Excitation Wavelength Λex Research Articles

The formation of complexes with albumin increases the stability of the protoporphyrin IX spectra.

Photodynamic therapy is a high-target, low-invasive treatment utilized to manage a variety of malignant diseases and precancerous lesions. Protoporphyrin IX (PpIX) is one of the most important photosensitizers used in photodynamic therapy, carried to the cancer tissue by serum albumin. Its delivery by transport protein is one of the major factors in determining the efficacy of photodynamic therapy. The distribution of the albumin-PpIX complexes to the target tissue enables the accomplishment of an optimal PDT effect. This study aimed to assess in vitro the stability of spectrofluorimetric spectra of albumin-PpIX complexes. The experiment used three chemicals: PpIX, human serum albumin (HSA), and bovine serum albumin (BSA). Spectral data was recorded using a Kontron SFM-25 Instrument AG, at two excitation wavelengths λex=280 nm and 295 nm. A concentration of 1x10-5M of PpIX, in combination with 1.25x10-6M of HSA and 4x10-7M of BSA, have been recorded repetitively for ten days and compared to the initial spectrum. The maximum of PpIX fluorescence changed significantly on the first day following sample preparation. The maximum of PpIX - serum albumin complex was stable 10 and 4 days for HSA and 5 and 2 days for BSA for λex=280 nm and 295 nm, respectively. The formation of a complex between PpIX and serum albumin was seen to extend the stability of the spectrofluorimetric spectrum. However, a less significant effect was observed in the case of BSA, which could most plausibly be attributed to the variations in primary structure between HSA and BSA, leading to discernible variations in spectroscopic measurements.

Strong resonance interaction in 4-{4-[2-(3-dicyanomethylene-5,5-dimethyl-cyclohex-1-enyl)-vinyl]-phenoxy}-butyric acid. Structural, electrochemistry and spectroscopic properties complemented by Natural Bond Orbital and Hirshfeld surface analysis

The present investigation deals with the synthesis and characterization of (E)-4-(4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenoxy)butanoic acid (SLN-01) and its electrochemical and structural study. The compound SLN-01, has been characterized by UV, FTIR, and multinuclear (1H and 13C) NMR spectroscopic studies. DFT calculations were used to estimate redox potential and band gap energies of SLN-01. It's molecular and crystal structures were determined by single-crystal X-ray analysis. The compound (E)-4-(4-(2-(3-(Dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenoxy) butanoic acid (SLN-01) was crystallized in the triclinic geometry. The Hirshfeld surface analysis was conducted to confirm the supramolecular association formed by the individual conformers and overall packing in the crystal. Natural Bond Orbital population analysis was performed to understand the electronic interactions between the donor and acceptor moieties in the molecule. The targeted compound exhibited a strong absorption at 416 nm (ε= 67762 ± 4600 L mol−1 cm−1) with emission (λem) at 575 nm (at excitation wavelength λex= 430 nm).

Investigation of structural, optical, morphological, photoluminescence and antimicrobial properties of SrAl2O4:Eu2+ nanophosphor by using urea fuel combustion method

In the present study, the Sr1−xAl2O4:Eux (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) phosphor were synthesized by urea fuel combustion method at 580 °C temperature with very high brightness and long after glow. The structural studies carried out using XRD technique shows that the sample is single phased in nature and it gets crystallized into monoclinic phase with standard JCPDS 34-0379 card. The oxide formation was examined using FTIR technique. UV–Visible spectroscopy has been used to study the optical band gap of material, it’s value in the current case, Sr1−xAl2O4:Eux (x = 0.05) is 3.78 eV. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirm the formation of nano particle, with average particle size around 6–25 nm. The elemental composition was confirmed by using Energy Dispersive X-ray (EDX) technique. The photo-luminescence study revealed that it gives broad emission spectra using excitation wavelength λex = 365 nm. It is observed that the Sr1−xAl2O4:Eux (x = 0.05) phosphor give maximum emission intensity and it can be regulated as green (0.23, 0.49) emission with the colour temperature 3224 K, CRI 78, and colour purity 60.69%. The spectra are intense and lie in the visible range. The green lights can regulate the circadian rhythm through melatonin, and it is also suitable for green LED and other optoelectronic devices. The Sr1−xAl2O4:Eux (x = 0.00 and 0.05) phosphor behaves like eco-materials, because nano particles of Sr1−xAl2O4:Eux (x = 0.05) does not show antimicrobial activity.

