Characteristic Fluorescence Spectra Research Articles

A sensitive resveratrol assay with a simple probe methylene blue by resonance light scattering technique

A novel resonance light scattering (RLS) method was developed for the determination of resveratrol based on the interaction between resveratrol and methylene blue (MB). It was found that at pH 8.69, the weak RLS intensity of MB was remarkably enhanced by the addition of trace amount of resveratrol with the maximum peak located at 385.0 nm. Under the optimum conditions, a good linear relationship between the enhanced RLS intensities and the concentrations of resveratrol was obtained over the range of 2.0–14.0 μg ml −1 with the detection limit (3 σ) of 0.63 μg ml −1. The results of the analysis of resveratrol in synthetic samples and human urine are satisfactory, which showed it may provide a more sensitive, convenient, rapid and reproducible method for the detection of resveratrol, especially in biological and pharmaceutical field. In this work, the characteristics of RLS, absorption and fluorescence spectra of the resveratrol–MB system, the influencing factors and the optimum conditions of the reaction were investigated.

Pollution of Musts and Wines: A New Method for the Determination of Petroleum By-Products Using Fluorescence

Pollution of musts and wines by petroleum by-products may happen accidentally by mechanical machines, particularly during harvests. A new method for detecting and determining this type of pollutant, using fluorescence, has been developed in the present work. The principal pollutant investigated was diesel fuel which exhibits a characteristic fluorescence spectrum, whichever its origin. Fluorescence is principally emitted by traces of polycyclic aromatic compounds (PACs), principally polycyclic aromatic hydrocarbons (PAHs), contained in most petroleum by-products. The method involves a liquid-liquid extraction of PAHs using cyclohexane and fluorescence measurements were performed on the resulting “cyclohexane extracts.” Some natural compounds extracted from must and wine samples may also exhibit an intrinsic fluorescence emission which interferes with the characteristic fluorescence of pollutants. This is the case, in particular, of tannins contained in red wines and in wood. Thus, this prevents any reliable determination of pollutants. Natural compounds were efficiently separated from PAHs using solid phase extraction by elution of the cyclohexane solution on the florisil phase. The corresponding fluorescence was totally eliminated at the characteristic emission wavelength of pollutants. Thus, the presence of any pollution by diesel fuel could be characterized unambiguously and determined accurately. The limits of detection and quantification were determined to be around 0.3 and 1.0 μL L−1, respectively. Uncertainties on determinations were estimated at less than 20% for diesel fuel, provided a reference spectrum of the pollutant is available. If not, the pollutant concentration can be estimated within a factor two. The evolution of the pollution with time was also investigated over several weeks, particularly during the time of fermentation. The method is fairly simple to implement, quick and reliable.

Study on the interaction between hematoporphyrin monomethyl ether and DNA and the determination of hematoporphyrin monomethyl ether using the resonance light scattering technique

The interaction between photosensitizer anticancer drug hematoporphyrin monomethyl ether (HMME) and ctDNA has been studied based on the decreased resonance light scattering (RLS) phenomenon. The RLS, UV–vis and fluorescence spectra characteristics of the HMME–ctDNA system were investigated. Besides, the phosphodiesters quaternary ammonium salt (PQAS), a kind of new gemini surfactant synthesized recently, was used to determine anticancer drug HMME based on the increasing RLS intensity. Under the optimum assay conditions, the enhanced RLS intensity was proportional to the concentration of HMME. The linear range was 0.8–8.4 μg mL −1, with correlation coefficient R 2 = 0.9913. The detection limit was 0.014 μg mL −1. The human serum samples and urine samples were determined satisfactorily, which proved that this method was reliable and applicable in the determination of HMME in body fluid. The presented method was simple, sensitive and straightforward and could be a significant method in clinical analysis.

