Calculation of optical signal using three-dimensional bidomain/diffusion model reveals distortion of the transmembrane potential

Optical mapping experiments allow investigators to view the effects of electrical currents on the transmembrane potential, V_m, as a shock is applied to the heart. One important consideration is whether the optical signal accurately represents V_m. We have combined the bidomain equations along with the photon diffusion equation to study the excitation and emission of photons during optical mapping of cardiac tissue. Our results show that this bidomain/diffusion model predicts an optical signal that is much smaller than V_m near a stimulating electrode, a result consistent with experimental observations. Yet, this model, which incorporates the effect of lateral averaging, also reveals an optical signal that overestimates V_m at distances >1 mm away from the electrode. Although V_m falls off with distance r from the electrode as exp(−r/λ)/r, the optical signal decays as a simple exponential, exp(−r/λ). Moreover, regions of hyperpolarization adjacent to a cathode are emphasized in the optical signal compared to the region of depolarization under the cathode. Imaging methods utilizing optical mapping techniques will need to account for these distortions to accurately reconstruct V_m.     

The Role of Photon Scattering in Voltage-Calcium Fluorescent Recordings of Ventricular Fibrillation

Recent optical mapping studies of cardiac tissue suggest that membrane voltage (V_m) and intracellular calcium concentrations (Ca) become dissociated during ventricular fibrillation (VF), generating a proarrhythmic substrate. However, experimental methods used in these studies may accentuate measured dissociation due to differences in fluorescent emission wavelengths of optical voltage/calcium (V_opt/Ca_opt) signals. Here, we simulate dual voltage-calcium optical mapping experiments using a monodomain-Luo-Rudy ventricular-tissue model coupled to a photon-diffusion model. Dissociation of both electrical, V_m/Ca, and optical, V_opt/Ca_opt, signals is quantified by calculating mutual information (MI) for VF and rapid pacing protocols. We find that photon scattering decreases MI of V_opt/Ca_opt signals by 23% compared to unscattered V_m/Ca signals during VF. Scattering effects are amplified by increasing wavelength separation between fluorescent voltage/calcium signals and respective measurement-location misalignment. In contrast, photon scattering does not affect MI during rapid pacing, but high calcium dye affinity can decrease MI by attenuating alternans in Ca_opt but not in V_opt. We conclude that some dissociation exists between voltage and calcium at the cellular level during VF, but MI differences are amplified by current optical mapping methods.     

Combining Voltage and Calcium Imaging from Neuronal Dendrites

The ability to monitor membrane potential (V _m) and calcium (Ca²⁺) transients at multiple locations on the same neuron can facilitate further progress in our understanding of neuronal function. Here we describe a method to combine V _m and Ca²⁺ imaging using styryl voltage sensitive dyes and Fura type UV-excitable Ca²⁺ indicators. In all cases V _m optical signals are linear with membrane potential changes, but the calibration of optical signals on an absolute scale is presently possible only in some neurons. The interpretation of Ca²⁺ optical signals depends on the indicator Ca²⁺ buffering capacity relative to the cell endogenous buffering capacity. In hippocampal CA1 pyramidal neurons, loaded with JPW-3028 and 300 μM Bis-Fura-2, V _m optical signals cannot be calibrated and the physiological Ca²⁺ dynamics are compromised by the presence of the indicator. Nevertheless, at each individual site, relative changes in V _m and Ca²⁺ fluorescence signals under different conditions can provide meaningful new information on local dendritic integration. In cerebellar Purkinje neurons, loaded with JPW-1114 and 1 mM Fura-FF, V _m optical signals can be calibrated in terms of mV and Ca²⁺ optical signals quantitatively reveal the physiological changes in free Ca²⁺. Using these two examples, the method is explained in detail.     

