Bottom Illumination Research Articles

A smartphone-based colorimetric reader for bioanalytical applications using the screen-based bottom illumination provided by gadgets.

A smartphone-based colorimetric reader (SBCR) was developed using a Samsung Galaxy SIII mini, a gadget (iPAD mini, iPAD4 or iPhone 5s), integrated with a custom-made dark hood and base holder assembly. The smartphone equipped with a back camera (5 megapixels resolution) was used for colorimetric imaging via the hood and base-holder assembly. A 96- or 24-well microtiter plate (MTP) was positioned on the gadget's screensaver that provides white light-based bottom illumination only in the specific regions corresponding to the bottom of MTP's wells. The pixel intensity of the captured images was determined by an image processing algorithm. The developed SBCR was evaluated and compared with a commercial MTP reader (MTPR) for three model assays: our recently developed human C-reactive protein sandwich enzyme-linked immunosorbent assay (ELISA), horseradish peroxidase direct ELISA, and bicinchoninic acid protein estimation assay. SBCR had the same precision, dynamic range, detection limit and sensitivity as MTPR for all three assays. With advanced microfabrication and data processing, SBCR will become more compact, lighter, inexpensive and enriched with more features. Therefore, SBCR with a remarkable computing power could be an ideal point-of-care (POC) colorimetric detection device for the next-generation of cost-effective POC diagnostics, immunoassays and diversified bioanalytical applications.

Nonlinear optical point light sources through field enhancement at metallic nanocones.

A stable nonlinear optical point light source is investigated, based on field enhancement at individual, pointed gold nanocones with sub-wavelength dimensions. Exciting these cones with near-infrared, focused radially polarized femtosecond beams allows for tip-emission at the second harmonic wavelength (second harmonic generation, SHG) in the visible range. In fact, gold nanocones with ultra-sharp tips possess interesting nonlinear optical (NLO) properties for SHG and two-photon photoluminescence (TPPL) emission, due to the enhanced electric field confinement at the tip apex combined with centrosymmetry breaking. Using two complementary optical setups for bottom or top illumination a sharp tip SHG emission is discriminated from the broad TPPL background continuum. Moreover, comparing the experiments with theoretical calculations manifests that these NLO signatures originate either from the tip apex or the base edge of the nanocones, clearly depending on the cone size, the surrounding medium, and illumination conditions. Finally, it is demonstrated that the tip-emitted signal vanishes when switching from radial to azimuthal polarization.

Moon phase effects and timing of emerging macrobenthic assemblages in a sheltered soft-bottom sublittoral habitat

Several species of benthic macro and meio-invertebrates actively emerge from the seabed to the water column during the night. Such diel vertical migrations have important consequences for benthic–pelagic coupling, dispersal, connectivity and recovery after disturbance of benthic assemblages. However, this process has never been studied in the coast of the Humboldt Current ecosystem. Herein we examined the relationship between the emerging assemblage and moon phases (and co-variables) and the timing of emergence during the day/night cycle, in a sublittoral soft-bottom habitat. Sampling using emergence traps was conducted at 7m depth in the zone of Bolsico, a sheltered cove with low bottom hydrodynamics in northern Chile. Multivariable analysis showed that changes in the dissimilarity of the emerging assemblage were related to each moon phase. The percentage of moon illumination, bottom illumination and tide amplitude explained most of the variation of the emerging assemblage. Species showed differential responses to each moon phase; some were abundant at intermediate phases (e.g., harpacticoids), or peaked at full moon (e.g. ostracods) and others such as mysids emerged in equal abundances at all moon phases. The timing of assemblage emergence followed a consecutive sequence through the night/day period. Most of the studies dealing with the emergence processes have described species-specific responses. Our research shows that the examination at assemblage level may reveal new and distinct patterns of emergence in sublittoral soft-bottom habitats.

A transparent Pyrex μ-reactor for combined in situ optical characterization and photocatalytic reactivity measurements

A new Pyrex-based μ-reactor for photocatalytic and optical characterization experiments is presented. The reactor chamber and gas channels are microfabricated in a thin poly-silicon coated Pyrex chip that is sealed with a Pyrex lid by anodic bonding. The device is transparent to light in the UV-vis-near infrared range of wavelengths (photon energies between ~0.4 and ~4.1 eV). The absorbance of a photocatalytic film obtained with a light transmission measurement during a photocatalytic reaction is presented as a proof of concept of a photocatalytic reactivity measurement combined with in situ optical characterization. Diffuse reflectance measurements of highly scattering photocatalytic nanopowders in a sealed Pyrex μ-reactor are also possible using an integrating sphere as shown in this work. These experiments prove that a photocatalyst can be characterized with optical techniques after a photocatalytic reaction without removing the material from the reactor. The catalyst deposited in the cylindrical reactor chamber can be illuminated from both top and bottom sides and an example of application of top and bottom illumination is presented.