Characterization of eight different tetracyclines: advances in fluorescence bone labeling

Polychrome sequential labeling with fluorochromes is a standard technique for the investigation of bone formation and regeneration processes in vivo. However, for human application, only tetracycline and its derivates are approved as fluorochromes. Therefore, the aim of this study was to determine the fluorescence characteristics of the different tetracycline derivates to assess the feasibility of sequential in vivo bone labeling using distinguishable fluorochromes. Eight different tetracycline derivates were injected subcutaneously into growing rats as a single dose or sequentially in different combinations. After preparation of resin-embedded undecalcified bone sections, the fluorescence properties of the tetracycline derivates in bone were analyzed using conventional fluorescence microscopy, spectral image analysis and confocal laser scanning microscopy. Each tetracycline derivate exhibited a characteristic fluorescence spectrum, but the differences between them were small. Chlortetracycline could be discriminated reliably from all other derivates and could therefore be combined with any other tetracycline derivate for reliably distinguishable double labeling. Tetracycline itself exhibited the brightest fluorescence of all the investigated derivates. Interestingly, in conventional microscopy the same tetracycline derivative can appear in different colours to the human eye, even if spectral analysis confirmed identical emission peaks. In conclusion, the data suggest that fluorescence double labeling of bone is feasible using appropriate tetracycline derivates in combination with spectral imaging modalities.

Supramolecular complexes of tetrapyrrolic macrocycles: A basis for developing new molecular technologies

Developing new effective means for the real-time detection of chemical and biochemical species by using sensors is one of the most significant problems in modern science. The physicochemical properties of the sensing agent used to generate the diagnostic signal are central to determining the overall performance of a chemical sensor. By choosing one or another agent, it is possible to vary the sensor selectivity, endurance, and response time in the presence of the analyzed compound in the medium. The way the initial chemical signal is transformed into an analytical one that can be directly used for a subsequent analysis is also of great importance, because it largely determines the ease of production and exploitation of the sensing device. Representatives of the tetrapyrrolic family have characteristic absorption and fluorescence spectra that can be used to transform the initial diagnostic response into an optical sensor signal. Along with this, these compounds can be also used as a source of the initial analytical signal because they are able to interact with a number of low molecular substances forming molecular complexes. This article reviews current approaches for producing supramolecular receptors based on tetrapyrrolic compounds and analyzes the prospects for their further application in the development of new molecular technologies such as luminescence molecular detectors, pH-switches, gas sensors, etc.

Filamentation “remote” sensing of chemical and biological agents/pollutants using only one femtosecond laser source

All matters in the path of filaments induced by an intense femtosecond laser pulse propagating in air could be fragmented and result in the emission of characteristic fluorescence spectra from the excited fragments. The fluorescence spectra exhibit specific signatures (fingerprints) that can be used for the identification of various substances including chemical and biological species. In this paper, we present an overview of the recent progress in our laboratory concerning the “remote” sensing of chemical and biological agents/pollutants in air using filamentation-induced nonlinear fluorescence techniques.

Parametric Investigation of Laser-Induced Fluorescence of Solid-State Uranyl Compounds

The combination of remote/standoff sensing and laser-induced fluorescence (LIF) spectroscopy shows potential for detection of uranyl (UO2(2+)) compounds. Uranyl compounds exhibit characteristic emission in the 450-600 nm (22,200 to 16,700 cm(-1)) spectral region when excited by wavelengths in the ultraviolet or in the short-wavelength portion of the visible spectrum. We report a parametric study of the effects of excitation wavelength [including 532 nm (18,797 cm(-1)), 355 nm (28,169 cm(-1)), and 266 nm (37,594 cm(-1))] and excitation laser power on solid-state uranium compounds. The uranium compounds investigated include uranyl nitrate, uranyl sulfate, uranyl oxalate, uranium dioxide, triuranium octaoxide, uranyl acetate, uranyl formate, zinc uranyl acetate, and uranyl phosphate. We observed the characteristic uranyl fluorescence spectrum from the uranium compounds except for uranium oxide compounds (which do not contain the uranyl moiety) and for uranyl formate, which has a low fluorescence quantum yield. Relative uranyl fluorescence intensity is greatest for 355 nm excitation, and the order of decreasing fluorescence intensity with excitation wavelength (relative intensity/laser output) is 355 nm > 266 nm > 532 nm. For 532 nm excitation, the emission spectrum is produced by two-photon excitation. Uranyl fluorescence intensity increases linearly with increasing laser power, but the rate of fluorescence intensity increase is different for different emission bands.