Optical and dielectric response of two-dimensional WX2 (X = Cl,O, S,Se, Te) monolayers: A comprehensive study based on density functional theory

Here, we study the dielectric and optical properties of two-dimensional (2D) WX₂ monolayers, where X is Cl, O, S, Se, and Te. First principle electronic band structure calculations reveal that all materials are direct band gap semiconductors except WO₂ and WCl₂, which are found to be indirect band gap semiconducting 2D materials. The dielectric response of these materials is also systematically investigated. The obtained results suggest that these materials are suitable as dielectric materials to suppress unwanted signal noise. The optical properties of these 2D materials, such as absorption, reflection and extinction coefficients, refractive index, and optical conductivity, are also calculated from the dielectric function. It is found that these materials exhibit excellent optical response. The present electronic, dielectric, and optical findings indicate that WX₂ monolayers have an opportunity in electronic, optical, and optoelectronic device applications.     

Emission analysis of RE3+ (RE = Sm,Dy):B2O3‐TeO2‐Li2O‐AlF3 glasses

This article reports on the optical properties of 0.5% mol of Sm³⁺, Dy³⁺ ion‐doped B₂O₃‐TeO₂‐Li₂O‐AlF₃ (LiAlFBT) glasses. The glass samples were characterized by optical absorption and emission spectra. Judd‐Ofelt theory was applied to analyze the optical absorption spectra and calculate the intensity parameters and radiative properties of the emission transitions. The emission spectra of Sm³⁺ and Dy³⁺:LiAlFBT glasses showed a bright reddish‐orange emission at 598 nm (⁴G_5/2 → ⁶H_7/2) and an intense yellow emission at 574 nm (⁴F_9/2 → ⁶H_13/2), respectively. Full width at half maximum (FWHM), stimulated emission cross section, gain bandwidth and optical gain values were also calculated to extend the applications of the Sm³⁺ and Dy³⁺:LiAlFBT glasses. Copyright © 2012 John Wiley & Sons, Ltd.     

Nonlinear Dependences of Optical Properties of Spherical Core–Shell Silver–Gold and Gold–Silver Nanoparticles on Their Parameters

Modeling of nonlinear optical properties of spherical core–shell gold–silver and silver–gold nanoparticles (NPs) placed in water was carried out on the base of extended Mie theory. Efficiency cross sections of absorption σ _abs, scattering σ _sca, and extinction σ _ext of radiation with wavelengths λ?=?400 and 532 nm for core–shell NPs with constant core radii r ₀₀?=?5, 10, 20, and 40 nm and in the range of relative radii r ₁/r ₀₀?=?1–8 were calculated (r ₁ is the radius of shell). Dependences of optical properties of gold–silver and silver–gold NPs on increasing of core radius r ₀ in the range 0???r ₁ under condition r ₁?=?const and increasing of r ₀ under r ₁???r ₀?=?const were investigated. Results show the nonlinear behavior of optical properties of core–shell gold–silver and silver–gold NPs on radiation wavelengths (optical indexes of metals), different core and shell radii, and their correlation, on relative NP radii r ₁/r ₀₀. An increase and decrease of absorption, scattering, and extinction efficiency cross sections of core–shell NPs with changing of wavelengths, core and shell radii, and relative NP radii r ₁/r ₀₀ are established. These dependences can be used for experimental investigation of the interesting first stages of shell formation on core and optical determination of core–shell NP parameters.     

Osservazioni sulla Determinazione delle Ossidoreduttasi Piridiniche nelle Piante (Nota III)

Abstract

Remarks on determination of pyridine nucleotides-linked oxido-reductases in plants. — The optical density at 340 mμ NADH₂ or NADPH₂ suddenly decreases when NADH₂ or NADPH₂ is added to acetone precipitates of plant extracts.

This initial decrease varies according with the plant, the part used, the quantity of the precipitate and is always less than that which takes place with the corresponding extract.

The decrease in optical density-usually considered as a dehydrogenation of NADH₂ or NADPH₂ — does not seem in relation with oxigen uptake.

Indeed, when NADH₂ or NADPH₂ is added to an acetone precipitate in Warburg vessel there is a sudden change in pressure but the same happens when only water or buffer is added.

Without discussing, for the moment, the nature of this decrease in the optical density, we intend to emphasize its importance on the spectrophotometric determination at 340 mμ of NAD- or NADP-linked oxidoreductases.

In order to obtain sure and convincing results it is not sufficient, from our point of view, to consider only the changes in optical density at 340 mμ after the raction is started, but it is necessary to discuss each of them in the light of the phenomenon now reported.     

