Energy transfer mechanism of PBS-thylakoid complexes——By time-resolved fluorescence spectra technique

IN a previous paper, we have studied the energy transfer mechanism among the PBS-thy-lakoid complex in detail by using steady-state spectra and deconvolution techniques. The ex-perimental results indicated that the energy transfer from PBS to two reaction centers of PS Ⅰand PS Ⅱ were parallel, and confirmed the model which was suggested by Mullineaxu.

Time-resolved characteristics of a nanosecond pulsed multi-hollow needle plate packed bed dielectric barrier discharge

In this paper,self-designed multi-hollow needle electrodes are used as a high-voltage electrode in a packed bed dielectric barrier discharge reactor to facilitate fast gas flow through the active discharge area and achieve large-volume stable discharge.The dynamic characteristics of the plasma,the generated active species,and the energy transfer mechanisms in both positive discharge(PD)and negative discharge(ND)are investigated by using fast-exposure intensified charge coupled device(ICCD)images and time-resolved optical emission spectra.The experimental results show that the discharge intensity,number of discharge channels,and discharge volume are obviously enhanced when the multi-needle electrode is replaced by a multihollow needle electrode.During a single voltage pulse period,PD mainly develops in a streamer mode,which results in a stronger discharge current,luminous intensity,and E/N compared with the diffuse mode observed in ND.In PD,as the gap between dielectric beads changes from 0 to250μm,the discharge between the dielectric bead gap changes from a partial discharge to a standing filamentary micro-discharge,which allows the plasma to leave the local area and is conducive to the propagation of surface streamers.In ND,the discharge only appears as a diffusionlike mode between the gap of dielectric beads,regardless of whether there is a discharge gap.Moreover,the generation of excited states N_(2)^(+)(B^(2)∑_(u)^(+))and N2(C^(3)Π_(u))is mainly observed in PD,which is attributed to the higher E/N in PD than that in ND.However,the generation of the OH(A^(2)∑^(+))radical in ND is higher than in PD.It is not directly dominated by E/N,but mainly by the resonant energy transfer process between metastable N_(2)(A^(3)∑_(u)^(+))and OH(X^(2)Π).Furthermore,both PD and ND demonstrate obvious energy relaxation processes of electron-to-vibration and vibration-to-vibration,and no vibration-to-rotation energy relaxation process is observed.

Time-resolved K-shell x-ray spectra of nanosecond laser-produced titanium tracer in gold plasmas

A study of a nanosecond laser irradiation on the titanium-layer-buried gold planar target is presented. The timeresolved x-ray emission spectra of titanium tracer are measured by a streaked crystal spectrometer. By comparing the simulated spectra obtained by using the FLYCHK code with the measured titanium spectra, the temporal plasma states, i.e.,the electron temperatures and densities, are deduced. To evaluate the feasibility of using the method for the characterization of Au plasma states, the deduced plasma states from the measured titanium spectra are compared with the Multi-1D hydrodynamic simulations of laser-produced Au plasmas. By comparing the measured and simulated results, an overall agreement for the electron temperatures is found, whereas there are deviations in the electron densities. The experiment–theory discrepancy may suggest that the plasma state could not be well reproduced by the Multi-1D hydrodynamic simulation, in which the radial gradient is not taken into account. Further investigations on the spectral characterization and hydrodynamic simulations of the plasma states are needed. All the measured and FLYCHK simulated spectra are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.57760/sciencedb.j00113.00032.

Detection of Rice Yellow Mottle at the Asymptomatic Stage by Hyperspectral Fluorescence and Reflectance Spectroscopies