Preparation and performance study of rhodamine B naphthylamide, a fluorescent probe, for the detection of Fe3.

Fe3+ is essential for humans, and its deficiency or excess can be harmful to human health; thus, it is crucial to detect Fe3+. Herein, a novel 1,8-naphthylimide rhodamine-based fluorescent probe (NA-RhBEA) was prepared from rhodamine B, anhydrous ethylenediamine, and 1,8-naphthoic anhydride. This fluorescent probe complexes Fe3+ with N and O on the carboxyl groups of its spironolactam structure and part of the 1,8-naphthalenedicarboxylic anhydride structure, which results in spironolactam ring-opening and fluorescence. NA-RhBEA has high selectivity for Fe3+ in ethanol/buffer solution (4 : 1, v/v), and fluorescence is detected at an excitation wavelength λEX = 500 nm, an absorption peak appears at 585 nm, and a significant color change appears. The effect of the fluorescence intensity of Fe3+ under a series of different concentration conditions was investigated, and it was concluded that the fluorescence intensity increased with increasing Fe3+ concentration in the range of 0-500 μmol, and its detection limit was 0.84 μmol L-1. In addition, we explored the detection ability of NA-RhBEA in solutions with different pH values, mixed metal ions, and different solvents, and the results showed that the fluorescent sensor also has good anti-interference properties and some practical applicability.

Quenching of Protein Fluorescence by Fullerenol C60(OH)36 Nanoparticles.

The effect of the interaction between fullerenol C60(OH)36 (FUL) and alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae and human serum albumin (HSA) was studied by absorption spectroscopy, fluorescence spectroscopy, and time-resolved fluorescence spectroscopy. As shown in the study, the fluorescence intensities of ADH and HSA at excitation wavelengths λex = 280 nm (Trp, Tyr) and λex = 295 nm (Trp) are decreased with the increase in the FUL concentration. The results of time-resolved measurements indicate that both quenching mechanisms, dynamic and static, are present. The binding constant Kb and the number of binding sites were obtained for HSA and ADH. Thus, the results indicated the formation of FUL complexes and proteins. However, the binding of FUL to HSA is much stronger than that of ADH. The transfer of energy from the protein to FUL was also proved.

Highly-sensitive lifetime optical thermometers based on Nd3+, Yb3+:YF3 phosphors

Optical thermometers based on Nd3+ (0.5 mol.%), Yb3+ (1.0, 2,0, 4.0, and 8.0 mol.%):YF3 nano-phosphors were studied in the 80–320 K temperature range. The Nd3+, Yb3+:YF3 phosphors were nanoparticles having 48 ± 1 nm average diameter with the orthorhombic crystal structure. The effective luminescence lifetime (τeff) of 4F3/2 of Nd3+ (4F3/2 – 4I9/2 transition, λem = 866 nm) was taken as a temperature-dependent parameter. The excitation wavelength λex = 355 nm corresponds to 4I9/2 – 4D3/2 absorption band of Nd3+ (non-resonant excitation). It was revealed that the τeff decreases with the temperature decrease in the 80–260 K range. In turn, τeff temperature dependence in the 260–320 K range is less pronounced. The temperature-dependent X-ray diffraction (XRD) experiments revealed that the XRD patterns shift toward fewer angles as temperature increases. This phenomenon was explained by the temperature expansion of the crystal lattice. At lower temperatures the distance between Nd3+ and Yb3+ is less in comparison to the distance at higher temperatures. At shorter distances the quenching of τeff Nd3+ is more efficient hence the τeff is less. It was suggested that the contribution of phonon-assisted energy transfer between Nd3+ and Yb3+ has less impact on the τeff temperature dependence. Finally, the Nd3+, Yb3+:YF3 phosphors demonstrated the highest performances in the 100–250 K range. Particularly, Nd3+ (0.5%), Yb3+ (8.0%):YF3 and Nd3+ (0.5%), Yb3+ (1.0%):YF3 samples showed the highest Sr values (0.80 μ%/K (at 80 K) and 0.58%/K (at 148 K), respectively.

