Change In Optical Transmission Research Articles

Label-free detection of DNA hybridization using gold-coated tapered fiber optic biosensors (TFOBS) in a flow cell at 1310nm and 1550nm

Abstract We had previously reported the detection of a model protein bovine serum albumin (BSA) using antibody-immobilized tapered fiber optic biosensors (TFOBS) at 1310 nm and 1550 nm under stagnant and flow conditions. Because of recent interest in pathogen detection based on DNA, in this work we explore the application of these sensors for the detection of single stranded DNA (ssDNA). We show that it is feasible to directly detect the hybridization of a 10-mer ssDNA to its complementary strand immobilized on the sensor surface. Detection was performed under flow conditions because flow reduces non-specific binding to sensor surface, eliminates optical transmission changes due to mechanical movements, and allows for instantaneous switching of samples when needed. TFOBS were fabricated with waist diameters of 5–10 μm and total lengths of 1000–1200 μm. The taper regions were coated with 50 nm of gold and housed in a specially constructed holder which served as a flow cell. The TFOBS was immobilized with 15-mer ssDNA with a C6 extension and a thiol group, which attaches to Au〈1 1 1〉 sites. Then, the complementary 10-mer ssDNA samples were allowed to flow in from low to high concentration (750 fM to 7.5 nM) and the resulting transmission changes were recorded. It is shown that 750 fM of complementary DNA can be detected. This sensor was able to distinguish between complementary DNA from DNA with a single nucleotide mismatch in the middle position.

Magnetic circular dichroism of opal crystals infiltrated with iron porphyrin

Synthetic opal crystals composed of silica spheres of diameter »250 nm were infiltrated with highly concentrated (10 mM) buffered phosphate solution of iron porphyrin (FeTPPS). Magnetic circular dichroism (MCD) in the visible spectral range was investigated on hybrid samples immersed in polar (ethanol) or non-polar (hexane, toluene) solutions and situated in magnetic field. The MCD effect was observed in the spectral region of 550–650 nm in the vicinity of Q-absorption bands of FeTPPS. In 350 mT magnetic field the relative optical transmission change by 2.4.10-4 was determined at the Q0-band of 0.3 mm thick infiltrated opal sample. The dispersion-like lineshape of MCD spectra corresponded to the A-type term. An average refraction index and refraction index contrast of composite system was controlled by immersion of infiltrated opal samples into various liquids. As a result, the spectral position of the stop band in opal photonic crystal was tuned with respect to FeTPPS absorption bands. When the Q band of FeTPPS was within the stop band of opal, the optical contrast of photonic crystal was changed by external magnetic field due to the MCD effect. Keywords: photonic band gap materials, inltrated opal, magnetooptical effects

Engineering surface plasmon based fiber-optic sensors

Ordered arrays of nanoholes with subwavelength diameters, and submicron array periodicity were fabricated on the tips of gold-coated optical fibers using focused ion beam (FIB) milling. This provided a convenient platform for evaluating extraordinary transmission of light through subwavelength apertures and allowed the implementation of nanostructures for surface plasmon engineered sensors. The fabrication procedure was straightforward and implemented on single mode and multimode optical fibers as well as etched and tapered fiber tips. Control of the periodicity and spacing of the nanoholes allowed the wavelength of operation to be tailored. Large changes in optical transmission were observed at the designed wavelengths, depending on the surrounding refractive index, allowing the devices to be used as fiber-optic sensors.

Effect of substrate temperature on structural, optical and electrical properties of spray pyrolytically grown nanocrystalline SnO2 thin films

AbstractSnO2 nanocrystalline thin films were prepared by a spray pyrolysis method on glass substrates at 375, 400, 425, 450 and 500 °C. Structural, optical and electrical properties of these films were studied by X‐ray diffraction, UV–visible and four‐probe methods. The change in electrical conductivity, band gap and optical transmittance was found to be a function of the change in lattice parameters Δa and Δc The samples prepared at 425 °C are found to have good figure of merit and maximum transmittance (96% at 550 nm). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gasochromic Properties of Nanostructured Tungsten Oxide Films Prepared by Sputtering Deposition