Rice yellow mottle is considered the most destructive disease threatening rice production in Africa. Early detection of this infection in rice is essential to limit its expansion and proliferation. However, there is no research devoted to the spectral detection of rice yellow mottle virus (RYMV) infection, especially in the asymptomatic or early stages. This work proposes the use of hyperspectral fluorescence and reflectance data at leaf level for the detection of this disease in asymptomatic stages. A greenhouse experiment was therefore conducted to collect hyperspectral fluorescence and reflectance data at different stages of infection. These data allowed to calculate nine vegetation indices: one from fluorescence spectra and eight from reflectance spectra. A t-test made it possible to identify, from the second day after infection, four relevant reflectance vegetation indices to discriminate healthy leaves from those infected: these are Photochemical Reflectance Index (PRI), Transformed Chlorophyll Absorption in Reflectance Index (TCARI), Structure Intensive Pigment Index (SIPI) and Simple Ratio Pigment Index (SRPI). The fluorescence index was less sensitive in detecting infection. The four significant vegetation indices for the detection of RYMV were then used to build and evaluate models for discriminating plants according to their health status by the supervised classification of support vector machine (SVM) at different stages of infection. The maximum overall accuracy is 92.5% six days after inoculation (6 DAI). The sixth day after inoculation would be the adequate day to detect RYMV. This plants discrimination was validated by the mean reflectance spectra and by the histograms showing the differences between the average reflectance vegetation indices values of the two types of plants. Our results demonstrate the feasibility of differentiating RYMV-infected samples. They suggest that support vector machine learning models could be developed to diagnose RYMV-infected plants based on vegetation indices derived from spectral profiles at early stages of disease development.

Assembling Tunable Time-Resolved Fluorescence Layer onto Nano-Gold

The assembling of a coating of time-resolved fluorescent chelator BSPDA （ abbreviated for 4, 7-bis （ sulfhydrylphenyl）-1, 10-phenanthroline-2, 9-dicarboxylic acid） onto a nano-gold layer was demonstrated. First, BSPDA was synthesized by simple procedures, and then an approach was developed to immobilize BSPDA onto the nano-gold layer deposited on a silane modified glass substrate, whereby europium ion （Ⅲ, Eu^3＋ ） was captured and released owing to the interactive process of complexation and dissociation between BSPDA functionalized coating and Eu^3＋ solution. The fluorescence spectra and related lifetimes were determined. Also, the BSPDA functionalized coating＇s specific complexation with Eu^3＋ on the BSPDA assembly layer and the nonspecific adsorption of Eu^3＋ on the nano-gold layer were compared. These results allowed a selective complexation of Eu^3＋ by assembling a BSPDA chelating layer on the nano-gold layer; thus, a tunable time-resolved fluorescent layer was covalently attached, The results of the nanoparticle assembling and probing （or labeling） processes to specific bio-systems were very interesting and had significant implications to time-resolved-fluorescence-based detection on biosensor surfaces such as DNA chip and to arrayed light display devices.

Molecular fluorescence significantly enhanced by gold nanoparticles@zeolitic imidazolate framework-8

Noble metal nanoparticles exhibit unique surface plasmon resonance dependent optical properties.On this basis,gold nanoparticles(AuNPs)encapsulated in metal–organic frameworks(MOFs)can form AuNPs@MOFs composites to modulate the optical properties of fluorescent molecules,which is less reported.In this paper,based on the fluorescence enhancement effect of AuNPs on 2-(2-hydroxyphenyl)-1H-benzimidazole(HPBI)molecules,zeolitic imidazolate framework-8(ZIF-8)crystals with structural stability were introduced.AuNPs@ZIF-8 exhibited a significantly pronounced fluorescence enhancement of the HPBI molecules.In addition,by comparing the fluorescence characteristics of the HPBI molecules adsorbed on AuNPs@ZIF-8 and those captured in AuNPs@ZIF-8,we found that the ZIF-8 can act as a spacer layer with highly effective near-field enhancement.All our preliminary results shed light on future research on the composite structures of noble metal particles and MOFs for fluorescent probes and sensing applications.

Research of Three-Dimensional Fluorescence Spectra of RE^(3+)(RE=Eu,Tb) and Na_2WO_4 Co-doped Silica Luminescence Materials

In the preparation of this precursor tetraethlortho silicate (TEOS), sodium tungstate, ethyl alcohol, HCl and RECl3(RE=Eu,Tb) were mixed and then heated at 800 ℃ for 2 h, leading to a luminescent compound. The structure of the materials was characterized by TG-DTA and IR analysis, and the results indicate that the materials were in SiO2 network structure. Three-dimensional fluorescence spectra was used to characterize the luminescent properties of the materials. The luminescence property of doped and un-doped Eu3+or Tb3+ and Na2WO4 in silica materials were prepared and measured. The results show that good energy transfer from WO2-4 to Eu3+ ion, sensitized the luminescence intensity of Eu3+ remarkably. Tb3+ ion incorporated silica materials expressed the inverse energy transition from Tb3+ to WO2-4, however, we got the materials with homogeneous green blue fluorescent light. Finally, the energy transfer of WO2-4 and Eu3+, WO2-4 and Tb3+ were explained by energy levels diagram.

