National Institute of Standards and Technology (NIST)-traceable ⁶⁸Ge/⁶⁸Ga source as the reference standard.MethodsWe used ⁶⁸Ge/⁶⁸Ga dose calibrator and PET sources made with same batch of ⁶⁸Ge/⁶⁸Ga embedded in epoxy that is traceable to the NIST standard. Bias in the amount of radioactivity and the radioactive concentrations measured by the dose calibrators and PET/CT scanners, respectively, was determined at five Japanese sites. We adjusted optimal dial setting of the dose calibrators and PET reconstruction parameters to close the actual amount of radioactivity and the radioactive concentration, respectively, of the NIST-traceable ⁶⁸Ge/⁶⁸Ga sources to harmonize SUV. Errors in SUV before and after harmonization were then calculated at each site.ResultsThe average bias in the amount of radioactivity and the radioactive concentrations measured by dose calibrator and PET scanner was −4.94% and −12.22%, respectively, before, and −0.14% and −4.81%, respectively, after harmonization. Corresponding averaged errors in SUV measured under clinical conditions were underestimated by 7.66%, but improved by −4.70% under optimal conditions.ConclusionOur proposed method using an NIST-traceable ⁶⁸Ge/⁶⁸Ga source identified bias in values obtained using dose calibrators and PET scanners, and reduced SUV variability to within 5% across different models of PET scanners at five sites. Our protocol using a standard source has considerable potential for harmonizing the SUV when contemporary PET scanners are involved in multicenter studies.     

In vivo terahertz reflection imaging of human scars during and after the healing process

We use terahertz imaging to measure four human skin scars in vivo. Clear contrast between the refractive index of the scar and surrounding tissue was observed for all of the scars, despite some being difficult to see with the naked eye. Additionally, we monitored the healing process of a hypertrophic scar. We found that the contrast in the absorption coefficient became less prominent after a few months post‐injury, but that the contrast in the refractive index was still significant even months post‐injury. Our results demonstrate the capability of terahertz imaging to quantitatively measure subtle changes in skin properties and this may be useful for improving scar treatment and management.

     

Measurements of the total solid material in the bands and interbands of the polytene chromosomes in living cells of chironomus

Summary The refractive indices of a number of bands and interbands of the polytene chromosomes in the living salivary gland cells of two species of Chironomus were measured with an interference microscope, and values were obtained for the total solid material present in each region. To make these measurements it was necessary to compress the cells until virtually no cytoplasm lay above or below the nucleus, but this produced no deleterious effects on the cells as a whole.The results indicated that there is not less than 25% of solid material in the band regions of these chromosomes, and not more than 15% of solids in the interbands. The nuclear sap of these cells was found to contain about 12% of solid material.Similar refractive index measurements were made on the bands and interbands of isolated chromosomes mounted in saline and in a 12% isotonic saline/protein solution of the same refractive index as the nuclear sap. In both these media the bands were again found to contain at least 10% more material than the interbands, but their refractive indices were lower in the saline than they were in the intact cells and markedly higher in the saline/protein. It is therefore concluded that the isolated chromosomes are, to some extent, permeable, and can permit the entry of protein molecules from the mounting medium and the egress of some or their own material.     

Computational determination of refractive index distribution in the crystalline cones of the compound eye of Antarctic krill (Euphausia superba)

In order to understand how a compound eye channels light to the retina and forms an image, one needs to know the refractive index distribution in the crystalline cones. Direct measurements of the refractive indices require sections of fresh, unfixed tissue and the use of an interference microscope, but frequently neither is available. Using the eye of the Antarctic krill Euphausia superba (the main food of baleen whales) we developed a computational method to predict a likely refractive index distribution non-invasively from sections of fixed material without the need of an interference microscope. We used a computer model of the eye and calculated the most realistic spatial distribution of the refractive index gradient in the crystalline cone that would enable the eye to produce a sharp image on the retina. The animals are known to see well and on the basis of our computations we predict that for the eyes of the adult a maximum refractive index of 1.45-1.50 in the centre of the cone yields a better angular sensitivity and light absorption in a target receptor of the retina than if N(max) were 1.55. In juveniles with a narrower spatial separation between dioptric structures and retina, however, an N(max) of 1.50-1.55 gives a superior result. Our method to determine the most likely refractive index distribution in the cone without the need of fresh material and an interference microscope could be useful in the study of other invertebrate eyes that are known to possess good resolving power, but for a variety of reasons are not suitable for or will not permit direct refractive index measurements of their dioptric tissues to be taken.     