P‐178: Semi‐transparent Tandem Device Comprising Organic Light‐emitting Diodes and Organic Solar Cell

AbstractSemitransparent stacked device consisting of an OLED and an OSC was demonstrated connected by a thin Ag as the connecting unit, which was modified by self‐assembled monolayer (SAM). Efficiency of OSC‐mode from the bottom and top illumination is 0.36% and 0.27%, respectively, while current efficiency of OLED‐mode from the bottom‐ and top‐emission is 3.0 and 1.2 cd/A.

Photophysics of Solution-Processed Transparent Solar Cells Under Top and Bottom Illumination

Semitransparent organic bulk-heterojunction solar cells based on poly(3-hexylthiophene) (P3HT):phenyl-C -butyric acid methyl ester (PCBM) with a bottom indium tin oxide (ITO) and semitransparent top metal electrode are presented. The solar cell devices are characterized under two different conditions-top illumination and bottom illumination. The photovoltaic performance is compared with a bottom-illuminated reference device having a fully reflecting aluminum electrode. Optical simulations based on the transfer matrix approach were performed in order to understand the device physics of these semitransparent solar cells. We found that unlike bottom illumination, the exciton generation in top-illuminated devices takes place close to the metal electrode giving rise to high recombination losses in such devices.

All-spin-coating vacuum-free processed semi-transparent inverted polymer solar cells with PEDOT:PSS anode and PAH-D interfacial layer

Semi-transparent inverted polymer solar cells (PSCs) were fabricated by all-spin-coating vacuum-free process. An interfacial layer of poly(allylamine hydrochloride) and dextran (PAH-D) was introduced to modify the surface wettability of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) film for depositing aqueous-solution-processed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (CLEVIOS™ PH500) (PH500) anode as well as enhancing the adhesion and bonding strength between the active layer (P3HT:PCBM) and conducting polymer electrode (PH500). The photovoltaic performance of the semi-transparent PSCs under top and bottom illumination was investigated and the highest PCE of about 1.86% was achieved under simulated AM 1.5 illumination (100 mW/cm 2) from the bottom side with a reflective white paper back side. The semi-transparent Cell A have the potential for use as energy-generating color window glasses as well as the subcell of tandem solar cells. The all-spin-coating vacuum-free processing provides a possibility of high-throughput all-solution-processed fabrication of PSCs by roll-to-roll processing.

Tip-enhanced single molecule fluorescence near-field microscopy in aqueous environment

For nanobiophysical applications, scanning near-field optical microscopy must combine high optical resolution and single fluorescent molecule sensitivity with the ability to operate in aqueous solution. These requirements can be achieved using the electric field enhancement at the tip of illuminated silicon probes for atomic force miscroscopy (AFM), whereby single ATTO-740 dye molecules could be imaged at an optical resolution down to 20 nm under ambient conditions as well as in aqueous solution. Two illumination modes have been tested: (a) bottom illumination in a total internal reflection microscopy setup and (b) direct top illumination, both with dedicated phase-sensitive single photon counting technology in dynamic AFM mode of operation.

A study of the dynamic properties of photo-induced charge carriers at nanoporousTiO2/conductive substrate interfaces by the transient photovoltage technique

Two interfaces with opposite orientations of the built-in electric field, nanoporousTiO2 film/ FTO electrodeand nanoporous TiO2 film/semitransparent Pt substrate, were constructed. The separation andtransport of photo-induced charge carriers in the two systems of nanoporousTiO2/conductive substrate were studied by the transient photovoltage technique. Various transient photovoltageresponses were obtained when the laser beam was incident from the surface of the nanoporousTiO2 film (topillumination) or the TiO2/substrate interface (bottom illumination). A linear and a logarithmic dependence ofthe photovoltage amplitude on the excitation level were observed for topillumination and bottom illumination, respectively. The results indicate thatdiffusion is the major way for the separation of charge carriers in the nanoporousTiO2 film and that the excess carriers were separated by drift under the built-in electric field at theTiO2/substrate interfaces.