Elemental composition x-ray fluorescence analysis with a TES-based high-resolution x-ray spectrometer

The accurate analysis of the elemental composition plays a crucial role in the research of functional materials.The emitting characteristic x-ray fluorescence(XRF)photons can be used for precisely discriminating the specified element.The detection accuracy of conventional XRF methodology using semiconductor detector is limited by the energy resolution,thus posing a challenge in accurately scaling the actual energy of each XRF photon.We adopt a novel high-resolution x-ray spectrometer based on the superconducting transition-edge sensor(TES)for the XRF spectroscopy measurement of different elements.Properties including high energy resolution,high detection efficiency and precise linearity of the new spectrometer will bring significant benefits in analyzing elemental composition via XRF.In this paper,we study the Ledge emission line profiles of three adjacent rare earth elements with the evenly mixed sample of their oxide components:terbium,dysprosium and holmium.Two orders of magnitude better energy resolution are obtained compared to a commercial silicon drift detector.With this TES-based spectrometer,the spectral lines overlapped or interfered by background can be clearly distinguished,thus making the chemical component analysis more accurate and quantitative.A database of coefficient values for the line strength of the spectrum can then be constructed thereafter.Equipped with the novel XRF spectrometer and an established coefficient database,a direct analysis of the composition proportion of a certain element in an unknown sample can be achieved with high accuracy.

Evaluation of Dissolved Organic Carbon Using Synchronized Fluorescence Emission Spectra and Unsupervised Method of Principal Component Analysis (PCA) and Independent Component Analysis (ICA)

Dissolved organic matter (DOM) can be originated from autochthonous or allochthonous sources, where allochthonous DOM can be from pedogenic sources (humic substances—HSs) or anthropogenicsources (wastewater). The analysis of fluorescence emission, excitation, synchronous or excitation-emission matrix (EEM) have been used to identify the main source or probable contribution of dissolved compounds, such as humic acids (HA), fulvic acids (FA) and dissolved organic carbon (DOC) from sewage, but does not quantify. Fluorescence emission is a powerful technique to detect and qualify organic dissolved compounds but fails in quantitative aspects. In this work, we propose an in situ method for direct determination of DOC using synchronous fluorescence spectra with independent component analysis (ICA). Well known standard solutions were used for method development and validation. In this work, we show that it is possible to predict the number of independent contributions using an unsupervised method based on iterative Principal Component Analysis and Independent Component Analysis (PCA-ICA) approach over combined matrix results. Within these results it’s also possible to see that with a very small amount of independent components it is possible to describe environmental samples of HA, FA and primary productivity (PP).

Synthesis and Fluorescence Spectra of Triazolylcoumarin Fluorescent Dyes

Much attention is devoted to fluorescent dyes especially those with potential in versatile applications.Reactions under "click" conditions between nonfluorescent 3-azidocoumarins and terminal alkynes produced 3-(1,2,3-triazol-1-yl)coumarins,a novel type of fluorescent dyes with intense fluorescence.The structures of the new coumarins were characterized by 1H NMR,MS,and IR spectra.Fluorescence spectra measurement demonstrated excellent fluorescence performance of the triazolylcoumarins and this click reaction is a promising candidate for bioconjugation and bioimaging applications since both azide and alkynes are quite inert to biological systems.