Mechanisms of Ligand Transfer by the Hepatic Tocopherol Transfer Protein

alpha-Tocopherol is a member of the vitamin E family that functions as the principal fat-soluble antioxidant in vertebrates. Body-wide distribution of tocopherol is regulated by the hepatic alpha-tocopherol transfer protein (alphaTTP), which stimulates secretion of the vitamin from hepatocytes to circulating lipoproteins. This biological activity of alphaTTP is thought to stem from its ability to facilitate the transfer of vitamin E between membranes, but the mechanism by which the protein exerts this activity remains poorly understood. Using a fluorescence energy transfer methodology, we found that the rate of tocopherol transfer from lipid vesicles to alphaTTP increases with increasing alphaTTP concentration. This concentration dependence indicates that ligand transfer by alphaTTP involves direct protein-membrane interaction. In support of this notion, equilibrium analyses employing filtration, dual polarization interferometry, and tryptophan fluorescence demonstrated the presence of a stable alphaTTP-bilayer complex. The physical association of alphaTTP with membranes is markedly sensitive to the presence of vitamin E in the bilayer. Some naturally occurring mutations in alphaTTP that cause the hereditary disorder ataxia with vitamin E deficiency diminish the effect of tocopherol on the protein-membrane association, suggesting a possible mechanism for the accompanying pathology.

Spectroscopic determination of solvation shell composition of fluorenone and 4-hydroxyfluorenone in binary solvent mixtures

Preferential solvation of fluorenone (9Fl) and 4-hydroxyfluorenone (4HOFl) in binary solvent mixtures (cyclohexane–tetrahydrofuran (CH–THF) and cyclohexane–ethanol (CH–EtOH)) has been studied using steady-state spectroscopic measurements. The solvation of the fluorenones, both in the ground and in the excited states, exhibits a non-linear solvatochromic shifts as a function of polar component in the binary solvent mixtures. The results of spectroscopic measurements were used to calculate, according to Bakhshiev's and Kiselev's theory, the fluorescence spectra of solvates having different number of polar component in the first solvation shell. The different features of fluorescence spectra of molecule under study in CH–THF and CH–EtOH are explained by the absence and presence of specific solute–solvent interactions (hydrogen bond).

Estimation of relative contribution of “mobile phycobilisome” and “energy spillover” in the light–dark induced state transition in Spirulina platensis

Previously, it was clarified that phycobilisome (PBS) mobility and energy spillover were both involved in light-to-dark induced state transitions of intact Spirulina platensis cells. In this work, by taking advantage of the characteristic fluorescence spectra of photosystem I (PSI) trimers and monomers as indicators, the relative contributions for the "mobile PBS" and "energy spillover" are quantitatively estimated by separating the fluorescence contribution of PBS mobility from that of PSI oligomeric change. Above the phase transition temperature (TPT) of the membrane lipids, the relative proportion of the contributions is invariable with 65% of "mobile PBS" and 35% of "energy spillover". Below TPT, the proportion for the "mobile PBS" becomes larger under lowering temperature even reaching 95% with 5% "energy spillover" at 0 degrees C. It is known that lower temperature leads to a further light state due to a more reduced or oxidized PQ pool. Based on the current result, it can be deduced that disequilibrium of the redox state of the PQ pool will trigger PBS movement instead of change in the PSI oligomeric state.

Identification of Fluorescent U(V) and U(VI) Microparticles in a Multispecies Biofilm by Confocal Laser Scanning Microscopy and Fluorescence Spectroscopy

Fluorescent uranium(V) and uranium(VI) particles were observed for the first time in vivo by a combined laser fluorescence spectroscopy and confocal laser scanning microscopy approach in a living multispecies biofilm grown on biotite plates. These particles ranged between 1 and 7 um in width and up to 20 microm in length and were located at the bottom and at the edges of biofilms colonies. Analysis of amplified 16S rRNA fragments and fluorescence in situ hybridization were used to characterize the biofilm communities. Laser fluorescence spectroscopy was used to identify these particles. The particles showed either a characteristic fluorescence spectrum in the wavelength range of 415-475 nm, indicative for uranium(V), or in the range of 480-560 nm, which is typical for uranium(VI). Particles of uranium(V) as well as uranium(VI) were simultaneously observed in the biofilms. These uranium particles were attributed for uranium(VI) to biologically mediated precipitation and for uranium(V) to redox processes taking place within the biofilm. The detection of uranium(V) in a multispecies biofilm was interpreted as a short-lived intermediate of the uranium(VI) to uranium(IV) redox reaction. Its presence clearly documents that the uranium(VI) reduction is not a two electron step but that only one electron is involved.