High Quality Hot-wire Microcrystalline Silicon for Efficient Single and Multijunction N-i-p Solar Cells

AbstractIn this paper, the potential of hot-wire chemical vapor-deposited (HWCVD) microcrystalline silicon (μc-Si) for use in solar cells is explored. Incorporation of the material in the current-limiting bottom cell of two tandem cells on plain stainless steel resulted in FF values as high as 0.77, which is much higher than the highest single junction FF. A combination of experiments, calculations and computer simulations was employed to identify causes for the observed high tandem cell FF values. Both the light intensity and the spectral composition of the bottom cell illumination in a tandem were found to contribute to an increase of the bottom cell FF. The fact that the operational voltage of a tandem cell is higher than that of the current-limiting subcell, was calculated to lead to a tandem FF that can be far higher than that of the limiting cell. Com-puter simulations with the AMPS computer code show that the current mismatch in a tandem cell reduces the recombination in the current-limiting cell, possibly by slightly enhancing the internal field of that cell. Use of a 1.5 μm ìc-Si:H hot-wire deposited absorber layer in a single junction cell on a textured back reflector yielded a Voc, FF and Jsc of 0.543 V, 0.656 and 23.60 mA/cm2, respectively, which combine to an 8.4 % record efficiency for μc-Si single junction n-i-p cells with a hot-wire intrinsic layer.

Illumination and turbidity effects on observing faceted bottom elements with uniform Lambertian albedos

Aircraft images were collected near Lee Stocking Island (LSI), Bahamas, with wavelike features for bright sand bottoms during times when solar zenith angles were large. The image contrast between leading and trailing wave facets approached a 10–15% difference because of algae accumulations in wave troughs or topographic variations of the bottom. Reflectance contrast for blue light was greater than for red and green wavelengths when algae or detritus was present in the troughs. However, the contrast at green and red wavelengths was greater than at blue wavelengths when caused by the interplay between bottom topography and oblique illumination. A three‐dimensional backwards Monte Carlo (BMC) model was developed to evaluate the effect of oblique illumination on wavelike topographic features for various values of water clarity and bottom albedo. An inverse optical modeling approach, previously developed for flat, horizontally homogeneous bottoms, was applied to the BMC results. Bathymetric estimates for bright facets tilted 10° toward the sun were slightly smaller than actual depths, whereas shaded facet depth estimates were too high by about 5%. Larger errors were associated with albedo retrievals, where shaded facets produced albedo estimates up to 15% lower than actual values. Errors increased with tilt angles up to 20° but decreased with sea and sky turbidity. Averaging sunlit and shaded pixels before running the inverse model reduced the uncertainty of bathymetric and albedo estimates to about 2 and 5%, respectively, comparable to previous field evaluations of the inversion model.

Stereoselective Disposition of Sustained Release Microspheres of Ibuprofen Enantiomers in Rats: II. Acute Gastrointestinal Toxicity

The purpose of this study was to examine acute gastrointestinal tract (GIT) toxicity caused by the pure enantiomers of ibuprofen in male Wistar rats. A 2 2 2 factorial design in which rats were randomly divided into eight experimental groups and a control group was used. They were dosed with the sustained release microsphere and conventional suspensions of ibuprofen enantiomers at 20 mg/kg and 40 mg/kg dose levels. Bethanechol chloride (5 mg/kg), a cholinomimetic agent, was administered 30 min after dosing to induce gastric irritation. Animals were euthanized at different time intervals up to 48 hr postdosing followed by excision of stomach and intestinal tract. Blood samples also were collected during this study by cardiac puncture and stereospecifically analyzed. Tissues were examined for lesions and hemorrhages macroscopically (75 magnification) using top and bottom illumination. Macroscopic evaluation of the tissue samples revealed significant differences in the GIT toxicity caused by S- and R-ibuprofen at the 40 mg/kg level (p < . 05), with S-ibuprofen being the more toxic form. Toxicity seen in the R-ibuprofen formulation may be both inherent and due to subsequent inversion to S-enantiomer. Toxicity was reduced significantly with the higher dose (40 mg/kg) of the encapsulated drug compared with the unencapsulated drug. At the 20 mg/kg dose level, no significant differences were observed between the two enantiomers. At this dose, encapsulation reduced toxicity but not significantly compared with unencapsulated ibuprofen. GIT toxicity was site-specific; high toxicity was seen in the stomach, very little toxicity was seen in the duodenum and jejunum, whereas relatively higher toxicity was observed in the ileum. High toxicity also was seen in the cecum and colon, evidenced by cecal ulcers. Monitoring plasma concentrations revealed that enough drug was released enough to subject GI mucosa to irritation. In all cases, the plasma concentrations and the AUC were higher for S- compared with R-ibuprofen. However, there was no correlation between the plasma levels and the toxicity seen in the GIT. A previous 7-hr study, carried out in our lab to assess GIT toxicity of racemic ibuprofen, showed that the racemate was more ulcerogenic at equivalent doses and within the same time interval. Encapsulation of ibuprofen significantly reduced GIT toxicity especially at the higher doses. S-ibuprofen caused greater toxicity compared with R-ibuprofen and GIT toxicity was site-specific. Greater toxicity caused by racemic ibuprofen has significant clinical implications.