The effects of surface morphology on the gasochromic properties of tungsten trioxide (WO3) films are reported. WO3 films with various crystalline structures and surface morphologies are prepared by reactive rf magnetron sputtering by adjusting the substrate temperature and oxygen concentration in a sputtering gas during deposition. Grain structures on these films were confirmed by atomic force microscopy observation. The gasochromic properties of the WO3 films coated with a palladium catalyst were examined on the basis of a change in optical transmittance with 645-nm-wavelength light in 1% hydrogen in argon gas. WO3 films with a (001) orientation show sufficient gasochromic properties for their application to fiber-optic hydrogen gas sensors. The growth of the nanocrystalline structure in the WO3 films seems to improve gasochromic properties.

Tunable Optical and Swelling/Deswelling Properties Associated with Control of the Coil-to-Globule Transition of Poly(N-isopropylacrylamide) in Polymer−Clay Nanocomposite Gels

Polymer−clay nanocomposite gels (NC gels) consisting of poly(N-isopropylacrylamide) (PNIPA) and inorganic clay (hectorite) were investigated in terms of their optical and swelling/deswelling properties. Depending on the clay concentration (Cclay), NC gels exhibit unique changes in optical transmittance, optical anisotropy, and swelling/deswelling behaviors, all of which were distinct from those of chemically cross-linked hydrogels (OR gels). The optical transparency and its temperature-induced change differed greatly between NC and OR gels. The decrease in transmittance associated with the coil-to-globule transition of PNIPA occurred at higher temperatures than the normal transition temperature in NC gels as the clay concentration increased. On the assumption of the uniform and random dispersion of exfoliated clay platelets, the critical Cclay (C*clay) for spontaneous clay aggregation (layer stacking) in NC gels was calculated to be 10 × 10-2 mol/L H2O. C*clay was consistent with the experimental results,...

Evaluation of skin optical clearing enhancement with Azone as a penetration enhancer

In order to find a non-invasive way to improve the efficacy of skin optical clearing with topically applied optical clearing agents (OCA), we evaluated the effect of Azone as a chemical penetration enhancer on optical clearing of intact skin in vitro. Fresh porcine skin with topical application of glycerol (G) mixed with various concentrations of water-soluble Azone (A w) or propylene glycol (PG) mixed with oil-soluble Azone (A o) was investigated. We measured changes in optical transmittance and diffuse reflectance of the skin under treatment with a near-infrared spectrophotometer. Light transmittance at 1276 nm increased by 37.3% and 41.1% at 60 min after the treatment in the cases with 40%PG5%A o and 40%G5%A w, respectively. Diffuse reflectance at 1066 nm decreased by 20.6% and 29.3% at 60 min after the treatment with 40%PG5%A o and 40%G5%A w, respectively. Forty percent glycerol or propylene glycol with the addition of Azone could achieve the same optical clearing effect as 80% glycerol. The results indicated that skin optical clearing with the topical application of glycerol and propylene glycol was markedly enhanced by both water-soluble and oil-soluble Azone. Skin penetration enhancing effect of Azone accounts probably for the skin clearing enhancement. In addition, Azone itself has shown optical clearing capability.

Stably anodic green electrochromic aromatic poly(amine–amide–imide)s: Synthesis and electrochromic properties

A series of new poly(amine–amide–imide)s with pendent 4-methoxy-substituted triphenylamine (TPA) units having inherent viscosities of 0.35–0.45 dL/g were prepared from various aromatic bis(trimellitimide)s and the 4-methoxy-substituted triphenylamine-based aromatic diamine, 4,4′-diamino-4″-methoxytriphenylamine ( I), by direct polycondensation. All the polymers are readily soluble in polar organic solvents. Flexible and amorphous films of these poly(amine–amide–imide)s could be obtained by solution-casting, and showed excellent thermal stability, 10% weight-loss temperatures in excess of 515 °C, and char yields at 800 °C in nitrogen higher than 58% associated with high glass-transition temperatures (297–305 °C). These polymers exhibited a maximum UV–vis absorption at 302–304 nm with fluorescence emission maxima around 360–376 nm in N-methyl-2-pyrrolidinone (NMP) solution. The hole-transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the poly(amine–amide–imide) films cast onto an indium–tin oxide (ITO)-coated glass substrate exhibit a reversible oxidation at 0.79–0.80 V vs. Ag/AgCl in acetonitrile solution, and reveal good stability of electrochromic characteristics with a color change from yellow to green at applied potentials ranging from 0.00 to 0.95 V. These anodically polymeric electrochromic materials not only showed excellent reversible electrochromic stability with good green coloration efficiency (CE = 395 cm 2/C) but also exhibited high contrast of optical transmittance change (Δ T%) up to 78% in 768 nm. After over 100 cyclic switches, the polymer films still exhibited stable electrochromic characteristics.

