Dependence Of Fluorescence Intensity Research Articles

Using reflectometry to minimize the dependence of fluorescence intensity on optical absorption and scattering.

The total diffuse reflectance RT and the effective attenuation coefficient µeff of an optically diffuse medium map uniquely onto its absorption and reduced scattering coefficients. Using this premise, we developed a methodology where RT and the slope of the logarithmic spatially resolved reflectance, a quantity related to µeff, are the inputs of a look-up table to correct the dependence of fluorescent signals on the media's optical properties. This methodology does not require an estimation of the medium's optical property, avoiding elaborate simulations and their errors to offer accurate and fast corrections. The experimental demonstration of our method yielded a mean relative error in fluorophore concentrations of less than 4% over a wide range of optical property variations. We discuss how the method developed can be employed to improve image fidelity and fluorochrome quantification in fluorescence molecular imaging clinical applications.

Crystallization Behavior of Semicrystalline Polymers Characterized by an In Situ Fluorescence Technique and its Sensing Mechanism

AbstractIn this study, fluorescence spectroscopy is used to study the bulk nonisothermal and isothermal crystallization of poly(L‐lactic acid) (PLLA) by monitoring in situ, the temperature (T)‐ and time (t)‐dependent fluorescence intensity of the fluorophores incorporated into the PLLA matrix, respectively. The crystallization behavior characterized by fluorescence resembles those measured by conventional differential scanning calorimetry, confirming the validity of this fluorescence technique for sensing crystallization. Combined in situ fluorescence results and ex situ X‐ray diffraction characterizations demonstrate that this fluorescence technique shows great sensitivity not only to the degree of crystallinity but also to the crystalline microstructures formed during crystallization (e.g., α vs α' form PLLA crystals). Moreover, complementary fluorescence microscopy helps reveal the fluorescence's intrinsic crystallization sensing mechanism: As crystals form during crystallization, the bulky fluorescent probes excluded from the crystalline regions reside in the rigid/mobile amorphous (i.e., non‐crystalline) regions of the resulting semicrystalline matrix, and their intramolecular motions are restricted by the neighboring crystalline domains; and thus, their fluorescence intensity is greatly enhanced upon crystallization. Owing to its high sensitivity, fluorescence is powerful for studying the crystallization behavior of ultrathin polymer films (e.g., 75 nm) and elucidating confinement and interfacial effects through future studies.

An Integrated Temperature-Feedback Photothermal Therapy Platform Based on Dual-Functional Rare Earth-Doped NaSrGd(MoO4)3 Phosphors

Nd3+ doped and Er3+/Yb3+ codoped NaSrGd(MoO4)3 (NSGM) phosphors were synthesized and used to build an integrated temperature-feedback photothermal therapy platform. Intense green upconversion emissions were observed in Er3+/Yb3+-codoped NSGM phosphors and used to construct an all-fiber temperature sensing probe. The temperature dependent fluorescence intensity ratio (FIR) calibration curve was established and the absolute temperature sensitivity Sa reached the maximum value of 0.013 K–1 at 423 K. The photothermal conversion performance of NSGM:Nd3+ phosphors could be easily modified by altering Nd3+ doping concentration and 808 nm laser irradiation power. An integrated all-fiber photothermal temperature measurement platform was built and the temperature measurement error was smaller than ±1 K, which could simultaneously achieve photothermal conversion and temperature measurement in narrow spaces and was expected to be used in local photothermal therapy applications.

Nonmonotonic temperature dependence of fluorescence intensity of carbon dots in a glycerol solution

The effect of temperature on the fluorescence of carbon dot colloidal solution in glycerol has been studied. The dots were prepared by pyrolysis of a Nile Red laser dye using mesoporous silica as a template. It is established that the temperature dependence of the intensity of dominant emission peak is nontrivial: as the temperature of the solution rises, the initial quenching of the fluorescence is then replaced by its enhancement to the initial value. A three-level model of electronic states is considered, within which the observed temperature dependence of fluorescence is quantitatively described and the energies of nonradiative deactivation and activation of the emissive state are estimated. The nature of the electronic state responsible for the nonradiative activation of the emissive state is discussed. The possible influence of hydrogen bonds in the solute-solvent system on the temperature behavior of the CD fluorescence is also considered. A pronounced solvatochromic effect is noted in the fluorescence spectra of Nile Red based carbon dots in different solvents.

