Fluorescent Sources Research Articles

Oxidation of Chitosan in Solution by Photocatalysis and Product Characterization

Chitosan (CS) was oxidized under mild conditions in solution via photocatalysis using a 45-W compact household fluorescent light source in the presence of an immobilized TiO2 film. The physicochemical properties of the original and oxidized CS solutions were characterized by ultraviolet–visible (UV–Vis) spectroscopy, 13C nuclear magnetic resonance spectroscopy, differential scanning calorimetry, Fourier-transform infrared spectroscopy, elemental analysis, pH-potentiometric titration, and gel permeation chromatography. The results showed that CS was effectively oxidized within 4 h of irradiation as indicated by colour changes of the product with the appearance of a new UV–Vis absorption band at 337.7 nm. The results support the formation of carbonyl groups along with negligible change in the polymer chain structure of CS and/or chain scissioning effects. The photocatalysis reported herein is a convenient, feasible and environmentally friendly method for oxidation of natural biopolymers such as CS in solution.

Metal-enhanced fluorescence of graphene oxide by palladium nanoparticles in the blue–green part of the spectrum

Graphene oxide (GO) has a wide fluorescence bandwidth, which makes it a prospective candidate for numerous applications. For many of these applications, the fluorescence yield of GO should be further increased. The sp2-hybridized carbons in GO confine the π-electrons. Radiative recombination of electron–hole pairs in such sp2 clusters is the source of fluorescence in this material. Palladium nanoparticles are good catalysts for sp2 bond formations. We report on the preparation of GO, palladium nanoparticles and their nanocomposites in two different solvents. It is shown that palladium nanoparticles can considerably enhance the intrinsic fluorescence of GO in the blue–green part of the visible light spectrum. Fluorescence enhancement has been attributed to the catalytic role of palladium nanoparticles in increasing the number of sp2 bonds of GO with the molecules of the surrounding media. It is shown that palladium nanoparticles could be the nanoparticle of choice for fluorescence enhancement of GO because of their catalytic role in sp2 bond formation.

Waste heat recovery in solid-state lighting based on thin film thermoelectric generators

The waste heat of high-power light emitting diodes (LEDs) is well localized and can be efficiently harvested in contrast to incandescent or fluorescent light sources. Compact thin film thermoelectric generators can accumulate the high-density heat flux from the LED chip and convert it into usable electrical power. We designed and analyzed a thermal management setup with high power LED and embedded thin film thermoelectric generators. The available thermal gradient of approximately 50K allows conversion of the LED waste heat with an overall efficiency of 1%. We present an application of the active cooling powered by the harvested waste heat. The compact flat shape of the thin film thermoelectric generators allows an instant upgrade of the existing LED-based luminaries available on the market.

Determination of pressure from measured Raman frequency shifts of anhydrite and its application in fluid inclusions and HDAC experiments

A new geobarometry was derived from the quantified relationships among Raman vibrational frequencies of anhydrite, pressure and temperature, as determined from in-situ micro-Raman spectroscopy of natural anhydrite crystals measured at p–T conditions up to 560°C and 1400MPa by using a hydrothermal diamond anvil cell (HDAC). With this geobarometry, the pressure in HDAC experiments and in anhydrite-bearing fluid inclusions can be determined directly from the ν1, 1016, ν3, 1128 and ν3, 1160 Raman frequency shifts of anhydrite at high p–T conditions relative to their values measured at ambient conditions. The pressure can be determined to an accuracy of better than 30MPa based on the attainable accuracy of ±0.1cm−1 for the fitted ν1 Raman peak positions, provided the measured spectra are calibrated using the emission peak of an external fluorescent light source. The feasibility and reliability of this geobarometry were verified by rebuilding the p–T history of two fluid inclusions from the ν1 frequency shifts of anhydrite daughter minerals from room to high temperatures, and by measuring the phase-transition pressures of calcite–CaCO3(II)–CaCO3(III) sequence at ambient temperature in a HDAC experiment using anhydrite as a Raman pressure sensor.

A 72 × 60 Angle-Sensitive SPAD Imaging Array for Lens-less FLIM.

