Optical Fluorescence Spectroscopy Research Articles

Laser-induced breakdown spectroscopy application to control of the process of precious metal recovery and recycling

In this paper, we discuss the application of laser-induced breakdown spectroscopy to precious metal alloys used for the control of the process of recovery and recycling of scraps and waste of industrial processes. In particular, the possibility to obtain sensitivity and trueness comparable to the current systems used in industrial environment in the quantitative determination of the elements of interest was explored. The present study demonstrates that laser-induced breakdown spectroscopy can be considered as a viable alternative to inductively coupled plasma optical emission spectrometry and X-ray fluorescence spectroscopy for the determination of recovered precious metals. The limits of detection obtained are of the order of 0.2mg/g for all the elements considered. The maximum deviation with respect to the nominal concentrations is around 1mg/g at concentrations around 20mg/g (gold) corresponding to a relative error slightly higher than ±5%.

Durability of polymeric encapsulation materials for concentrating photovoltaic systems

ABSTRACTThe durability of polymeric encapsulation materials was examined using outdoor exposure at the nominal optical concentration of 500 suns. The results for 12 months' cumulative field deployment are presented for materials including ethylene‐co‐vinyl acetate, polyvinyl butyral (PVB), ionomer, polyethylene/polyoctene copolymer, thermoplastic polyurethane, poly(dimethylsiloxane), and poly(phenyl‐methyl siloxane). Measurements during the experiment included optical transmittance (direct and hemispherical), mass, visual appearance, and fluorescence spectroscopy in addition to the initial thermogravimetry of the materials. Measurements of the field conditions and ultraviolet dose at the test site were facilitated by numerous laboratory instruments; characterization of the specimen temperature was performed using thermography. Discovery experiments identified the importance of a secondary homogenizer optic and the importance of contamination control. To date, the formal experiment verified a thermal‐runaway‐motivated combustion failure mechanism for one of the PVB formulations and identified densification, cracking, and haze‐formation behaviors in some of the silicone specimens. The behaviors observed for the silicone specimens may be facilitated by their greater thickness. Copyright © 2012 John Wiley & Sons, Ltd.

A fiber-based single-unit dual-mode optical Imaging system: Swept source optical coherence tomography and fluorescence spectroscopy

We propose a fiber optic single-unit but dual-mode optical imaging system that can provide fast cross-sectional imaging capabilities of swept-source optical coherence tomography (SS-OCT) and functional capabilities of fluorescence spectroscopy (FS). By adopting a fiber optic FS system into a fiber-based SS-OCT system, a compact and effective multimodal single-unit SSOCT-FS system is achieved. Here, the key element of the proposed multimodal imaging system is a specially designed fiber coupler based on double-clad fiber (DCF), which has only cladding-mode coupling capability. The DCF couplers are fabricated with home-drawn DCF by several fabrication methods; a twisting method, a side-polishing method and a fused biconical tapered (FBT) method. Experimentally, the FBT method provides rather flat cladding mode coupling efficiency over 40% in a wide wavelength range. With this specially designed DCF coupler, the OCT signal and the fluorescence signal is measured independently but with a single-unit system. The performance of the SSOCT-FS system is confirmed by measuring the cross-sectional image and the fluorescence signal of a photosensitizer chlorin e6 injected in-vivo rat tumor model.

The Use of Piers–Rubinsztajn Conditions for the Placement of Triarylamines Pendant to Silicone Polymers

The use of Piers–Rubinsztajn conditions was explored for the synthesis of silicone polymers bearing pendant triarylamine functionality. We have found that up to 60% of the hydride groups of a silicone copolymer can be successfully substituted with a triarylamine moiety, without metathesis or redistribution of the silicone. The resulting polymers are hydrolytically stable. The functionalization procedure is straightforward, conducted under ambient conditions with a simple one-step work-up, and avoids the use of a metal-based catalyst. The resulting phenylated triarylamine–silicone hybrid polymer was characterized by optical absorption and fluorescence spectroscopy, CV, and differential scanning calorimetry. The hybrids maintain the physical appearance of a silicone polymer while adopting the photophysical and electrochemical characteristics of the triarylamine.