Three-mode optical thermometer based on Ca3LiMgV3O12:Sm3+ phosphors

A series of Ca3-xLiMgV3O12:xSm3+ (CLMV:Sm3+) phosphors were elaborated to provide new optical temperature sensing materials. Their structures, morphologies, and luminescent properties were comprehensively explored. The energy transfer from VO43− to Sm3+ was illustrated using luminescent spectra and luminescent decay curves. The different temperature dependent emission and excitation characters of VO43− group and 4f-4f transition of Sm3+ were used to design a three-mode optical temperature sensor. Temperature dependent fluorescence intensity ratio (FIR) value of I(Sm3+) and I(VO43−), Commission International de L'Eclairage (CIE) coordinate, and excitation intensity ratio (EIR) value of I383nm/I405nm in excitation spectra are the three sensing modes. The maximum value of absolute sensitivity (SA) and relative sensitivity (SR) in FIR mode are 9.11 %K−1 at 513 K and 1.99 %K−1 at 357 K, respectively. And SR is bigger than 1.21 %K−1 between 303 and 513 K, which is superior to that of thermometry based on Er3+ doped upconversion phosphors. The maximum SR in EIR mode is 1.39 %K−1 at 393 K. Our results indicate that CLMV:Sm3+ phosphors might have potential application as optical thermometry with self-reference character.

Triplet-Triplet Annihilation via the Triplet Channel in Crystalline 9,10-Diphenylanthracene.

Delayed fluorescence resulting from triplet-triplet annihilation in crystalline 9,10-diphenylanthracene was observed by means of steady-state fluorescence measurements under magnetic fields of ≤10 T. At five specific magnetic fields, four peaks and one dip in the magnetic field dependence of fluorescence intensity were observed, proving that exchange-coupled triplet pairs were generated in the course of triplet-triplet annihilation. The dip was in the opposite direction predicted for singlet channel triplet-triplet annihilation. Further analysis using the stochastic Liouville equation confirmed that the closest exchange-coupled triplet pair in crystalline 9,10-diphenylanthracene is quenched via both triplet channel and singlet channel triplet-triplet annihilation.

Photoluminescence effects and probing phase transition of Sm3+-doped Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3 phosphor prepared by hydrothermal method

A series of [(Ba(1-0.3y)Ca0.3y)1-xSmx][Ti(0.8+0.2y)Hf(0.2-0.2y)]O3 (Sm3+-doped (1-y)Ba(Ti0.8Hf0.2)O3-y(Ba0.7Ca0.3)TiO3, abbreviated as Sm3+-doped BCTH, or (1-y)BHT-yBCT:xSm3+, x = 0.0005–0.03, y = 0.2–0.7, y representing the mole fraction of (Ba0.7Ca0.3)TiO3) nano phosphors were prepared by a hydrothermal method. The Sm3+ ions doping amount and triple-point morphotropic phase boundary (TMPB) composition dependent photoluminescence properties were systematically investigated. The hydrothermal synthesized powders present rather pure pseudo-cubic perovskite phase structure at room temperature and locate on the rhombohedral side of MPB. Under the excitation of 409 nm light, the powders exhibit dominant orange-red emission peaks with characteristic emission of the Sm3+ ions at around 564 nm, 596 nm, 644 nm, and 703 nm, relating to the transitions of 4G5/2 → 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The BHT-0.5BCT:0.005Sm3+ powder exhibits optimal emission in these Sm3+-doped BCTH powders. Furthermore, the phase transition temperature can be characterized by the multi-feature changes of the temperature dependent fluorescence intensity.

L-Tryptophan Aqueous Systems at Low Concentrations: Interconnection between Self-Organization, Fluorescent and Physicochemical Properties, and Action on Hydrobionts.

As shown by fluorescence monitoring of dissolved organic matter, amino acid L-Trp can be present in natural water. The consequences of the presence of L-Trp at low concentrations in surface water systems are not yet established for hydrobionts. Studying the physicochemical patterns, as well as their relationships to the bioeffects of L-Trp solutions in the low concentration range, can provide new and important information regarding the unknown effects of L-Trp. The self-organization, physicochemical properties, fluorescence, UV absorption, and action of L-Trp solutions on Paramecium caudatum infusoria, Chlorella vulgaris algae were studied in the calculated concentrations range of 1 × 10−20–1 × 10−2 mol/L. The relationship between these phenomena was established using the certified procedures for monitoring the toxicity of natural water and wastewater. It was shown for the first time that aqueous solutions of L-Trp are dispersed systems in which the dispersed phase (nanoassociates) undergoes a rearrangement with dilution, accompanied by coherent changes in the nanoassociates’ parameters and the properties of systems. The non-monotonic concentration dependence of fluorescence intensity (λex at 225 nm, λem at 340 nm) is in good agreement with the data on the nanoassociates’ parameters, as well as with both the physicochemical properties of the systems and their bioassay results.