We present a 72 × 60, angle-sensitive single photon avalanche diode (A-SPAD) array for lens-less 3D fluorescence lifetime imaging. An A-SPAD pixel consists of (1) a SPAD to provide precise photon arrival time where a time-resolved operation is utilized to avoid stimulus-induced saturation, and (2) integrated diffraction gratings on top of the SPAD to extract incident angles of the incoming light. The combination enables mapping of fluorescent sources with different lifetimes in 3D space down to micrometer scale. Futhermore, the chip presented herein integrates pixel-level counters to reduce output data-rate and to enable a precise timing control. The array is implemented in standard 180 nm complementary metal-oxide-semiconductor (CMOS) technology and characterized without any post-processing.

Time-of-flight secondary ion mass spectrometry to assess spatial distribution of A2E and its oxidized forms within lipofuscin granules isolated from human retinal pigment epithelium.

Lipofuscin granules accumulate in the cells of retinal pigment epithelium with age, particularly in patients with hereditary diseases. These granules are heterogeneous, being composed of mixtures of proteins and lipids, including more than 21 different fluorescent compounds. Bisretinoids and their photo-oxidation and photodegradation products represent the main source of lipofuscin fluorescence and exhibit phototoxic properties. This study used time-of-flight secondary ion mass spectrometry (ToF-SIMS) with in-depth probing to assess the depth distribution of N-retinylidene-N-retinylethanolamine (A2E) and its singly and doubly oxidized forms (A2E-ox and A2E-2ox, respectively) within lipofuscin granules and in their surface layer (lipid membrane). ToF-SIMS showed that A2E and its oxidized forms were uniformly distributed throughout lipofuscin granules but were not present at the membrane surface layer. This finding is important for understanding the process involved in the formation of lipofuscin granules and in their toxicity.

Effects of light intensity on metabolism and antioxidant defense in Haliotis discus hannai Ino

We examined the effects of light intensity on the metabolism, antioxidant enzymes, and expression of related genes in Haliotis discus hannai Ino, to determine the optimal lighting conditions for aquaculture of these animals. Succinate dehydrogenase activity was significantly lower after 48h in animals exposed to light intensities of 30 and 60μmol/m2/s, while lactate dehydrogenase activity and lactic acid content at 96h were significantly higher compared with animals in the dark or exposed to 5 or 15μmol/m2/s (both P<0.05). There was no significant difference in reactive oxygen species (ROS) contents between animals in the dark and those exposed to 5 or 15μmol/m2/s (P>0.05) throughout the experiment. However, ROS contents under light intensities of 30 and 60μmol/m2/s peaked at 12h, when expression levels of genes encoding catalase (CAT), thioredoxin peroxidase (TPX), sigma-glutathione-s-transferase (GSTS), and mu-glutathione-s-transferase (GSTm) also began to increase, and CAT and glutathione peroxidase (GPX) activities were significantly higher than in animals in the dark or exposed to 5 or 15μmol/m2/s (P<0.05). After a further 12h, the ROS content at 30μmol/m2/s began to decrease, and GPX activity and malondialdehyde (MDA) content also gradually decreased, followed by increases in ROS and MDA 48h later, to reach respective peaks at 96h. Gene expression levels of TPX, GSTS, GSTm, heat shock protein 70 (HSP70), and CAT began to decrease 72h later, suggesting that excessive accumulation of ROS may have caused oxidative damage to the tissues. At a light intensity of 60μmol/m2/s, expression levels of TPX, GSTS, GSTm, and HSP70 genes, total antioxidant capacity, and GPX activity peaked at 48h, and the ROS content was significantly higher than in any other group 48h later (P<0.05). However, gene expression levels of TPX, GSTS, GSTm, HSP70, HSP90, and CAT, and reduced glutathione content began to decrease, indicating that the antioxidant system had been unable to perform its normal physiological functions to withstand the long-term stress of adverse environmental factors. These results suggest that the light intensity should be controlled at 5–15μmol/m2/s during H. discus hannai aquaculture, to maintain the organism's normal physiological metabolism. Statement of relevanceThe disc abalone Haliotis discus hannai is an economically important shellfish in China, with demand growing for this high-protein and low-fat seafood. In 2014, 11,5397 tons of H.discushannai were harvested from aquacultural sources, but supply cannot currently meet consumer demand. In recent years, the natural habitat of H. discus hannai has declined as a result of overfishing, marine reclamation, water pollution, among others, leading to a sharp decrease in the numbers of H. discus hannai in the wild. Thus, the development of an aquacultural system for farming H. discus hannai, as well as for its protection in the wild, are a focus of current research.Light, including photoperiod, quality and intensity, is one of the key environmental factors influencing the growth, culture and survival of aquatic organisms. Over evolutionary time, organisms have evolved both physiological and behavioral mechanisms that enable them to adapt to diurnal fluctuations in light. In Chinese traditional abalone aquaculture, a sunshade net is usually used because of the photophobic nature of abalone. In particular, the aquaculturist usually provides a darkened setting for adult abalones to increase their food intake rate, facilitate their growth and promote gonadal development. For abalones in their natural environment, the light intensity in the water area is relatively stable, suggesting that there is a key regulative effect of light intensity on their growth and development.Gao et al. (2016a,b) found that a dark environment not only adversely affected the daily aquaculture production, but was also associated with a lower growth rate compared with animals reared under higher light intensities, because of lower food conversion efficiency and greater energy losses through excretion and feces. Physiological metabolism and antioxidant defense systems may therefore be key indicators for measuring the suitability of light intensity for aquaculture production. We therefore examined the effects of light intensity on the metabolism and antioxidant defense system, and on the expression of related genes, in H. discus hannai using a light-emitting diode (LED) to replace the conventional fluorescent light source. The results of this study will improve our understanding of the physiological tolerance and antioxidant defense characteristics of abalone under different light intensities, and enable the optimization of environmental light conditions in abalone aquaculture.