TEMPERATURE DEPENDENCE OF THE FLUORESCENCE SPECTRA OF LADDERLIKE POLYPHENYLSILSESQUIOXANE AND LADDERLIKE 1,4-PHENYLENE-BRIDGED POLYVINYLSILOXANE

Fluorescence spectra of ladderlike polyphenylsilsesquioxane (LPPS) and ladderlike 1,4-phenylene-bridged polyvinylsiloxane (LPPVS) have been measured as a function of temperature (4-55 degreesC), in dilute tetrahydrofuran solution. The excimer (IF) to monomer (I-M) intensity ratio (I-E/I-M) of LPPS dilute solution shows a double linear Arrhenius plot with a break point ascribable to a transition temperature Tt. This behavior has not been found for single chain polyorganosiloxanes. When In/(E) of LPPS was plotted against 1/T, it also gave a double linear plot with one break point, which was found in single chain polyorganosiloxanes. The different behaviors between LPPS and single chain polyorganosiloxanes may be mainly attributed to the relatively rigid double-chain macromolecular backbone of LPPS. However, the 1n(I-E/I-M) of dilute LPPVS solution versus 1/T shows a simple linear variation with a positive slope which confirms our proposition. The difference between the fluorescence results of LPPS and those of LPPVS may possibly derive from their structure differences and cooperative motion in backbone chain bonds.

Interaction of 4-aminosalicylic Acid and Surfactants in Aqueous Solutions Using UV-Vis Spectra and Steady-state Fluorescence Spectroscopy

The interactions of 4-aminosalicylic acid （4-ASA） and surfactants in aqueous solutions were investigated by using UV-Vis spectra and steady-state fluorescence spectroscopy.The results showed that the strongest peak at UV-vis spectra of 4-ASA aqueous solution in the presence of cationic surfactant and cetyltrimethyl ammonium bromide （CTAB） appeared at 206 nm and took a red shift from 206 nm to 221 nm with the increase of 4-ASA concentrations from 0.8×10-5 to 4.4×10-4 mol/L.Similarly,the strongest peak at UV-vis spectra of 4-ASA aqueous solution in the presence of nonionic surfactant and polyvinylpyrrolidone （PVP） appeared at 206 nm and took a red shift from 206 nm to 219 nm with the increase of 4-ASA concentrations from 0.8×10-5 to 4.4×10-4 mol/L.However,the similar phenomena did not appeared in the presence of anion surfactant,sodium dodecyl sulfate （SDS）,the UV-vis spectra of 4-ASA aqueous solution remained the same peak position and the peak value increased with the 4-ASA concentration increase.The results could be attributed to the electrostatic attraction between 4-ASA and CTAB or PVP,as well as the electrostatic repulsion between 4-ASA and SDS.Furthermore,the value of critical micelle concentration （CMC） of surfactants in the presence of 4-ASA was determined with Fluorescence method.The first and second CMC of CTAB was 1.2×10-4 M and 2.4×10-4 M,respectively.The first and second CMC of PVP was 1.2×10-4 M and 2.8×10-4 M.SDS realized the multiple micellizations to form multiple CMC.

Fluorescence Spectra of the Poly (N-vinylcarbazole)Obtained with Asymmetric Polymerization

The fluorescence spectra of the poly (N-vinylcarbazole) in solution obtained with chirally organic salts or acid as catalyst or initiator [ (-)Sp: (-)-Sparteine, (+)CSA: D- (+)Camphor-10-sulfonic acid)], respectively, have been investigated. It is found that the two emission peaks at the longer wavelength (lambda max, ca, 415nm) and the shorter wavelength (lambda max, ca, 370nm) are assigned to the sandwich excimer and second excimer (partial overlap) fluorescence, respectively. The sandwich excimer and partially overlapped excimer are attributed to a fully overlapped structure of neighbouring carbazole chromophores in a totally elipsed conformation of the isotactic sequence, and partially overlapped structure of the syndiotactic sequence. The estimated values of I-415/I-370 and isotactic sequence content by using the fluorescence spectra are in the order: (-)Sp(+) (+)CSA(-)> (+)CSA(-)> (-)Sp(+)ClO(4)(-) (no peak at 415nm for AIBN).