Inorganic tripton in the Finger Lakes of New York: importance to optical characteristics

Inorganic particles in the upper waters of the 11 Finger Lakes of New York are morphometrically and elementally characterized by individual particle analysis conducted with scanning electron microscopy interfaced with automated image and X-ray analyses (IPA/SAX). Coupled measurements of Secchi disk transparency (SD), the attenuation coefficient for downwelling irradiance (K_d), the beam attenuation coefficient at 660 nm, and turbidity (T_n) were made to support evaluation of the importance of non-living, inorganic particles (inorganic tripton) in regulating these optical features of water quality. Wide differences in levels of inorganic tripton, represented in terms of particle projected area per unit volume (PAV_in), and the optical measures are reported for these lakes. However, generally similar size distributions are observed for the inorganic tripton for the lakes. Terrigenous suspensoids, in the form of clay minerals, dominated the inorganic tripton particle assemblage of nine lakes, while CaCO₃, formed autochthonously, dominated in the other two and was a noteworthy contributor in four others. PAV_in is demonstrated to be an important regulator of the optical properties of these lakes, performing substantially better than chlorophyll in predicting SD, and T_n, and interlake differences in these optical measures.Contribution No. 226 of the Upstate Freshwater Institute     

Computational study of the electronic structures, UV-Vis spectra and static second-order nonlinear optical susceptibilities of macrocyclic thiophene derivatives

Using thiophene (which has a moderate resonance energy) as a spacer rather than benzene permits better π-electron delocalization and leads to a large nonlinear optical response. Thus, the nonlinear optical coefficients of a series of macrocyclic thiophene derivatives (C[3T_DA] _n with C _n symmetry) were studied, and their electronic structures, UV-Vis spectra and static second-order nonlinear optical susceptibilities (β ₀) were computed. The calculated results showed that ΔE _H-L increased and the UV-Vis spectrum redshifted as the number of C[3T_DA] units increased (one C[3T_DA] unit consists of trithiophene and diacetylene). The value of β ₀ calculated by either the ZINDO-SOS or the FF method showed the same trend: the absolute value of β ₀ increased as the number of units increased. The value of β ₀ predicted by ZINDO-SOS was an order of magnitude larger than that predicted by the FF method. However, the results suggest that macrocyclic thiophene compounds potentially exhibit large static second-order nonlinear optical susceptibilities.     

Surface Plasmon Resonance Enhanced Faraday Rotation in Fe3O4/Ag Nanoparticles Doped Diamagnetic Glass

Diamagnetic TeO₂-PbO-B₂O₃ glasses were melt-quenching fabricated and characterized for Fe₃O₄/Ag nanoparticles doping through radio-frequency sputtering and thermal treatment techniques. The surface plasmon resonance influenced structure, composition, optical, and magneto optical properties of Fe₃O₄/Ag doped glasses were investigated through XRD, SEM, XPS analysis, and Faraday rotation measurement. The optimized sputtering and thermal conditions Fe₃O₄ and Ag nanoparticles were obtained. Under the optimized conditions, a great enhancement of Faraday rotation, thermal property, and big UV cutoff red-shift due to the excited surface plasma’s resonance effect was achieved in diamagnetic glass.

     

The effect of ethoxyzolamide, an analogue of insect juvenile hormone, nor-adrenaline and iodine on changes in the optical path difference in the excretory cells and oesophagus during exsheathment in Haemonchus contortus