Synthesis and electrochromism of novel organosoluble polyarylates bearing triphenylamine moieties

AbstractA series of novel aromatic polyarylates with triphenylamine units in the main chain and as the pendent group were prepared from the dicarboxylic acid monomer, N,N‐bis(4‐carboxyphenyl)‐N′, N′‐diphenyl‐1,4‐phenylenediamine (1), and various bisphenols. These polyarylates were amorphous and readily soluble in common organic solvents. They had excellent levels of thermal stability associated with moderately high Tg values (182–263 °C). These polymers exhibited strong UV–vis absorption bands at 357–360 nm in toluene solution and the photoluminescence spectra showed maximum bands around 493–503 nm in the green region. The hole‐transporting and electrochromic properties were examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyarylates exhibited two reversible oxidation redox couples in acetonitrile solution at Eonset 0.77–0.79 V and 1.12–1.14 V, respectively. The typical polymer 3b film revealed good stability of electrochromic characteristics, with color change from colorless to green and blue at applied potentials ranging from 0.00 to 1.24 V. These anodically polymeric electrochromic materials not only showed excellent reversible electrochromic stability with good green coloration efficiency (CE = 159 cm2/C) and blue coloration efficiency (CE = 154 cm2/C) but also exhibited high contrast of optical transmittance change (ΔT%), 54% in 895 nm for green color and up to 84% in 595 nm for blue color. After over 100 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2004–2014, 2007

Highly stable anodic green electrochromic aromatic polyamides: synthesis and electrochromic properties

A 4-methoxy-substituted triphenylamine containing the aromatic diamine, 4,4′-diamino-4″-methoxytriphenylamine (2), was synthesized by the caesium fluoride-mediated condensation of p-anisidine with 4-fluoronitrobenzene, followed by palladium-catalyzed hydrazine reduction of the dinitro intermediate. A series of new polyamides with pendent 4-methoxy-substituted triphenylamine (TPA) units having inherent viscosities of 0.27–1.39 dL g−1 were prepared via the direct phosphorylation polycondensation of various dicarboxylic acids and the diamine (2). All the polymers were readily soluble in many organic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc), and could be solution-cast into tough and flexible polymer films. These aromatic polyamides had useful levels of thermal stability associated with their relatively high softening temperature (242–282 °C), 10% weight-loss temperatures in excess of 470 °C, and char yields at 800 °C in nitrogen higher than 60%. The hole-transporting and electrochromic properties are examined by electrochemical and spectroelectrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium-tin oxide (ITO)-coated glass substrate exhibited reversible oxidation at 0.73–0.79 V versus Ag/AgCl in acetonitrile solution, and revealed excellent stability of electrochromic characteristics with a color change from colorless to green at applied potentials ranging from 0.00 to 1.05 V. These anodically polymeric electrochromic materials not only showed excellent reversible electrochromic stability with good green coloration efficiency (CE = 374 cm2 C−1) but also exhibited high contrast of optical transmittance change (ΔT %) up to 85% at 787 nm and 30% at 391 nm. After over 1000 cyclic switches, the polymer films still exhibited excellent stability of electrochromic characteristics.

Control of liquid crystal alignment by deposition of silicon oxide thin film

We investigated liquid crystal alignment on a-SiO x thin films by means of X-ray diffraction and X-ray photoemission spectroscopy as we varied the deposition temperature and the target-to-substrate distance. We found that liquid crystal molecules can be aligned vertically on a-SiO x film when the stoichiometry parameter x of a-SiO x is smaller than 1.56, but they can be aligned homogeneously when x is larger than 1.56. We also found that whether liquid crystals can be aligned vertically or homogeneously on a-SiO x film can be predicted simply by measuring the change in optical transmittance by deposition of a-SiO x thin film layers.