Study of 660 nm laser-induced photoluminescence of chlorophyll-a and its applications

Based on the phenomenon of chlorophyll a photoluminescence, this paper introduces a new method to measure the chlorophyll a content, using 660nm laser diode as a new kind of light source to stimulate fluorescence as well as combining a fiber and spectrum technique. We analyze the characteristics of laser-induced fluorescence spectrum of chlorophyll a and then put forward the new method using two parameters, the relative fluorescence intensity and fluorescence intensity ratio F685/F735, to measure the chlorophyll a content in the water and green leaves respectively. The experimental results indicate that it is completely feasible to give a visual judgment for chlorophyll a content, according to the fluorescence emission spectrum of chlorophyll a. Subsequently, it is verified by three kinds of typical applications. All of these provide a new kind of light source to develop the chlorophyll a fluorometry and further give a technical foundation of on-spot monitoring the chlorophyll a content in the ocean or in green leaves.

Fluorescence spectrum characteristic of ethanol–water excimer and mechanism of resonance energy transfer

The steady-state fluorescence spectrum characteristic of ethanol–water excimer has been studied in this paper. By analysing the features of the sharp emission spectrum with fine structures in a shortwave band and the characteristics of the broad and featureless fluorescence peaks in the longwave band, one can conclude that the excimers are formed between the new ethanol–water cluster molecules in the excited state and the ground state through the interaction among different chromophores. The excitation spectra in the two fluorescence bands have been studied, and their emission mechanisms have been ascertained based on the energy transfer theory. Furthermore, the critical distance of the resonance energy transfer has been calculated.

Features of fluorescence spectra of polyethylene 2,6‐naphthalate films

AbstractThe characteristics of the fluorescence spectra of polyethylene 2,6‐naphthalate (PEN) films were compared with those of poly(ethylene terephthalate) (PET). The fluorescence spectra of PEN films were found, by photoselection, to consist of two components, one peaking at 425 nm and the other at 445 nm, with their emission transition moments perpendicular to each other. The integrated excitation spectra of the PEN films were much more intense than those of PET. After the resolution of the integrated excitation spectra of PEN, most, but not all, of their component peaks corresponded to those of the absorption spectra. On the basis of this fact together with previous data on photodegradation, the spectral component peaking at 445 nm originated, at least partly, from traces of photochemical products generated by exposure during the measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 114–121, 2007

Multifactor analysis in laser fluorescence diagnostics

Fluorescence spectra induced by a He-Ne laser in a complex biological medium (blood plasma) are studied. The statistical analysis of the spectra reveals regular correlations between the spectral parameters and concentration of substances known as porphyrinic pigments. The common factors of the spectral characteristics of fluorescence spectra are chosen as the diagnostic parameters. A model for differential diagnostics based on factor analysis is proposed.

Growth and Optical Spectra of Zn:Er:LiNbO 3 Crystals Using Bridgman Method

The growth of LiNbO 3 single crystal with Er 3+ and Zn 2+ co-doped using Bridgman method and its characteristic absorption spectra and fluorescence spectra were reported. Large-size crystals initially containing Zn 2+ (3%) and Er 3+ (0.6%) with good optical quality were obtained using optimized conditions such as a growth rate of 0.8 ∼ 1.5 mm·h −1 and a temperature gradient of about 30 ∼ 35 °C · cm −1 across the solid-liquid interface and the sealed platinum crucible. X-ray diffraction and differential thermal analysis (DTA) were used to characterize the crystals. The results indicate that the concentration of Er 3+ ions in crystals, their absorption intensity, and their fluorescence intensity decrease from the bottom to the top in the crystals. However, for the upper part of the crystal, the up-conversion fluorescence intensity is higher than that of the lower part excited by an 800 or 970 nm pump. The effects of the crystal lattice, their structural defect and their effective segregation of Er 3+ ions were discussed with respect to the variations of the up-conversion fluorescence intensity.