Blue Fluorescent Liquid Crystal N-(4-methoxybenzylidene)-4-n-alkoxybenzenamine

Rod-like liquid crystals N-(4-methoxybenzylidene)-4-n-alkoxybenzenamine (MBnBA,n= 1, 2, 10) were synthesized and then were investigated by differential scanning calorimetry, polarizing optical microscopy, ultraviolet-visible spectrophotometry and fluorescence spectroscopy. Our results demonstrated that the dilute tetrahydrofuran solutions of each member in the family of MBnBA could give off blue fluorescence under the 325 nm excitation. The calculated electronic structures revealed that the fluorescence recorded at 469 nm (2.65 eV) was the result ofπ* →ntransitions in the molecules of the synthesized liquid crystals MBnBA.

Stabilization of tetragonal phase in ZrO 2:Eu by rapid thermal heating

Europium-doped Zr(OH) 4 nanoparticles are heated via furnace and pyroprobe. As observed in X-ray diffraction and optical fluorescence spectroscopy, both heating techniques lead to mixed tetragonal and monoclinic crystalline ZrO 2 phases. Three hours of heating in the furnace leads to 45% tetragonal phase at 400 °C and only 14% at 700 °C. Rapid 10 s heating in the pyroprobe, however, leads up to 68% tetragonal phase for temperatures between 570 and 710 °C. Incomplete dehydroxylation of the precursor may lead to the stabilization of the tetragonal phase.

Photo-dynamics of the BLUF domain containing soluble adenylate cyclase (nPAC) from the amoeboflagellate Naegleria gruberi NEG-M strain

The amoeboflagellate Naegleria gruberi NEG-M comprises a BLUF ( blue light sensor using flavin) regulated adenylate cyclase (nPAC). The nPAC gene was expressed heterologously in Escherichia coli and the photo-dynamics of the nPAC protein was studied by optical absorption and fluorescence spectroscopy. Blue-light exposure of nPAC caused a typical BLUF-type photo-cycle behavior (spectral absorption red-shift, fluorescence quenching, absorption and fluorescence recovery in the dark). Additionally, time-delayed reversible photo-induced one-electron reduction of fully oxidized flavin (Fl ox) to semi-reduced flavin (FlH ) occurred. Furthermore, photo-excitation of FlH caused irreversible electron transfer to fully reduced anionic flavin (FlH −). A photo-induced electron transfer from Tyr or Trp to flavin (Tyr + –Fl − or Trp + –Fl − radical ion-pair formation) is thought to cause H-bond restructuring responsible for BLUF-type photo-cycling and permanent protein re-conformation enabling photo-induced flavin reduction by proton transfer. Some photo-degradation of Fl ox to lumichrome was observed. A model of the photo-dynamics of nPAC is developed.

Early stage aggregation of human serum albumin in the presence of metal ions

The heat induced aggregation of human serum albumin (HSA) with and without an equimolar amount of Cu(II) and Zn(II) was investigated by using optical absorption, fluorescence, AFM and EPR spectroscopy. Turbidity experiments as a function of temperature indicate that the protein aggregation occurs after the melting of the protein. The kinetic of HSA aggregation, investigated between 60 and 70°C by monitoring the optical density changes at 400nm on a 180min time window, shows an exponential growth with a rate that increases with the temperature. Fluorescence of the thioflavin T evidences a significant increase of the intensity at 480nm at increasing incubation time. These results combined with AFM experiments show that the protein aggregates are elongated oligomers with fibrillar-like features. The absence of a lag-phase suggests that the early stage aggregation of HSA follows a downhill pathway that does not require the formation of an organized nucleus. The presence of Cu(II) and Zn(II) ions does not affect the thermally induced aggregation process and the morphology of HSA aggregates. The result is compatible with the binding of the metal ions to the protein in the native state and with the high conformational stability of HSA.