Multimodal optical coherence tomography and fluorescence lifetime imaging with interleaved excitation sources for simultaneous endogenous and exogenous fluorescence.

Multimodal imaging probes a variety of tissue properties in a single image acquisition by merging complimentary imaging technologies. Exploiting synergies amongst the data, algorithms can be developed that lead to better tissue characterization than could be accomplished by the constituent imaging modalities taken alone. The combination of optical coherence tomography (OCT) with fluorescence lifetime imaging microscopy (FLIM) provides access to detailed tissue morphology and local biochemistry. The optical system described here merges 1310 nm swept-source OCT with time-domain FLIM having excitation at 355 and 532 nm. The pulses from 355 and 532 nm lasers have been interleaved to enable simultaneous acquisition of endogenous and exogenous fluorescence signals, respectively. The multimodal imaging system was validated using tissue phantoms. Nonspecific tagging with Alexa Flour 532 in a Watanbe rabbit aorta and active tagging of the LOX-1 receptor in human coronary artery, demonstrate the capacity of the system for simultaneous acquisition of OCT, endogenous FLIM, and exogenous FLIM in tissues.

Mechanism of Fluorescence Switching in One ESIPT-Based Al(3+) Probe.

A recently synthesized Schiff base used as a probe for aluminum cations was studied with ab initio models. The primary reason for the lack of fluorescence in aprotic solvents was found to be the presence of an efficient conical intersection (CI) between the ground-states and the first singlet excited-states close to the Franck-Condon geometry. The excited-state pathway leading to this CI is barrierless but implies large amplitude motions, explaining why the fluorescence was observed in frozen acetonitrile matrix. Our calculations suggest that constraining the molecule by impending the rotation around the imino bond enables excited-state intramolecular proton transfer. A similar stiffening mechanism is responsible for the strong fluorescence turn-on after formation of complexes between Al(3+) cations and dehydrogenated Schiff base. Finally, the analysis of the possible fluorescence mechanisms in water indicates that the anion of 1 is the likely fluorescence source. Overall, this work allows one to disentangle the various origins of fluorescence switching in a probe.

Photostability study of commercial sunscreens submitted to artificial UV irradiation and/or fluorescent radiation

Sunscreens contain molecules with the ability to absorb and/or reflect UVA (ultraviolet A) and UVB (ultraviolet B) radiation, thereby preventing this radiation from reaching the epidermis or dermis. Their photo stabilities after exposure to UV radiation are well known and described, but there is little data on the stability of these filters after fluorescent indoors light radiation, such as from light emitted by commercial lamps present in homes and offices. Those lamps can expose people to varying levels of UVB, UVA, visible light, and IR (infrared). This study assesses the photostability of four different commercial products containing chemical sun filters after artificial UV and fluorescent irradiation, correlating the UVB and UVA absorption efficiencies of each product against the different types of radiation. The tested products were applied on a plate of polymethylmethacrylate (PMMA) and irradiated by a solar simulator with specific filters for UVA and UVB and a commercial fluorescent light source. According to the results, three formulations did not show photostability, suffering significant changes in their UV absorption spectra, and one of the selected formulations can be considered photostable. This reinforces the importance of conducting stability studies for sunscreen formulations in different conditions, including under artificial (indoor) light exposure.