Variable phase-contrast fluorescence spectrometry for fluorescently stained cells

This letter describes the spectroscopic measurements of fluorescently stained cells. Variable phase-contrast fluorescence spectrometry was used on fluorescently stained cells to achieve high two-dimensional spatial resolution. Phase shift interferometry by autocorrelation interference made it possible to measure fluorescence spectra in the field of view without the separation of wavelengths, as in the case of a conventional dispersive spectrometer. In this letter, the authors describe the experimental characteristics of fluorescence spectra generated from fluorescently stained cells and verify that the fluorescence spectra of the stained area in the cells can be measured by our method.

Study on the Interactions of Ruthenium(III), Rhodium(III) and Palladium(II) Ions with DNA

Fluorescence, absorption and circular dichroism spectra have been used in the interactions of ruthenium(III), rhodium(III) and palladium(II) ions with DNA with berberine as a probe (berberine, Scheme 1). The results are as follows: ruthenium(III) and rhodium(III) ions show different effects from that of the palladium(II) ion on the fluorescence spectra characteristics of berberine-DNA system. Quenching fluorescence is seen with palladium(II) ion addition, whereas increasing fluorescence is observed for ruthenium(III) and rhodium(III) ions. The addition of ruthenium(III), rhodium(III) and palladium(II) ions causes the increasing absorption of the DNA solution. The addition of ruthenium(III), rhodium(III) and palladium(II) ions to the DNA solution also causes the circular dichroism spectra to change. The above results suggest that different metal ions exhibit different affinity when binding to DNA, which could correlate well with the ions’ charge, structure and the ability to coordinate. There is a comparison between Pt(IV) and Pd(II) ions on the fluorescence of the berberine-DNA system.

Native Fluorescence of Oral Cavity Structures: An Experimental Study in Dogs

The aim of this study was to compare the fluorescence of different areas of the buccal mucosa of dogs. Native fluorescence occurs in many animal and plant tissues following excitation by ultraviolet (UV) light. The fluorescence spectrum characteristic of a given tissue may vary with changes in tissue composition and organization. Hence, this optical phenomenon provides a reliable and minimally invasive diagnostic tool for examining tissues in normal and pathological conditions. The oral cavity contains a variety of structures, including the lips, tongue, palate, and gingiva that differ in their location and function. These structures can be easily traumatized or display different degrees of keratinization. The study sample was 20 healthy, adult, mongrel dogs of both sexes. The dogs were anesthetized and manipulated in compliance with institutional guidelines. The fluorescence spectra were obtained using a "plug-in" spectrometer and optical fibers, with a final resolution better than 2 nm. The fluorescence of seven different areas (floor of the mouth, palate, gingiva, dorsal and ventral surface of tongue, buccal mucosa, and teeth) was examined. A UVHg lamp (emission wavelength, 350-410 nm) was used for excitation. One hundred and forty spectra were collected from various regions of the oral cavity, and all of them showed similar profiles, with maximum fluorescence of 500-520 nm. The similarity of the spectra for the different sites allowed us to establish a standard fluorescence spectrum of the buccal cavity.

Surface elemental analysis in ambient atmosphere using electron-induced x-ray fluorescence

The progress in the development of the atmospheric electron x-ray spectrometer (AEXS) is described. The AEXS is a surface analysis tool based on excitation of characteristic x-ray fluorescence (XRF) spectra from samples in ambient atmospheres using a focused electron beam. Operation in ambient atmospheres with moderate-to-high spatial resolution in comparison to similar instruments is obtained through the use of a thin electron-transmissive membrane to isolate the vacuum of the electron probe, obviating the need for the samples to be drawn into the probe vacuum. Our initial setup that was used for the demonstration of the ability of the transmitted electrons to excite the XRF spectra in the external atmosphere consisted of an actively pumped chamber from within which the electrons were transmitted—not a portable instrument. The AEXS instrument that has been assembled in our laboratory during the past year consists of a miniature 20 keV electron microprobe that is vacuum sealed with a thin SiN membrane and...