Multimodal analysis of pearls and pearl treatments by using optical coherence tomography and fluorescence spectroscopy

We present an integrated optical system that consists of optical coherence tomography (OCT) and laser-induced fluorescence (LIF) spectroscopy for multimodal analysis of pearls and pearl treatments. The OCT source and the LIF excitation beams were aligned together to illuminate the same spot of a pearl fixed on the sample stage that was under rotation. As a result, both OCT images and LIF spectra of the pearls were detected at the same time and also at the same place. For OCT, a 1310 nm-centered swept laser source was used. For LIF, a 405 nm laser diode was used and a lensed multimode fiber was utilized as a fluorescence probe. The tomographic investigation on the internal structure of a pearl allowed us to evaluate and categorize the pearl nondestructively as was previously reported. In addition, the measurements of fluorescence spectrum and its decaying rate helped to determine the species of mother oyster. The proposed multimodal analysis made it possible to classify the pearls and also to disclose the treatments made on the pearls.

Specialty Fiber Coupler: Fabrications and Applications

We review the research on specialty fiber couplers with emphasis placed on the characteristics that make them attractive for biomedical imaging, optical communications, and sensing applications. The fabrication of fiber couplers has been carried out with, in addition to conventional single mode fiber, various specialty fibers such as photonic crystal fiber, double clad fiber, and hole-assisted fiber with a Ge-doped core. For the fiber coupler fabrication, the side polishing and the fused biconical tapered methods have been developed. These specialty fiber couplers have been applied to optical coherence tomography, fluorescence spectroscopy, fiber sensors, and optical communication systems. This review aims to provide a detailed statement on the recent progress and novel applications of specialty fiber couplers.

Comparative study of non-destructive methods to quantify thickness of tablet coatings

The Supercell coater is a newly introduced coater which utilizes air fluidization for tablet coating. The aim of this study was to define a suitable, fast and non-destructive method for the quantification of coat thickness for Supercell-coated tablets. Various coat thickness characterization methods were carried out on tablets coated at different process conditions. These include the use of optical microscopy, micrometer, X-ray fluorescence (XRF), Raman and near-infrared (NIR) spectroscopy. Coat thicknesses obtained from direct measurements were used to calibrate the spectral data from spectroscopic methods for model generation. The models were subsequently validated to evaluate their prediction capabilities, especially the ability to differentiate tablets coated at different conditions. XRF spectroscopy was viewed to be more suitable for the assessment of process yield and efficiency but both Raman and NIR spectroscopy were shown to be more appropriate methods for the rapid prediction and evaluation of coat thickness. However, only Raman spectroscopy was able to differentiate tablets coated under different conditions accurately. In conclusion, direct thickness measurements were more time-consuming but provided assured coat thickness data. On the other hand, XRF, Raman and NIR spectroscopy methods were viable alternatives to provide complementary information for the study of tablet coatings.

Phenanthrene Crystals Fluorescence Under High-Pressure and Shear

Investigations of crystalline phenanthrene in the Bridgman diamond anvils under pressure up to 5,0 GPa and simultaneous shear caused by optical microscopy and fluorescence spectroscopy were carried out. It’s proven that phenanthrene fluorescence spectrums are reversibly changed under high pressure. The phenanthrene vibrational structure of lines disappears similar to the one of the anthracene. Dimerization or any other irreversible changes under combination of high pressure and shear in phenanthrene, unlike anthracene, were not observed.

The Development of Double Clad Fiber and Double Clad Fiber Coupler for Fiber Based Biomedical Imaging Systems

We report the fabrication of double clad fiber (DCF) and DCF coupler, suitable for fiber based imaging systems requiring the dual-channel transmission. Unlike the conventional DCF which uses silica for both cladding layers, the proposed DCF uses a low-index polymer for its outer-cladding layer coated over the conventional silica inner-cladding layer. The DCF is drawn with a conventional SMF preform but a low-index polymer coating is used for both jacket and outercladding of the fiber. To achieve the cladding mode coupling, a DCF coupler is fabricated by simply twisting two pieces of the proposed DCF after removing the polymer-coating at contacting regions. A cladding mode coupling ratio of 30% was achieved with a contact length of 16 cm. The proposed DCF and DCF coupler were employed in a composite optical coherence tomography (OCT) and fluorescence spectroscopy (FS) system, and both OCT images and FS signal from a plant tissue are measured simultaneously.