Davey K. G., Sommerville R. I. and Rogers W. P. 1982. The effect of ethoxyzolamide, an analogue of insect juvenile hormone, nor-adrenaline and iodine on changes in the optical path difference in the excretory cells and oesophagus during exsheathment in Haemonchus contortus. International Journal for Parasitology12: 509–513. Ethoxyzolamide, an inhibitor of carbonic anhydrase, markedly inhibits exsheathment of Haemonchus when the larvae are subsequently exposed to an exsheathing stimulus of CO₂ at 38.5°C. Ethoxyzolamide at 2 × 10^?5M does not prevent the increase in optical path difference in the oesophageal region which normally accompanies exsheathment, but markedly inhibits the increase in optical path difference in the excretory cells. An analogue of juvenile hormone (JHA; the methyl ester of 3,7,11 trimethyl-7,11-dichloro-2-dodecenic acid) does not affect the optical path difference in either the oesophagus or the excretory cells of ensheathed worms. When worms are artificially desheathed by exposure to NaOCl, a procedure which mimics the effect of CO₂ upon the oesophagus, but which does not affect the excretory cells, subsequent exposure to JHA at room temperature increases the optical path difference in the excretory cells. This increase is enhanced by subsequent incubation of the worms at 38.5°C at 30–60 min and further enhanced when CO₂ is present during the incubation at 38.5°C. The stimulation of the excretory cells by JHA is inhibited by ethoxyzolamide at 2 × 10^?5M. Noradrenaline at 10^?3M has no effect on ensheathed larvae, but causes an increase in optical path difference in the excretory cells of larvae desheathed with NaOCl. This increase is inhibited by ethoxyzolamide. A brief exposure to I₂ blocks the response of the excretory cells of both CO₂ and JHA, but does not significantly reduce the effect of nor-adrenaline. On the basis of these and previous results, it is proposed that both CO₂ and JHA stimulate a hypothetical CO₂ receptor which leads to the release of nor-adrenaline. The noradrenaline in turn stimulates, either directly or indirectly, the excretory cells.     

A new approach in the design of polar crystals for quadratic nonlinear optics exemplified by the synthesis and crystal structure of 2-amino-5-nitropyridinium dihydrogen monophosphate (2A5NPDP)

2-amino-5-nitropyridinium dihydrogen monophosphate exemplifies a new crystal engineering strategy combining mineral and organic moieties towards enhanced quadratic nonlinear optical properties. This strategy is meant to combine the advantages of mineral ionic structures (cohesion, stability, optical and other damage resistance) with those of organic molecules (structural flexibility, high optical polarizability). This organic inorganic material is designed so as to favour mutual dipolar interactions between the 2-amino-5-nitropyridinium cations and the (H₂PO ₄ ^– ) _n subnetwork interlocked by hydrogen bonding in the same crystalline lattice. This approach rests on the structural features and chemical properties of (H₂PO ₄ ^– ) _n polyanion. The 2A5NPDP structure reveals a polar layered arrangement. The high powder SHG efficiency of 2A5NPDP, comparable to that of state-of-the-art purely organic 3-methyl-4-nitropyridine-1-oxide (POM) crystals, confirms the validity of this approach, currently generalized to a large variety of mixed organo-mineral crystals.     

Luminescent inorganic mixed borate phosphors materials for lighting

The need of new materials with desirable optical properties has become important in recent years. In particular, a need has emerged for compounds having better luminescence properties in various practical applications. The introduction of rare earth ions as activators improves the luminescence properties of the compounds considerably. Boron is one of the most abundant elements in nature. It readily combines with almost all other elements. In combination with oxygen; it forms borates comprised of various anions such as BO₃³⁻, B₂O₅⁴⁻, etc. Apart from these simple borates, several complex compositions exist involving mixed anions as well as double metal borates, due to the three-fold, or four-fold coordination of borate atoms. Borates intrinsically possesses characteristics that are advantageous for optical materials, which include a wide transparency range, large electronic band gap, good thermal and chemical stability, low preparative temperature, optical stability with good nonlinear characteristics, and an exceptionally high optical damage threshold. The unique crystal structure of borates determines their enhanced ultraviolet light transparency, good nonlinearity, and relatively high resistance against laser-induced damage. Some of these complex borates have interesting luminescence properties that are covered in this review. These include double borates containing rare earths RM₃(BO₃)₄, pentaborates LaMgB₅O₁₀, M₃R₂(BO₃)₄, where M is an alkaline earth, mixed anion borates such as aluminoborate SrAl₂B₂O₇, silicate-borates such as pekovite, SrB₂Si₂O₈, haloborates, M₂B₅O₉X, where M is an alkaline earth and X is a halogen, phosphate borates, and MBPO₅, where M is an alkaline earth. Phosphors based on these compositions find use in various applications such as fluorescence lamps, colour TVs, plasma display panels, high-intensity discharge lamps based on xenon, optically pumped solid-state lasers, eye-safe lasers, and X-ray imaging.     