Efficient UV-visible emission enabled by 532 nm CW excitation in an Ho3+-doped ZBLAN fiber.

Rare-earth-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fibers have evolved to become promising candidates for efficient UV-visible emission because of their low phonon energy and low optical losses, as well as their well-defined absorption bands. We investigate the efficient emission of UV-visible light in a low-concentration (0.1 mol%) Ho3+-doped ZBLAN fiber excited by a 532 nm CW laser. In addition to the direct populating of the thermalized 5F4+5S2 levels by ground-state absorption, the upconversion processes responsible for UV-visible emission from the higher emitting levels, 3P1+3D3, 3K7+5G4, 5G5, and 5F3, of the Ho3+ ions are examined using excited-state absorption. The dependence of UV-visible fluorescence intensity on launched green pump power is experimentally determined, confirming the one-photon and two-photon characters of the observed processes. We theoretically investigate the excitation power dependence of the population density for nine Ho3+ levels based on a rate equation model. This qualitative model has shown a good agreement with the measured power dependence of UV-visible emission. Moreover, the emission cross-sections for blue, green, red, and deep-red light in the visible region are measured using the Füchtbauer-Ladenburg method and corroborated by McCumber theory, and the corresponding gain coefficients are derived. We propose an alternative approach to achieve efficient UV-visible emission in an Ho3+-doped ZBLAN fiber using a cost-effective, high-brightness 532 nm laser.

HSA-Lys-161 covalent bound fluorescent dye for in vivo blood drug dynamic imaging and tumor mapping.

The specific combination of human serum albumin and fluorescent dye will endow superior performance to a coupled fluorescent platform for in vivo fluorescence labeling. In this study, we found that lysine-161 in human serum albumin is a covalent binding site and could spontaneously bind a ketone skeleton quinoxaline–coumarin fluorescent dye with a specific turn-on fluorescence signal for the first time. Supported by the abundant drug binding domains in human serum albumin, drugs such as ibuprofen, warfarin and clopidogrel could interact with the fluorescent dye labeled human serum albumin to feature a substantial enhancement in fluorescence intensity (6.6-fold for ibuprofen, 4.5-fold for warfarin and 5-fold for clopidogrel). The drug concentration dependent fluorescence intensity amplification realized real-time, in situ blood drug concentration monitoring in mice, utilizing ibuprofen as a model drug. The non-invasive method avoided continuous blood sample collection, which fundamentally causes suffering and consumption of experimental animals in the study of pharmacokinetics. At the same time, the coupled fluorescent probe can be efficiently enriched in tumors in mice which could map a tumor with a high-contrast red fluorescence signal and could hold great potential in clinical tumor marking and surgical resection.

Effect of pH on Fluorescence Spectra of Coumarin Derivatives.

Colourless crystalline solid coumarin with a bitter taste and sweet vanilla-like odor mostly acts as chemical protection against predators in plants. Anticoagulants (blood thinners), anti-fungicidal, anti-tumor and anti-inflammatory properties of coumarin are all used to treat skin diseases. Because of internal charge transfer (ICT), coumarin molecules displayed a solvatochromic effect in various solvents of varying polarity. The emission wavelength dependent fluorescence intensity was also affected by pH.

Hot-band absorption of indocyanine green for advanced anti-stokes fluorescence bioimaging

Bright anti-Stokes fluorescence (ASF) in the first near-infrared spectral region (NIR-I, 800 nm–900 nm) under the excitation of a 915 nm continuous wave (CW) laser, is observed in Indocyanine Green (ICG), a dye approved by the Food and Drug Administration for clinical use. The dependence of fluorescence intensity on excitation light power and temperature, together with fluorescence lifetime measurement, establish this ASF to be originated from absorption from a thermally excited vibrational level (hot-band absorption), as shown in our experiments, which is stronger than the upconversion fluorescence from widely-used rare-earth ion doped nanoparticles. To test the utility of this ASF NIR-I probe for advanced bioimaging, we successively apply it for biothermal sensing, cerebral blood vessel tomography and blood stream velocimetry. Moreover, in combination with L1057 nanoparticles, which absorb the ASF of ICG and emit beyond 1100 nm, these two probes generate multi-mode images in two fluorescent channels under the excitation of a single 915 nm CW laser. One channel is used to monitor two overlapping organs, urinary system & blood vessel of a live mouse, while the other shows urinary system only. Using in intraoperative real-time monitoring, such multi-mode imaging method can be beneficial for visual guiding in anatomy of the urinary system to avoid any accidental injury to the surrounding blood vessels during surgery.