Design and Evaluation of a Passive Alcove-Based Microfluidic Mixer

A novel passive microfluidic silicon mixer has been designed, optimized and fabricated. The architecture of the mixer consists of a simple "T" junction, made up by a 20 microm wide by 82 microm deep channel, followed by three repeats of an alcove, each with a triangular obstruction, arranged in a zigzag fashion. Numerical simulations were employed to optimize the geometry, particularly the dimensions of the alcoves, the relative orientation and the spacing between them, and the degree of intrusion associated with them. The simulation results demonstrate that chaotic flow due to recirculation within the alcoves results in transverse velocity that promotes effective fluid mixing. The microfluidic mixer with the simulation-optimized geometry was fabricated with photolithographic techniques and characterized by optical imaging, fluorescence, and Raman microscope spectroscopy. At a sample flow rate of 20 microL/s, the mixer exhibits a short mixing deadtime of approximately 22 micros and a high mixing efficiency under both low and high viscosity conditions. The alcove-based microfluidic silicon mixer offers unique advantages for its short deadtime and slow sample consumption rate. In addition, it provides a valuable component for laboratory-on-a-chip applications for its ease of development into multiple networks for massively parallel analytical processes.

In-vivo optical detection of cancer using chlorin e6 – polyvinylpyrrolidone induced fluorescence imaging and spectroscopy

BackgroundPhotosensitizer based fluorescence imaging and spectroscopy is fast becoming a promising approach for cancer detection. The purpose of this study was to examine the use of the photosensitizer chlorin e6 (Ce6) formulated in polyvinylpyrrolidone (PVP) as a potential exogenous fluorophore for fluorescence imaging and spectroscopic detection of human cancer tissue xenografted in preclinical models as well as in a patient.MethodsFluorescence imaging was performed on MGH human bladder tumor xenografted on both the chick chorioallantoic membrane (CAM) and the murine model using a fluorescence endoscopy imaging system. In addition, fiber optic based fluorescence spectroscopy was performed on tumors and various normal organs in the same mice to validate the macroscopic images. In one patient, fluorescence imaging was performed on angiosarcoma lesions and normal skin in conjunction with fluorescence spectroscopy to validate Ce6-PVP induced fluorescence visual assessment of the lesions.ResultsMargins of tumor xenografts in the CAM model were clearly outlined under fluorescence imaging. Ce6-PVP-induced fluorescence imaging yielded a specificity of 83% on the CAM model. In mice, fluorescence intensity of Ce6-PVP was higher in bladder tumor compared to adjacent muscle and normal bladder. Clinical results confirmed that fluorescence imaging clearly captured the fluorescence of Ce6-PVP in angiosarcoma lesions and good correlation was found between fluorescence imaging and spectral measurement in the patient.ConclusionCombination of Ce6-PVP induced fluorescence imaging and spectroscopy could allow for optical detection and discrimination between cancer and the surrounding normal tissues. Ce6-PVP seems to be a promising fluorophore for fluorescence diagnosis of cancer.

Photo-dynamics of roseoflavin and riboflavin in aqueous and organic solvents

Roseoflavin (8-dimethylamino-8-demethyl- d-riboflavin) and riboflavin in aqueous and organic solvents are studied by optical absorption spectroscopy, fluorescence spectroscopy, and fluorescence decay kinetics. Solvent polarity dependent absorption shifts are observed. The fluorescence quantum yields are solvent dependent. For roseoflavin the fluorescence decay shows a bi-exponential dependence (ps to sub-ps time constant, and 100 ps to a few ns time constant). The roseoflavin photo-dynamics is explained in terms of fast intra-molecular charge transfer (diabatic electron transfer) from the dimethylamino electron donor group to the pteridin carbonyl electron acceptor followed by intra-molecular charge recombination. The fast fluorescence component is due to direct locally-excited-state emission, and the slow fluorescence component is due to delayed locally-excited-state emission and charge transfer state emission. The fluorescence decay of riboflavin is mono-exponential. The S 1-state potential energy surface is determined by vibronic relaxation and solvation dynamics due to excited-state dipole moment changes (adiabatic optical electron transfer).