Characteristics of the ThreeDimensional Fluorescence Spectra of Fossil Fuels

We have found some fluorescence characteristics of fossil fuels based on the contour maps of the three dimensional fluorescence spectra of their non quenching samples. The common fluorescence characteristic is that the main peaks of various fossil fuels are located in the vicinity of excitation/emission wavelength pair 228nm/340nm.The diversity of fluorescence characteristics can be represented with several indexes α,K,F and R ,and these indexes provide measurable parameters for division of fluorescence fingerprints of fossil fuels. The fluorescence fingerprints of fossil fuels can be divided into five models named O,B,Q,P and G that are corresponding to condensate oil, light oil, heavy oil, coal and natural gas, respectively. The technique has a potential application in study of environment pollution on crude oil and geochemical exploration of fossil fuels.

Time-Resolved Photoluminescence Spectra of Porous Si

he photoluminescence spectra of porous Si have been studied. Its timere-solved luminescence spectra show a red shift of luminescencc peak with increasingdelay time after exciting and a nonexponential decay. Several spectral bands withdifferent Gaussian center appear by means of the decomposition of a spetrum. Theresuits of our experiments show quantum confined characters in porous Si, and wespeculate that the short wavelength band at 465 nm is the direct band froni P_(15) toP_(25)

X-RAY FLUORESCENCE SPECTRA ANALYSIS ON THE STRUCTURE AROUND Ti^(4+) OF BaO-SiO_2-B_2O_3-TiO_2 SYSTEM GLASSES

The structure around Ti^(4+) in Bao-SiO_2 -B_2O_3-TiO_2 had been studied by X-ray fluorescence spectra. The results show that the Ti^(4+) mainly exists in the [TiO_4] and enters the network of [SiO_4]. [TiO_4] has the tendency to change to [TiO_6] with the increase of TiO_2 con-tent. When the TiO_2 content increases to about 20mol% the tendency reaches its maximum.

STUDIES ON FLUORESCENCE SPECTRA OF SAMARIUM EUROPIUM TERBIUM AND DYSPROSIUM WITH BENZOYL UREA DERIVATIVES AND PHENANTHROLINE

Rare earth chelates of benzoyl urea derivatives were prepared in ethanol and fluorescence spectra of these chelates were studied in detail. A composition of [RE(BU)_3Phen] (NO_3)_3 was obtained. Correlation between chemical properties of ligands, chelates and spectroscopy was discussed. Intramolecular energy transfer in rare earth chelates was explained.

A portable optical sensing system for rapid detection of fluorescence spectra

Development of a prototype of a portable optical sensing system is presented for fast detecting of samples’fluorescence spectra.A compact configuration is achieved by integrating a small spectrometer,a microcontroller,a Universal Serial Bus(USB)Host Shield,a network module,and a web server.The fluorescence spectra of a tested sample can be obtained.Then the test data are sent through network communication to our Cloud Server which can store the data for further analyses.With this configuration,test results can be revealed in a short time and downloaded by users to their laptops,tablets or cellphones anytime and anywhere.

The Fluorescence spectra of Iron-arene complex photo initiator

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An ultrasensitive time-resolved fluorescent immunoassay method for determination aflatoxins B1 in edible oil

Edible oil is one major nutritional ingredient to human and widely consumed directly. The contamination of aflatoxin B1 （AFB1） in edible oils has been attracted exten-sive efforts due to its hazard to human health and life. To avoid the digestion of edible oils contaminated by AFB1 the development of rapid and sensitive sensing method for AFB1 is required. Herein, a quantitative, sensitive and rapid method for AFB1 detection in edible oils was proposed by using ultrasensitive time-resolved fluorescent immunosensing （TRFIS） method. This method poses unique advantages from both time-resolved fluorescent sens-ing method and immunochromatographic assay format. The nanospheres were modified with fluorescent europium and then captured the home-made monoclonal antibody against AFB1 （3G1）. After optimization, by using a competitive immunosensing manner, this TRFIS method has a detectable linear range of 0.54-20.0 μg/kg with minimum detectable concen-tration of 0.18μg/kg. It can be completed merely within 10 min with recovery from 87.0% to 121.9%. The agreement was observed between the results by TRFIS and high perfor-mance liquid chromatography （HPLC） methods. This research provides a promising sens-ing method for sensitive and rapid determining AFB1 in edible oils.