Kanamycin-Mediated Conformational Dynamics of Escherichia coli Outer Membrane Protein TolC

TolC is a member of the outer membrane efflux proteins (OEPs) family and acts as an exit duct to export proteins, antibiotics, and substrate molecules across the Escherichia coli cell membrane. Export of these molecules is evidenced to be brought about through the reversible interactions and binding of substrate-specific drug molecules or antibiotics with TolC and by being open for transport, which afterward leads to cross-resistance. Hence, the binding of kanamycin with TolC was monitored through molecular docking (MD), the structural fluctuations and conformational changes to the atomic level. The results were further supported from the steady-state fluorescence binding and isothermal titration calorimetry (ITC) studies. Binding of kanamycin with TolC resulted in a concentration dependent fluorescence intensity quenching with 7 nm blue shift. ITC binding data maintains a single binding site endothermic energetic curve with binding parameters indicating an entropy driven binding process. The confirmational changes resulting from this binding were monitored by a circular dichroism (CD) study, and the results showed insignificant changes in the α-helix and β-sheets secondary structure contents, but the tertiary structure shows inclusive changes in the presence of kanamycin. The experimental data substaintially correlates the RMSD, R g, and RMSF results. The resulting conformational changes of the TolC-kanamycin complexation was stabilized through H-bonding and other interactions.

Modulating the magnetic-optical properties of Zn1−xCoxO nanocrystals with x-content

In this study, magnetic-optical properties of Zn1−xCoxO NCs were modulated with x-content. The optical, structural, morphological, and magnetic properties were investigated by optical absorption (OA), fluorescence (FL), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and electronic paramagnetic resonance (EPR). The XRD and Raman results confirm the growth of Zn1−xCoxO NCs, with x greater than 1.0 having occurred for the formation of the nanocomposite (Co-doped ZnO/ZnCo2O4). The formation of the nanocomposite allows new and exciting optical and magnetic properties. SEM images show inhibition in ZnO nanorod growth with Co-content and formation of ZnCo2O4 NCs. OA and FL spectra have changed with x-content in Zn1−xCoxO NCs. These changes are strongly related to the symmetric environment of the Co2+ ions within ZnO NCs and the formation of ZnCo2O4 NCs. A linear dependence of FL intensity was observed with the x-content in the red-green region. The symmetric environment and the nanocomposite formation also alter the magnetic properties confirmed by EPR. Therefore, Zn1−xCoxO NCs can be a material platform suitable for photonic devices, magnetic-optical devices, or spintronics.

Design of opposite thermal behaviors in Tm3+/Eu3+ co-doped YVO4 for high-sensitivity optical thermometry.

Temperature-induced redshift of the V-O charge transfer band edge and the temperature quenching effect were combined for designing ratiometric optical thermometry. Following this approach, opposite thermal behaviors of Tm3+ and Eu3+ emissions were realized in the range of 300 to 380 K in Tm3+/Eu3+ co-doped YVO4. Applying the temperature dependent fluorescence intensity ratio of Eu3+ to Tm3+ as temperature readout, the maximal relative sensitivity reaches up to 4.6%K-1 around 330 K. This result makes our proposed strategy an excellent candidate for developing high-sensitivity optical thermometry.