Kinetics of Radiation Damage of Quartz Glass by Low-Energy Protons

In a ground-based simulation of the space environment of high vacuum, heat sink, and low-energy protons (140 keV), the change in optical transmittance of JGS3 optical quartz glass was studied, and a kinetic model for the evolution of color centers in the process of radiation damage was explored. Experimental results show that radiation damage effects obviously occur in the surface layer of quartz glass under high-flux and low-energy proton radiation. The optical density change increases rapidly and then a saturation trend appears with increasing absorption dose. Based on experimental results, a kinetic model for the evolution of color centers in quartz glass irradiated with protons is proposed, and the change in optical density is given. The fitted curve is similar to experimental ones. It is believed that the proposed kinetic model can be used in the quantitative description of the change in optical properties of quartz glass increasing absorption dose under low-energy proton radiation.

Au and NiO nanocrystals doped into porous sol–gelSiO2 films and the effect on optical CO detection

Thin-film composites comprised of NiO and NiO/Au nanoparticles in a porousSiO2 matrix have been prepared using the sol–gel technique. When at elevated temperatures(200 °C<T<350 °C) and exposed to carbon monoxide, the films undergo reversible changes in opticaltransmittance at wavelengths in the visible–near IR region. For NiO composite films heated at330 °C and exposed to 1% CO in air, there is an increase in transmittance which approaches 2–4%over most of the visible range. For NiO/Au composite films the transmittance increaseexhibits a wavelength dependence, with a maximum change which is close to 6% atλ≈630 nm and which is close to zero in the Au plasmon resonance range(λ≈550 nm).

Hemodialysis monitoring in whole blood using transmission and diffuse reflection spectroscopy: a pilot study

Visible and near infrared transmission and diffuse reflection spectroscopy were used to monitor changes in whole blood resulting from hemodialysis treatment for end-stage renal disease. Blood samples from 8 patients on chronic hemodialysis therapy were measured in the 500- to 1700-nm wavelength range immediately before and after a single treatment. Principal component scores characteristic of each spectrum were derived, and mean pre- and posttreatment scores of the first principal component indicated a significant treatment-dependent change in both optical transmission (P = 0.004) and diffuse reflection (P < 0.001). Significant treatment-induced change persisted (P < 0.05) when the first four principal components were used to account for >97% of the treatment-dependent spectral variation. Some blood spectral changes expressed in terms of difference spectra (posttreatment - pretreatment) were consistent with standard clinical indicators of weight reduction, urea reduction, and potassium change, with probable origins at a molecular level. The results indicate the feasibility of using optical transmission and diffuse reflection spectroscopy to characterize clinically relevant blood changes for the future development of more comprehensive indicators of hemodialysis efficacy and long-term clinical outcomes. Moreover, the optical techniques employed are adaptable for potential online monitoring of blood changes during the hemodialysis treatment.

Optical and Electrical Properties of Mg ∕ Ni Alloy Subjected to Electrochemical Hydrogenation

The work is aimed at studying properties of the Mg–Ni alloy thin film during electrochemical hydrogenation in an alkaline electrolyte. We have simultaneously measured the kinetics of the cathodic processes under galvanostatic conditions and changes in optical transmission. We have performed in situ ac impedance measurements of gradually hydrogenated films to monitor changes in their electrical properties. Mg–Ni alloys demonstrate high optical contrast during electrochemical hydrogenation due to switching between reflective and transparent states, excellent reversibility of the hydrogenation–dehydrogenation reaction, and fair service time. The value of the ac impedance technique for studying the complex electrical processes accompanying the incorporation of hydrogen into active metals and alloys is demonstrated.

How Can Azobenzene Block Copolymer Vesicles Be Dissociated and Reformed by Light?