Structural, luminescent properties and Judd-Ofelt analysis of CaMgSiO4:Eu3+ phosphor for solid state lighting

A series of Eu3+ doped calcium magnesium silicate (CaMgSiO4) phosphor samples were successfully prepared via solid state synthesis technique. Their structural and morphological studies were investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) measurements. Phase structure and phase purity of sample were investigated by Rietveld refinement method. The vibrational and bonding behavior of silicate groups were confirmed by Fourier transform infrared (FTIR) and Raman spectroscopy. The luminescent properties of prepared samples were studied by photoluminescence (PL) and thermoluminescence (TL) characteristics. The emission spectra recorded under the excitation wavelength λex = 396 nm. The highest emission peak was observed at 595 nm which corresponds to the 5D0 → 7F1 transition of Eu3+ ions with selection rule ΔJ = 1. The concentration quenching and energy transfer mechanisms were elucidated by Blasse and Dexter's formula. The photometric parameters correlated color temperature (CCT), color rendering index (CRI) and color purity (CP) were computed using CIE chromaticity co-ordinate diagram. In addition, Judd-Ofelt (JO) parameters (Ω2, Ω4) and other derived radiative parameters were calculated using Judd-Ofelt theory from the PL emission spectra. Time resolved fluorescence spectra were carried out to determine the decay lifetime of the samples. The prepared samples are expected to be suitable candidates for the applications as solid state devices, lighting and optical displays.

Photodynamic Inactivation of E. coli Bacteria via Carbon Nanodots.

The increasing development of antibiotic resistance in bacteria has been a major problem for years, both in human and veterinary medicine. Prophylactic measures, such as the use of vaccines, are of great importance in reducing the use of antibiotics in livestock. These vaccines are mainly produced based on formaldehyde inactivation. However, the latter damages the recognition elements of the bacterial proteins and thus could reduce the immune response in the animal. An alternative inactivation method developed in this work is based on gentle photodynamic inactivation using carbon nanodots (CNDs) at excitation wavelengths λex > 290 nm. The photodynamic inactivation was characterized on the nonvirulent laboratory strain Escherichia coli K12 using synthesized CNDs. For a gentle inactivation, the CNDs must be absorbed into the cytoplasm of the E. coli cell. Thus, the inactivation through photoinduced formation of reactive oxygen species only takes place inside the bacterium, which means that the outer membrane is neither damaged nor altered. The loading of the CNDs into E. coli was examined using fluorescence microscopy. Complete loading of the bacterial cells could be achieved in less than 10 min. These studies revealed a reversible uptake process allowing the recovery and reuse of the CNDs after irradiation and before the administration of the vaccine. The success of photodynamic inactivation was verified by viability assays on agar. In a homemade flow photoreactor, the fastest successful irradiation of the bacteria could be carried out in 34 s. Therefore, the photodynamic inactivation based on CNDs is very effective. The membrane integrity of the bacteria after irradiation was verified by slide agglutination and atomic force microscopy. The method developed for the laboratory strain E. coli K12 could then be successfully applied to the important avian pathogens Bordetella avium and Ornithobacterium rhinotracheale to aid the development of novel vaccines.

Spectroscopic Studies of Quinobenzothiazine Derivative in Terms of the In Vitro Interaction with Selected Human Plasma Proteins. Part 1.

Plasma proteins play a fundamental role in living organisms. They participate in the transport of endogenous and exogenous substances, especially drugs. 5-alkyl-12(H)-quino[3,4-b][1,4]benzothiazinium salts, have been synthesized as potential anticancer substances used for cancer treatment. Most anticancer substances generate a toxic effect on the human body. In order to check the toxicity and therapeutic dosage of these chemicals, the study of ligand binding to plasma proteins is very relevant. The present work presents the first comparative analysis of the binding of one of the 5-alkyl-12(H)-quino[3,4-b][1,4]benzothiazinium derivatives (Salt1) with human serum albumin (HSA), α-1-acid glycoprotein (AGP) and human gamma globulin (HGG), assessed using fluorescence, UV-Vis and CD spectroscopy. In order to mimic in vivo ligand–protein binding, control normal serum (CNS) was used. Based on the obtained data, the Salt1 binding sites in the tertiary structure of all plasma proteins and control normal serum were identified. Both the association constants (Ka) and the number of binding site classes (n) were calculated using the Klotz method. The strongest complex formed was Salt1–AGPcomplex (Ka = 7.35·104 and 7.86·104 mol·L−1 at excitation wavelengths λex of 275 and 295 nm, respectively). Lower values were obtained for Salt1–HSAcomplex (Ka = 2.45·104 and 2.71·104 mol·L−1) and Salt1–HGGcomplex (Ka = 1.41·104 and 1.33·104 mol·L−1) at excitation wavelengths λex of 275 and 295 nm, respectively, which is a positive phenomenon and contributes to the prolonged action of the drug. Salt1 probably binds to the HSA molecule in Sudlow sites I and II; for the remaining plasma proteins studied, only one binding site was observed. Moreover, using circular dichroism (CD), fluorescence and UV-Vis spectroscopy, no effect on the secondary and tertiary structures of proteins in the absence or presence of Salt1 has been demonstrated. Despite the fact that the conducted studies are basic, from the scientific point of view they are novel and encourage further in vitro and in vivo investigations. As a next part of the study (Part 2), the second new synthetized quinobenzothiazine derivative (Salt2) will be analyzed and published.