Optical and NMR dose response of N-isopropylacrylamide normoxic polymer gel for radiation therapy dosimetry

Background

Application of less toxic normoxic polymer gel of N-isopropyl acrylamide (NIPAM) for radiation therapy has been studied in recent years.

Aim

In the current study the optical and NMR properties of NIPAM were studied for radiation therapy dosimetry application.

Materials and methods

NIPAM normoxic polymer gel was prepared and irradiated by 9 MV photon beam of a medical linac. The optical absorbance was measured using a conventional laboratory spectrophotometer in different wavelengths ranging from 390 to 860 nm. R₂ measurements of NIPAM gels were performed using a 1.5 T scanner and R₂–dose curve was obtained.

Results

Our results showed R₂ dose sensitivity of 0.193 ± 0.01 s⁻¹ Gy⁻¹ for NIPAM gel. Both R₂ and optical absorbance showed a linear relationship with dose from 1.5 to 11 Gy for NIPAM gel dosimeter. Moreover, absorbance–dose response varied considerably with light wavelength and highest sensitivity was seen for the blue part of the spectrum.

Conclusion

Our results showed that both optical and NMR approaches have acceptable sensitivity and accuracy for dose determination with NIPAM gel. However, for optical reading of the gel, utilization of an optimum optical wavelength is recommended.     

Over 104-fold amplified upconversion luminescence of lanthanide nanocrystals through optical oscillator-like system

Recently, lanthanide (Ln) luminescent nanocrystals have attracted increasing attention in various fields such as biomedical imaging, lasers, and anticounterfeiting. However, due to the forbidden 4f–4f transition of lanthanide ions, the absorption cross-section and luminescence brightness of lanthanide nanocrystals are limited. To address the challenge, we constructed an optical oscillator-like system to repeatedly simulate lanthanide nanocrystals to enhance the absorption efficiency of lanthanide ions on excitation photons. In this optical system, the upconversion luminescence (UCL) of Tm³⁺ emission of ~450 nm excited by a 980 nm laser can be amplified by a factor beyond 10⁴. The corresponding downshifting luminescence of Tm³⁺ at 1460 nm was enhanced by three orders of magnitude. We also demonstrated that the significant luminescence enhancement in the designed optical oscillator-like system was general for various lanthanide nanocrystals including NaYF₄:Yb³⁺/Ln³⁺, NaErF₄@NaYF₄ and NaYF₄:Yb³⁺/Ln³⁺@NaYF₄:Yb³⁺@NaYF₄ (Ln = Er, Tm, Ho) regardless of the wavelengths of excitation sources (808 and 980 nm). The mechanism study revealed that both elevated laser power in the optical system and multiple excitations on lanthanide nanocrystals were the main reason for the luminescence amplification. Our findings may benefit the future development of low-threshold upconversion and downshifting luminescence of lanthanide nanocrystals and expand their applications.     

Study of Design Tunable Optical Sensor and Monochromatic Filter of the One-Dimensional Periodic Structure of TiO2/MgF2 with Defect Layer of Liquid Crystal (LC) Sandwiched with Two Silver Layers

In this paper, we have inspected the optical characteristics of one-dimensional periodic structure (1DPS) of TiO₂ and MgF₂ dielectric materials with defect layer of liquid crystal (LC) sandwiched with two silver layers, i.e., (TiO₂|MgF₂)³|Ag|LC|Ag|(TiO₂/MgF₂)³ using transfer matrix method (TMM). The optical tunable properties of considered periodic structures investigated at different incident angles and temperatures for TE and TM modes. Our study shows that absorption peak of 1DPS varies with incident angle and temperature. The defect layer (Ag-LC-Ag), sandwiched LC within two metallic (Ag) layers, exhibits the surface plasmon waves at the metal LC interfaces. The effect of surface plasmon waves can be better understand through the optical sensing property of such defect periodic structure. The detailed study concludes that such a type of one-dimensional periodic structure (1DPS) may be useful to design a tunable sensor and monochromatic filter.