Novel l 2,1-norm optimization method for fluorescence molecular tomography reconstruction.

Fluorescence molecular tomography (FMT) is a promising tomographic method in preclinical research, which enables noninvasive real-time three-dimensional (3-D) visualization for in vivo studies. The ill-posedness of the FMT reconstruction problem is one of the many challenges in the studies of FMT. In this paper, we propose a l 2,1-norm optimization method using a priori information, mainly the structured sparsity of the fluorescent regions for FMT reconstruction. Compared to standard sparsity methods, the structured sparsity methods are often superior in reconstruction accuracy since the structured sparsity utilizes correlations or structures of the reconstructed image. To solve the problem effectively, the Nesterov's method was used to accelerate the computation. To evaluate the performance of the proposed l 2,1-norm method, numerical phantom experiments and in vivo mouse experiments are conducted. The results show that the proposed method not only achieves accurate and desirable fluorescent source reconstruction, but also demonstrates enhanced robustness to noise.

Fluorescent Nanodiamonds for Molecular and Cellular Bioimaging

Fluorescent nanodiamonds (FNDs) have generated immense interest as fluorescent probes for biomedical imaging due to their unparalleled photostability and potential biocompatibility. Diamond can become fluorescent due to defects; in particular, nitrogen-vacancy (NV) centers in diamond are fluorescent sources with remarkable optical properties. FNDs containing NV centers do not photo-bleach or blink, their fluorescence emission can be modulated with a magnetic field making them one of the most sensitive magnetic field sensors, and they have fluorescence lifetime longer than fluorescent biomolecules. Commercial cost-effective availability along with method development for easy functionalization and imaging have promoted vigorous research on using FNDs as versatile bioimaging probes. Methods to coat FNDs with silica for easy functionalization for biomedical applications and to image FNDs background-free in vitro and in vivo by applying an alternating magnetic field with a conventional fluorescence microscope have been achieved. Functionalized FNDs have been used to track biomolecules in vitro and in vivo. For future use in humans and regulatory approval, it is necessary to study biodistribution, biotoxicity, and clearance, all of which have been studied in animals. This review gives an overview of the entire spectrum of FND related research.

Blind Source Separation Based on ICA Algorithm Applied to Multispectral Fluorescence Imaging

Immunofluorescence is one of the most used techniques in optical fluorescence microscopy and has substantial applications in biology and pathology. It aims to detect and localize one or more proteins thanks to the use of specific dyes. One of the major issues with immunofluorescence is the intrinsic fluorescence, called auto-fluorescence present in some biological specimen. Several approaches, based on blind source deconvolution, are developed to deal with this problem and to isolate the extrinsic fluorescence from the intrinsic one. In this paper, we present two Independent Component Algorithms based on second order and higher order statistics. Experimental results have revealed that the blind identification algorithm based on second-order statistics is more adaptedly fit to fluorescence sources un-mixing problem than algorithms based on higher-order statistics.

Quantum coherence of light emitted by two single-photon sources in a structured environment

We develop a theoretical framework for the analysis of the quantum coherence of light emitted by two independent single-photon sources in an arbitrary environment. The theory provides design rules for the control of the degree of quantum coherence, in terms of classical quantities widely used in nanophotonics. As an important example, we derive generalized conditions to generate superradiant and subradiant states of the emitters, and demonstrate the ability of a structured environment to induce long-range quantum coherence. These results should have broad applications in quantum nanophotonics, and for the sensing of fluorescent sources in complex environments.

Behavior of Broilers Reared under Monochromatic and Fluorescent Light Sources

Behavior of Broilers Reared under Monochromatic and Fluorescent Light Sources

Excitation efficiency of a side-pumped fiberized fluorescent dye microcapillary

Abstract In the present work we study the dependence of fluorescence spectra for different pump source characteristics on the length of a micro-capillary filled with a fluorescent dye solution. A standard fiber-optic glass ferrule with two parallel 125 μm inner diameter holes serving as capillary structures has been studied. One of the holes of the ferrule was filled with a solution of Rhodamine 6G in glycerin, while in the second hole an angle-polished single-mode pump optical fiber was placed. Experiments with pump fibers polished at 20°, 25°, 30°, 35°, 40° and 45° with a reflective aluminium coating have been conducted. The analysis of the experimental data shows differences in the behavior of the fluorescent spectra at different polished angles. Theoretical calculations for pump ray trajectories as well as overall power transmission for pump fibers polished at different angles have been made. The results show that the proposed construction could be used in optofluidic chemical and biosensors, microfluidic lasers or as a compact fluorescent source compatible with fiber-optic components.