Absolute luminescence quantum yield for nanosized carbon particles in water as a function of excitation wavelength.

The absolute luminescence quantum yield Q as a function of excitation wavelength λex in a wide spectral range 270-470nm was measured for the first time for the group of carbon nanoparticles dispersed in water: carbon dots (CD), detonation nanodiamonds (DND), as well as detonation nanodiamonds decorated with carbon dots (CD-DND). The luminescence quantum yield for DND increased after functionalization; the CD-decorated DND demonstrated significantly higher Q values in the UV region of excitation. We found that the quantum yield for CD luminescence is 4-8 times higher than that for CD-DND luminescence, and 20 times higher than that for DND luminescence. Roughly three spectral regions can be distinguished within the Q(λex): below 330nm, 330-390nm and 390-470nm. Conclusions are drawn about the number of chromophores of the studied nanoparticles and transfer of photoexcitation energy in the systems under consideration.

Luminescent properties of Sm3+ doped metal fluoro phosphate glasses

Trivalent Samarium doped multi-component Cadmium Lead Sodium Fluoro-Phosphate glass was prepared and characterized through optical absorption, emission and excitation measurements. With the support of Judd-Ofelt theory, the intensity parameters and other radiative parameters were determined using optical absorption spectra from visible region to NIR region and reasonable less deviation obtained between the experimental and calculated oscillator strengths. The emission and excitation spectra of Sm3+ have been recorded under the excitation wavelength λex =399 nm and the emission wavelength λem =596 nm. The emission of Sm3+ in this phosphate host is assigned to the transition from 4G5/2 to 6H5/2, 6H7/2, 6H9/2 and 6H11/2 levels and relative parameters like branching ratio, emission cross section were calculated. In addition to that 1 mol% of MgO also added to the host and compared with the obtained results. GSm5 glass emits high intense red emission for 4G5/2 → 6H7/2 transition suggests the suitability of these glasses for red light emission or laser applications in visible region.

Time-resolved photoluminescence of pH-sensitive carbon dots

Time-resolved photoluminescence emission were performed to study the ≥100 ps time-scale photophysics of water soluble carbon dots (CDs) dispersed in different pH solutions. Excitation of the core and high-energy edge states at excitation wavelengths λex ≤ 350 nm produce hole-electron excitonic charge-carriers but do not yield any photoluminescence emission, implying efficient non-radiative recombination mechanisms for the charge-carriers. Using λex ∼375 nm, surface fluorophores as well as low-lying edge-states are excited, producing emission over a broad range. However, the emission characteristics vary strongly depending on the pH condition and the choice of excitation wavelength. In particular, the edge state emission is abruptly extinguished at pH ≥ 5, which also marks the onset of deprotonation of surface-bound -COOH groups of the CDs, indicating that the -COO- anionic centers promote quenching of edge-state emission. Using λex ∼450 nm, only the surface fluorophores are excited. The deprotonation of phenolic -OH group at pH > 9 causes a sharp red-shift in the emission spectra at all excitation wavelengths. The pH-sensitive emission behavior of the CDs enable them to serve as optical pH sensors.

Photoluminescence properties of (Y1−xCex)3Al5O12 (x = 0.005–0.03) nanophosphors and transparent ceramic by a homogeneous co-precipitation method

Fine and dispersed (Y1−xCex)3Al5O12 (x = 0.005–0.03) nanophosphors were co-precipitated uniformly using a homogeneous co-precipitation process. With an excitation wavelength λex of 455 nm, the YAG:Ce phosphors showed strong luminescence with maxima at 550 nm in the range of 475–650 nm. The emission intensity becomes stronger due to the improved crystallinity and decreased surface defects of the resultant phosphors with increasing calcination temperatures. The quenching concentration of Ce3+ was 1.5 at% and the quenching mechanism was Ce–Ce interactions and lattice defects. The fluorescence lifetime of the phosphors decreased with increasing Ce concentrations and temperatures. The mechanism is influenced by defects both in surface and body. The resultant YAG:Ce powders showed an excellent sintering activity and can be sintered into transparent ceramic under vacuum technique. Compared with the phosphors, the transparent ceramic exhibits stronger luminescence properties and shorter fluorescence lifetime.