Light scattering with stream-in-air flow systems.

Both forward angle and 90 degrees light-scattering measurements have been used for cell sizing with stream-in-air flow systems with very little theoretical base for the measurements. Mie theory calculations are compared with measurements on plastic microspheres. Detector response for homogeneous spheres is shown to be sensitive to refractive index.     

Gerbich blood group deficiency of the Ge:-1,-2,-3 and Ge:-1,-2,3 types. Immunochemical study and genomic analysis with cDNA probes

Human erythrocytes carry several transmembrane glycoproteins, among which the two minor species associated with the blood group Gerbich (Ge) antigens, GP C and GP D, play pivotal role since they interact with the membrane cytoskeleton and contribute to maintain the normal red cell shape. On the red cells from two categories of homozygous donors lacking the Ge determinants (Ge:-1,-2,-3 and Ge:-1,-2,3), GP C and GP D are missing but instead there is a new glycoprotein, easily detected by SDS/polyacrylamide gel electrophoresis, which exhibits some properties shared by GP C and GP D. This was shown by immunochemical analyses with a murine monoclonal antibody, extraction of the glycoproteins by organic solvents and binding studies with the 125I-labelled Lens culinaris lectin. The red cells from obligate heterozygotes for the Ge:-1,-2,-3 condition also carry this new glycoprotein component but in a much lesser amount than expected on the basis of one gene dose response. Using a cDNA probe containing the coding sequence of human GP C and the entire 3' untranslated region of its mRNA, we have demonstrated by Southern analyses that the Ge:-1,-2,-3 and the Ge:-1,-2,3 conditions are associated with a constant 3-kbp deletion within the GP C gene. Similar studies indicated that this gene is present as a unique copy per haploid genome of Ge-positive control donors (Ge:1,2,3). To account for these data and for the glycoprotein profile of Ge-negative erythrocytes, it is proposed that a unique Gerbich gene encodes for GP C and GP D, either by alternative RNA splicing or by different post-translational events, and that, following a 3-kbp deletion within this gene, a new glycoprotein having properties common to GP C and GP D can be produced.     

The small angle light scattering of biological cells. Theoretical considerations

The light scattered by living biological cells (assumed homogeneous spheres with a relative refractive index, m = 1.05) at small angles has been calculated by the Hodkinson approximation and the more rigorous Mie theory. Both methods predict that relative volume distributions may be estimated from low angle scattering measurements on each cell in a population. Under conditions of short wavelength illumination or strong absorption, absolute volume information may also be obtained.     

Changes in the refractive index of the stroma and its extrafibrillar matrix when the cornea swells

The transparency of the corneal stroma is critically dependent on the hydration of the tissue; if the cornea swells, light scattering increases. Although this scattering has been ascribed to the disruption caused to the arrangement of the collagen fibrils, theory predicts that light scattering could increase if there is an increased mismatch in the refractive indices of the collagen fibrils and the material between them. The purpose of this article is to use Gladstone and Dale's law of mixtures to calculate volume fractions for a number of different constituents in the stroma, and use these to show how the refractive indices of the stroma and its constituent extrafibrillar material would be expected to change as more solvent enters the tissue. Our calculations predict that solvent entering the extrafibrillar space causes a reduction in its refractive index, and hence a reduction in the overall refractive index of the bovine stroma according to the equation n'(s) = 1.335 + 0.04/(0.22 + 0.24 H'), where n'(s) is the refractive index and H' is the hydration of the swollen stroma. This expression is in reasonable agreement with our experimental measurements of refractive index versus hydration in bovine corneas. When the hydration of the stroma increases from H = 3.2 to H = 8.0, we predict that the ratio of the refractive index of the collagen fibrils to that of the material between them increases from 1.041 to 1.052. This change would be expected to make only a small contribution to the large increase in light scattering observed when the cornea swells to H = 8.