Immobilized/P25/DSAT and Immobilized/Kronos/DSAT on Photocatalytic Degradation of Reactive Red 4 Under Fluorescent Light

In this work, photocatalytic degradation of Reactive Red 4 (RR4) using immobilized P25 and kronos were performed under fluorescent light sources. The photocatalysis activity for both catalysts was investigated under fluorescent lamp source which consist UV and Visible light. The effect of various parameters such as initial concentration, initial pH and strenght of immobilized plate were studied. The result showed that 90% of RR4 dye was degrade in 1 hr using immobilized/kronos/DSAT at 100 mg L -1 of RR4 dye while 81% degradation was achieved by immobilized/P25/DSAT at the same condition. The lowest pH showed the higher photocatalytic activity. Hence, the effect of dye concentration and pH on the photocatalysis study can be related with the behavior of environmental pollution. The low strength showed by immobilized/P25/DSAT where it remain 37 % as compared with strength of immobilized/kronos/DSAT (52 wt.%). For the future work, the polymer binder like Polyvinyl alcohol (PVA), Polyethylene glycol (PEG), and others polymers can be apply in immobilized study to overcome the strength problem.

Colour of Stone Slabs under Different Standard Illuminations

Spectral measurements have been carried out on polished stone slabs to show the accuracy of theoretical colorimetric calculations on perceptual differences of color appearance under various standard illuminations. Effects of the different spectral characteristics of the light source on colorization of the samples have been also studied to analyze the changes of color sensation on the samples in connection with the changes on the type of the illuminating source. Solar light (Standard Illuminant D65), basic incandescent source (Standard Illuminant A) and a basic fluorescent source (Standard Illuminant F11) have been tested on Tardos red limestone, Siklos green limestone, Carrara white and gray marbles and diorite samples. Colorizing effects of the examined illuminations are compared to Standard Illuminant E – the theoretically perfect white source.

Quasiparticle Transport in Thick Aluminum Films Coupled to Tungsten Transition Edge Sensors

We have fabricated and characterized test devices of a new geometry for cryogenic dark matter search superconducting sensors. The modified design uses the same photolithography masks used to fabricate earlier-generation devices, but with the Al and W films deposited in reverse order. This inverted film geometry (Al over W instead of our conventional W over Al) offers a simplified and robust way to dramatically increase the thickness of Al energy-collecting fins coupled to thin W-TESs—tungsten-transition edge sensors. Data are presented from experiments with inverted geometry test devices exposed to X-rays from a NaCl fluorescence source. The results are compared to data obtained with similar devices fabricated in the standard, non-inverted geometry.

Excitation of surface plasmon polariton modes with multiple nitrogen vacancy centers in single nanodiamonds

Nitrogen-vacancy (NV) centers in diamonds are interesting due to their remarkable characteristics that are well suited to applications in quantum-information processing and magnetic field sensing, as well as representing stable fluorescent sources. Multiple NV centers in nanodiamonds (NDs) are especially useful as biological fluorophores due to their chemical neutrality, brightness and room-temperature photostability. Furthermore, NDs containing multiple NV centers also have potential in high-precision magnetic field and temperature sensing. Coupling NV centers to propagating surface plasmon polariton (SPP) modes gives a base for lab-on-a-chip sensing devices, allows enhanced fluorescence emission and collection which can further enhance the precision of NV-based sensors. Here, we investigate coupling of multiple NV centers in individual NDs to the SPP modes supported by silver surfaces protected by thin dielectric layers and by gold V-grooves (VGs) produced via the self-terminated silicon etching. In the first case, we concentrate on monitoring differences in fluorescence spectra obtained from a source ND, which is illuminated by a pump laser, and from a scattering ND illuminated only by the fluorescence-excited SPP radiation. In the second case, we observe changes in the average NV lifetime when the same ND is characterized outside and inside a VG. Fluorescence emission from the VG terminations is also observed, which confirms the NV coupling to the VG-supported SPP modes.