Optically Controlled Electron-Transfer Reaction Kinetics and Solvation Dynamics: Effect of Franck-Condon States.

Experimental results for optically controlled electron-transfer reaction kinetics (ETRK) and nonequilibrium solvation dynamics (NESD) of Coumarin 480 in DMPC vesicle show their dependence on excitation wavelength λex. However, the celebrated Marcus theory and linear-response-theory-based approaches for ETRK and NESD, respectively, predict both of the processes to be independent of λex. The above said lacuna in these theories prompted us to develop a novel theory in 1D space, where the effect of innumerable Franck-Condon states is included through λex. The present theory not only sheds light on the origin of failure of the existing theories but also gives the correct trend for the effect of λex on ETRK and NESD. More importantly, the calculated results of NESD are in excellent agreement with the experimental results for different values of λex. The new theory will therefore advance the knowledge of scientific community on the dynamics of photoinduced nonequilibrium processes.

Time-Resolved Laser-Induced Fluorescence Spectroscopy as a Guidance Tool for Laser Lithotripsy of Gallbladder Stones.

Although laser lithotripsy for fragmentation of gallbladder stones has been applied successfully in many clinical situations, this approach has two major limitations: (1) the potential to damage or perforate the bile duct and (2) the efficiency can be affected by the chemical composition of the gallstones. The present study evaluated the use of time-resolved laser-induced fluorescence spectroscopy to classify stone types and distinguish stone from tissue. Ex vivo time-resolved laser-induced fluorescence analysis (excitation wavelength λex = 400 nm and emission wavelength = 450-700 nm) of 54 gallbladder stones and seven gallbladder tissue samples was conducted. The spectral and temporal parameters were analyzed using linear discrimination analysis (LDA) to differentiate stone from tissue and to classify different stone types using two wavelength regions (λ1 = 510-530 nm and λ2 = 550-570 nm). Examination of 54 gallbladder stones and seven gallbladder tissue samples showed a significant difference in spectral- and temporal-derived parameters. The data were classified using LDA, and the overall accuracy was 94.88%, 84.39%, and 85.79% for both spectral and temporal parameters, only spectral parameters, and only temporal parameters, respectively. Our findings establish the feasibility of using time-resolved laser-induced fluorescence spectroscopy as a tool to identify gallbladder stone types and as a stone-tissue detection system to improve the effectiveness of laser lithotripsy procedures and reduce the risk of damaging biliary tract tissues.

Identification and origin of visible transitions in one dimensional (1D) ZnO nanostructures: Excitation wavelength and morphology dependence study

In this present work, one dimensional (1D) ZnO nanostructures were synthesized by mechanical assisted thermal decomposition process. The samples were characterized by transmission electron microscopy (TEM) for morphology, high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) for structural characterization. Photoluminescence (PL) and Photoluminescence spectra evolution was studied as a function of (i) excitation wavelength (λEx: 310–370nm) and (ii) morphology (nanoneedles and nanorods). PL spectra were observed to be highly asymmetric with strong dependence on excitation wavelength (λEx). PL spectra categorized into two types as a function of excitation wavelength (λEx): I. λEx≤345nm and II. λEx≥350nm.The PL spectra were deconvoluted into multiple Gaussian components for each excitation wavelength. The position of each component is a signature of its origin and corresponds to specific visible transition. The transition involving origin from conduction band (CB) are absent for excitation wavelength λEx≥350nm. The tunable photoresponse is achieved in 1D ZnO nanostructures by varying (i) excitation wavelength and (ii) morphology: nanoneedles to nanorods. PL intensity increases as aspect ratio decrease from nanoneedles to nanorods morphology. This is attributed to non-radiative quenching by near surface defects.

Eu2+ -induced enhancement of defect luminescence of ZnS.