The importance of the photonic mode density in bioassays based on evanescent optical waves

We have determined limits of detection (LODs) of DNA hybridization using an optical detection by two different method, i.e., surface plasmon fluorescence spectroscopy (SPFS) and optical waveguide fluorescence spectroscopy (OWFS), however, an identical sensor. Both techniques have a similar detection principle using the enhanced electromagnetic field to excite fluorophores and to monitor DNA hybridization in real-time with high sensitivity. Firstly, the detection of DNA hybridization was conducted by SPFS and the LOD value was found to be 2.0pM (2.0×10−12mol∕L). The same study was further conducted by OWFS, and a LOD of 170fM (1.7×10−13mol∕L) and 100fM (1×10−13mol∕L) was achieved for TM1 and TE0 modes, respectively, indicating that an improvement of the LOD of one order of magnitude is possible with OWFS. Furthermore, the photonic mode density at resonance of each mode was calculated, and these values are reflected in the LOD values. The present study illustrates the potential of OWFS as biosensor applications being able to detect in real-time even trace amounts of analyte.

Effects of molecular orientation of fluorescently-labeled duplex DNA on emission anisotropy

The molecular orientation of Cy5-labeled target DNA hybridized on a probe DNA layer was studied on a planar waveguide in the Kretchmann configuration at various target DNA bulk concentration. Optical waveguide fluorescence spectroscopy (OWFS) was employed to evaluate the fluorescence emission anisotropy by analyzing two polarized modes, i.e., TM and TE modes propagating in a waveguide. In this way, the orientational order parameter S could be determined. It was found that the orientation of DNA duplex molecules is disordered at lower concentrations, while relatively ordered at higher concentrations.

Combined system of optical coherence tomography and fluorescence spectroscopy based on double-cladding fiber

We report the development of an all-fiber multimodal system, based on a double-cladding fiber (DCF) and related devices, suitable for simultaneous measurements of optical coherence tomography (OCT) and fluorescence spectroscopy (FS). The DCF together with a DCF coupler and a single-body DCF lens has assisted in the realization of a multimodal but single-unit probe for the combined system. The DCF lens allowed simultaneous focusing of input beams for OCT and FS and also the effective collection of both signal beams from a sample. The DCF coupler could extract the OCT signal via the core channel and the FS signal through the cladding channel. The OCT image and the fluorescence spectra of a plant tissue were then simultaneously measured to validate the performance of the proposed multimodal system.

Comparison of the Quality of Aqueous Dispersions of Single Wall Carbon Nanotubes Using Surfactants and Biomolecules

The use of single wall carbon nanotubes (SWCNTs) in current and future applications depends on the ability to process SWCNTs in a solvent to yield high-quality dispersions characterized by individual SWCNTs and possessing a minimum of SWCNT bundles. Many approaches for the dispersion of SWCNTs have been reported. However, there is no general assessment which compares the relative quality and dispersion efficiency of the respective methods. Herein we report a quantitative comparison of the relative ability of "wrapping polymers" including oligonucleotides, peptides, lignin, chitosan, and cellulose and surfactants such as cholates, ionic liquids, and organosulfates to disperse SWCNTs in water. Optical absorption and fluorescence spectroscopy provide quantitative characterization (amount of SWCNTs that can be suspended by a given surfactant and its ability to debundle SWCNTs) of these suspensions. Sodium deoxy cholate (SDOCO), oligonucleotides (GT)(15), (GT)(10), (AC)(15), (AC)(10), C(10-30), and carboxymethylcellulose (CBMC-250K) exhibited the highest quality suspensions of the various systems studied in this work. The information presented here provides a good framework for further study of SWCNT purification and applications.