The underlying mechanism of UV light-induced dissociation and visible light-induced reformation of vesicles formed by an azobenzene diblock copolymer was investigated. These processes were studied in situ by monitoring changes in optical transmittance of the vesicular solution while being exposed to UV or visible light irradiation. The results indicate that the UV-induced dissociation of the vesicles results from their thermodynamic instability due to a shift of the hydrophilic/hydrophobic balance arising from the trans-cis isomerization, while their reaggregation takes place upon visible light irradiation that shifts the hydrophilic/hydrophobic balance in the opposite direction after the reverse cis-trans isomerization. The study suggests a specific design principle for obtaining UV light-dissociable and visible light-recoverable vesicles based on azobenzene block copolymers. On one hand, the structure of azobenzene moiety used in the hydrophobic block should have a small (near zero) dipole moment in the trans form and a significantly higher dipole moment in the cis form, which ensures a significant increase in polarity of the hydrophobic block under UV light irradiation. On the other hand, the hydrophilic block should be weakly hydrophilic. The conjunction of the two conditions can make the light-induced shift of the hydrophilic/hydrophobic balance important enough to lead to the reversible change in vesicular aggregation.

Optical vibration sensor fabricated by femtosecond laser micromachining

We fabricated an optical vibration sensor using a high-repetition rate femtosecond laser oscillator. The sensor consists of a single straight waveguide written across a series of three pieces of glass. The central piece is mounted on a suspended beam to make it sensitive to mechanical vibration, acceleration, or external forces. Displacement of the central piece is detected by measuring the change in optical transmission through the waveguide. The resulting sensor is small, simple, and requires no alignment. The sensor has a linear response over the frequency range 20 Hz–2 kHz, can detect accelerations as small as 0.01m∕s2, and is nearly temperature independent.

Optical transmission through inelastically deformed shocked sapphire: stress and crystal orientation effects

Plane shock wave experiments were performed to examine optical transmission in sapphire single crystals (c cut, a cut, and r cut) compressed to longitudinal stresses ranging between 119 and 260kbar. Peak stress and particle velocity values in our experiments were obtained by compiling and analyzing published continuum data on shocked sapphire crystals. Time-resolved measurements, with nanosecond resolution, showed time-, stress-, and orientation-dependent changes in optical transmission beyond the Hugoniot elastic limit. Over the 300–680-nm range examined in our work, no wavelength dependence was observed. Loss of optical transmission in the stress range examined is due to inelastic deformation in shocked sapphire crystals. The present data reveal that inelastic deformation mechanisms are different in r-cut sapphire compared to a-cut and c-cut sapphire, and may be different for all three orientations examined. Although quantitative analysis of the time-dependent optical transmission data is not possible at present, optical transmission results have provided insight into inelastic deformation mechanisms in shocked sapphire. Present results are expected to be valuable for use of sapphire windows in shock wave experiments.

Effects of Annealing on Chemical Composition, Crystallinity, Optical Transmission and Electrical Conductivity of ZnO Thin Films Prepared on Glass Substrates by Chemical Bath Deposition

The effects of annealing on the chemical composition and other properties of ZnO thin films prepared on glass substrates by chemical bath deposition are described. The atomic ratio [Zn]:[O] of the unannealed film measured by electron probe X-ray microanalysis (EPMA) is 45:55, lower than the ideal ratio 50:50. It gradually increases toward the ideal ratio with increasing annealing temperature up to 500°C. The change in the atomic ratio [Zn]:[O] is interpreted to be due to the content of remaining Zn(OH)2, whose existence in films is determined by the analysis of the O1S peak in X-ray photoelectron spectroscopy (XPS) spectra, that decreases with increasing annealing temperature. The increase in electrical conductivity is observed on annealed films. This is also interpreted to be due to the decrease in the content of remaining Zn(OH)2. Notable changes in crystallinity and optical transmission by annealing are not observed.

Quantification of Gas-Phase H-Atom Number Density by Tungsten Phosphate Glass

It is shown that H-atom densities in the gas phase can be evaluated by simply measuring the change in optical transmittance of tungsten phosphate glass plates. Tungsten oxide (WO3) doped in phosphate glass plates can be reduced by exposure to H atoms and the degree of reduction can be evaluated from the change in their optical transmittance. The difference in the logarithms of the transmittances before and after the reduction showed a linear dependence on the H-atom density evaluated by a vacuum-ultraviolet laser absorption technique. No change in the transmittance was observed in the absence of H atoms, showing that reduction of WO3 by H2 molecules can be ignored.