The Eu2+ -induced enhancement of defect luminescence of ZnS was studied in this work. While photoluminescence (PL) spectra exhibited 460nm and 520nm emissions in both ZnS and ZnS:Eu nanophosphors, different excitation characteristics were shown in their photoluminescence excitation (PLE) spectra. In ZnS nanophosphors, there was no excitation signal in the PLE spectra at the excitation wavelength λex >337nm (the bandgap energy 3.68eV of ZnS); while in ZnS:Eu nanophosphors, two excitation bands appeared that were centered at 365nm and 410nm. Compared with ZnS nanophosphors, the 520nm emission in the PL spectra was relatively enhanced in ZnS:Eu nanophosphors and, furthermore, in ZnS:Eu nanophosphors the 460nm and 520nm emissions increased more than 10 times in intensity. The reasons for these differences were analyzed. It is believed that the absorption of Eu2+ intra-ion transition and subsequent energy transfer to sulfur vacancy, led to the relative enhancement of the 520nm emission in ZnS:Eu nanophosphors. In addition, more importantly, Eu2+ acceptor-bound excitons are formed in ZnS:Eu nanophosphors and their excited levels serve as the intermediate state of electronic relaxation, which decreases non-radiative electronic relaxation and thus increases the intensity of the 460nm and 520nm emission dramatically. In summary, the results in this work indicate a new mechanism for the enhancement of defect luminescence of ZnS in Eu2+ -doped ZnS nanophosphors. Copyright © 2016 John Wiley & Sons, Ltd.

Synthesis and luminescence properties of Ca5(PO4)3Cl:Eu2+ phosphor for solid state lighting

A novel method to prepare Eu2+ doped chlorapatite phosphor Ca5(PO4)3Cl useful for solid state lighting has been given in this paper. The phosphor was synthesized by the Pechini (citrate gel) method which turned out to be more efficient than the conventional high temperature solid state reaction. The results of the photoluminescence (PL) investigation revealed that it was possible to efficiently excite the phosphor by a UV–visible light from 220 to 430nm; the phosphor exhibited a bright blue emission at the wavelength λem=456nm for the excitation wavelength λex=350nm of near-ultraviolet light. The developed phosphor emits in blue and, hence, could provide one of the three (RGB) primary color components in a phosphor-converted LED-producing white light.

High-Performance Simultaneous Two-Photon Absorption Upconverted Stimulated Single-Component Sr2V2O7 Phosphor for White LEDs

Notwithstanding the wide use of white light-emitting diodes (w-LEDs), conventionally consisting of multiple emitting components, some inevitable issues still exist nowadays, such as the intrinsic color balance, device complexity, and high cost associated with such multiple emitting components. We have synthesized simultaneous two-photon absorption upconverted stimulated single-component Sr2V2O7 phosphor for use in w-LEDs. Due to the photon avalanche upconversion, the as-grown phosphor exhibits an enhanced photoluminescence spectrum in the range of 400 nm to 650 nm for white light when excited by red light at 693 nm. Moreover, when evenly dispersed in polyethylene glycol dispersant, the as-grown phosphor simultaneously produced strong visible white light when using an excitation wavelength λex of 693 nm, suggesting a possible route to produce w-LEDs by using red chips as an excellent substitute for traditional w-LEDs with multiple emitting components based on rare-earth metals. Finally, density functional calculations were performed using the generalized gradient approximation to study the electronic structure of Sr2V2O7 crystal. A reasonable model is proposed to explain the two-photon absorption luminescence mechanism.

Spectral measurement of acceptor-to-donor extinction coefficient ratio in living cells

This report presents a simple method named as sp-ECR to determine the molar extinction coefficient ratio (γ(λex)) of acceptor-to-donor in living cells at excitation wavelength λex, which is closely associated with the acceptor cross-excitation, the hardest issue of FRET quantification. sp-ECR determines γ(λex) by spectrally unmixing the emission spectrum of a donor–acceptor tandem construct under λex excitation without any additional references, such that this method can be performed under optimal imaging condition. We used sp-ECR to measure the γ(458) of Venus/Cerulean in living HepG2 cells on a confocal microscope, and the measured values were consistent with those obtained by lux-FRET method. We also used sp-ECR to measure the γ(458) values of Venus/Cerulean and YFP/CFP as well as YFP/GFP, the commonly used FRET FPs pairs in other two kinds of cancer cell lines on the confocal microscope, and found that the extinction coefficients of FPs depended on cell lines. After predetermining the γ(458) of Venus to ECFP, we used sp-ECR method to monitor the staurosporine (STS)-induced dynamical caspase-3 activation in single live A549 cells expressing SCAT3 by spectrally resolving the absolute FRET efficiency of SCAT3, and found that STS-induced caspase-3 activation in single cells is a very rapid process within 20min.