     

Study of optical properties of electropolymerized melanin films by photopyroelectric spectroscopy

Photopyroelectric (PPE) spectroscopy, in the 350–1,075 nm wavelength range, was used to study the optical properties of electropolymerized melanin films on indium tin oxide (ITO) coated glass. The PPE intensity signal as a function of the wavelength λ, V _n(λ) and its phase F _n(λ) were independently measured. Using the PPE signal intensity and the thermal and optical properties of the pyroelectric detector, we were able to calculate the optical absorption coefficient β of melanin in the solid-state. We believe this to be the first such measurement of its kind on this material. Additionally, we found an optical gap in these melanin films at 1.70 eV.     

Effects of Nanoparticle Shape and Size on Optical Properties of LaB<Subscript>6</Subscript>

The optical response of lanthanum hexaboride (LaB₆) nanoparticles has been investigated by both theoretically and experimentally. The LaB₆ nanoparticles obtained by solid-state reaction could avoid serious surface oxidization and exhibit excellent optical performance. The discrete dipole approximation (DDA) has been used to investigate the optical response of LaB₆ nanoparticles with different sizes and different shapes. The calculation results coincide with the experimental results and reveal that the largest extinction peak value appears at 60 nm for cubic particles and 40 nm for spherical particles, respectively. Our calculation results show that the existence of the largest extinction peak value is not only due to the surface oxides but also relate to the particle shape of LaB₆ compound. In addition, the LaB₆ nanoparticles with cubic and spherical shapes exhibit different optical responses, and the cubic particles exhibit stronger near infrared (NIR) extinction than spherical particles. With increasing particle size, the extinction peak value of spherical particle decreases more rapidly than that of cubic ones.     

Development of Bioluminescent Bioreporters for In Vitro and In Vivo Tracking of Yersinia pestis

Yersinia pestis causes an acute infection known as the plague. Conventional techniques to enumerate Y. pestis can be labor intensive and do not lend themselves to high throughput assays. In contrast, bioluminescent bioreporters produce light that can be detected using plate readers or optical imaging platforms to monitor bacterial populations as a function of luminescence. Here, we describe the development of two Y. pestis chromosomal-based luxCDABE bioreporters, Lux_PtolC and Lux_PcysZK. These bioreporters use constitutive promoters to drive expression of luxCDABE that allow for sensitive detection of bacteria via bioluminescence in vitro. Importantly, both bioreporters demonstrate a direct correlation between bacterial numbers and bioluminescence, which allows for bioluminescence to be used to compare bacterial numbers. We demonstrate the use of these bioreporters to test antimicrobial inhibitors (Lux_PtolC) and monitor intracellular survival (Lux_PtolC and Lux_PcysZK) in vitro. Furthermore, we show that Y. pestis infection of the mouse model can be monitored using whole animal optical imaging in real time. Using optical imaging, we observed Y. pestis dissemination and differentiated between virulence phenotypes in live animals via bioluminescence. Finally, we demonstrate that whole animal optical imaging can identify unexpected colonization patterns in mutant-infected animals.     

A comprehensive study on the electronic structure,dielectric and optical properties of alkali-earth metals and transition metal hydroxides M(OH)2

In the present work, the physical properties of alkali-earth metal and transition metal hydroxides are comprehensively investigated using the density functional theory. Here, the alkali-earth metals Ca, Mg, and transition metals Cd, Zn are considered from the II-A and II-B groups in the periodic table of elements. The first principle electronic structure calculations show that these bulk hydroxide materials are direct band gap material. Ca(OH)₂ and Mg(OH)₂ exhibit an insulating behavior with a very large band gap. However, Cd(OH)₂ and Zn(OH)₂ are found to be wide band gap semiconductors. The dielectric and optical studies reveal that these materials have a high degree of anisotropy. Hence, the light propagation in these materials behaves differently in the direction perpendicular and parallel to the optical axis, and exhibits birefringence. Therefore, these materials may be useful for optical communication. The calculated electron energy loss suggests that these materials can also be used for unwanted signal noise suppression. The wide band gap makes them useful for high-power applications. Moreover, Ca(OH)₂ and Mg(OH)₂ are found to be suitable for dielectric medium.