Illumination in first feeding tanks for marine fish larvae

Illumination levels were measured in three artificially illuminated tanks (a black tank, a white tank and a tank with black sides and white bottom) in order to test how well normal tank illumination in different tank types corresponds to natural illumination conditions for first feeding of marine fish larvae. Measurements were made with clear water and with algae added (‘green water’). The black tank had low wall and bottom illumination. The white tank had high wall and bottom illumination. The black-walled white-bottomed tank had low wall and high central and bottom illumination. Green water attenuated light substantially. The black tank seemed best suited to reproduce natural illumination conditions. The white tank was not suited. The black-walled white-bottomed tank had interesting properties, but species specific tests would have to be carried out to fine tune the reflective properties of the bottom. Green water seemed to be beneficial in all tests.

GaAs/AlGaAs multiquantum well infrared detector arrays using etched gratings

Efficient coupling of long-wavelength infrared (LWIR) radiation to a two-dimensional (2-D) array of GaAs/AlGaAs multiple quantum well detectors is achieved by illumination through chemically etched diffraction gratings. Gratings were fabricated on the back surface of the GaAs substrate as well as selectively on the top contact of the detector mesas. Both top and bottom illumination schemes were employed. In all cases, high coupling efficiency (&amp;gt;90%) of the gratings was observed as measured by comparing the responsivity to that of an identical detector illuminated through an angle-polished facet. The results demonstrate the feasibility of high-sensitivity GaAs LWIR imagers.

A simple mask aligner and printing frame for conformable photomask lithography

Conformable photomask lithography allows submicrometer lines to be replicated by contact printing. Surface acoustic wave devices with 0.4-µm lines have been produced using this technique. A mask aligner and printing frame have been designed which feature micrometer controlled X and Y motion, rotation about the center of the viewing field, and both top and bottom illumination of mask and substrate. The construction and use of the apparatus, which is based on a toolmaker's microscope, is fully described.

A novel methodology for radiative transfer in a planetary atmosphere

A novel methodology for evaluating the field of anisotropically scattered radiation within a homogeneous slab atmosphere of arbitrary optical thickness is provided. It departs from the traditional radiative transfer approach in first considering that the atmosphere is illuminated by an isotropic light source. From the solution of this problem, it subsequently proceeds to that for the more conventional case of monodirectional illumination. The azimuthal dependence of the field is separated in the usual manner by an harmonic expansion, leaving a problem in four dimensions (τ=optical depth, τ0=thickness, ζ, η=directions of incidence and scattering) which, as is well known, is numerically extremely inconvenient. Two auxiliary radiative transfer formulations of increasing dimensionality are considered: (i) a transfer equation for the newly introduced functionbm(τ,η,τ0) with Sobolev's functionΦm(τ,τ0) playing the role of a source-function. Because the incident direction does not intervene,Φm is simply expressed as a single integral term involvingbm. For bottom illumination, an analogous equation holds for the other new functionhm(τ,η,τ0). However, simple reciprocity relations link the two functions so that it is only necessary to considerbm; (ii) a transfer equation for the other new functionam(τ,η,ζ,τ0) with a source-function provided by Sobolev's functionDm(τ,ζ,τ0). For bottom illumination, another functionfm(τ,η,ζ,τ0) is introduced; by a similar argument using reciprocity relations,fm is reduced toam rendering necessary only the consideration ofam. However, a fundamental decomposition formula is obtained which shows thatam is expressible algebraically in terms of functions of a single angular variable. The functionsΦm andDm are shown to be the values in the horizontal plane ofbm andam, respectively. The other auxiliary functionsXm andYm are also expressed algebraically in terms ofbm. These results enable one to proceed to the final step of evaluating the radiation field for monodirectional illumination. The above reductions toalgebraic relations involving only the functionbm appear to be more advantageous than Sobolev's (1972) recent approach; they also circumvent some basic numerical difficulties in it. We believe the present approach may likewise prove to be superior to most (if not all) other methods of solution known heretofore.