Fluorescence characteristics of aqueous dispersed systems of succinic acid as potential markers of their self-organization and bioeffects in low concentration range

Abstract The issue of protecting aquatic ecosystems from biologically active compounds (BACs) such as pesticides and pharmaceuticals detected in aquatic environments at low concentrations has become urgent. Presently, literature provides much information about BACs that at low concentrations cause significant damage to hydrobionts, but a physicochemical explanation for these phenomena has appeared only relatively recently. Experimental findings have shown that diluted aqueous solutions of BACs are self-organized disperse systems, whose disperse phase (nanoassociates) rearranges upon dilution, which is accompanied by nonmonotonous changes in the physicochemical and biological properties of the system. This work introduces the study of fluorescence and UV absorption of aqueous diluted systems of a biogenic succinic acid (SA), used as an antihypoxic and antioxidant pharmaceutical. It is shown for the first time that the fluorescence spectra ( λ e x at 225 nm) of SA systems are informative at the calculated concentrations range from 1 ⋅ 10−17 to 1 ⋅ 10−5 M. The nonmonotonous concentration dependence of fluorescence intensity ( λ e x at 225 nm, λ e m at 350 nm) is in good agreement with the data on nanoassociates’ size, as well as with both the physicochemical properties of SA systems and their biotesting results, which were obtained using the certified procedures for monitoring the toxicity of natural waters and wastewater. The observed coherence between the fluorescence intensity of SA systems and the nanoassociates’ size allows for the conclusion that it may be possible to consider fluorescence as a potential marker of self-organization and bioeffects of diluted aqueous BACs systems.

Photochemistry of nabumetone in aqueous solution of sodium dodecyl sulfate (SDS) micelles

The photochemistry, solubility and distribution between two phases of nabumetone (NB) in aqueous solution of sodium dodecyl sulfate (SDS) micelles were studied. The solubility (SNB) of NB was monitored using steady-state UV–Vis absorption spectroscopy. The linear relationship of SNB to SDS concentration ([SDS]) gave the large value of partition coefficient, P (logP = 3.5), for NB distribution between the aggregate and the water phase showing the localization of NB in the micellar phase. NB fluorescence (FL) quantum yield increases with [SDS] from 0.03 in water to 0.056 at 0.2 M [SDS]. The dependence of FL intensity at 355 nm (F335) on [SDS] is bell-shaped. The plot of initial F335 increase with [SDS] in the range 0–0.05 M gave the expected value of the critical micelle concentration (cmc = 7.9 mM). Further increase of [SDS] resulted in 10% decrease of F335 demonstrating the variation of the micellar structure. Small-Angle Neutron Scattering (SANS) and refractometry confirmed this variation. The NB in SDS was protected against photodegradation. High Performance Liquid Chromatography/Mass Spectrometry (HPLC/MS) detected 2-(but-2-en-1-yl)-6-methoxynaphthalene as NB final photoproducts in SDS solution which was not found in homogeneous media. The hydrated electron localized in water phase, NB radical cation and NB triplet excited state both localized in the micellar phase were observed by laser flash photolysis of NB in micellar solution. The decay kinetics of these intermediates was different with respect to that in the homogeneous media. The reactivity of NB in SDS micellar environment compared to the homogeneous media is under the discussion.

Facile synthesis and photoluminescence performance of Er3+-activated BiOF sub-micro particles for ratiometric thermometers

A series of the Er3+-activated BiOF sub-micro particles were successfully synthesized by means of a facile technology of solid-state reaction route so as to explore new thermometric materials. The phase structure and microstructure information of the designed samples were verified by the X-ray diffraction, field-emission scanning electron microscope and transmission electron microscope. The whole sub-micro particles can emit bright green emission with high color purity of 79.3% when excited by 378 nm and the optimal doping concentration for the Er3+ ions in the BiOF host lattices was 7 mol%. Based on the calculation results, one knows that the concentration quenching mechanism was contributed by the electric dipole-dipole interaction and the critical distance between the Er3+ ions in the BiOF host lattice was 15.5 Å. Furthermore, the temperature dependent fluorescence intensity ratio of the green emissions arising from the thermally coupled levels (i.e., 2H11/2 and 4S3/2) was studied so as to explore the feasibility of the resultant sub-micro particles for optical thermometers. The maximum absolute and relative sensitivities of the designed nanoparticles were 0.0051 K-1 and 1.11% K−1, respectively, implying that the Er3+-activated BiOF sub-micro particles were promising candidates for ratiometric thermometers.

Diagnostics of non-carious lesions of dental hard tissues with the methods of optical spectroscopy and radiography

Objective: This work aims to use new spectroscopic and radiographic methods to study the dental hard tissue erosion and abfraction, as these lesions are actually quite difficult to be diagnosed in clinical practice. Material and Methods: This in vivo study was conducted on 60 patients with early erosion and 60 patients with abfraction at the cervical area by means of laser-induced fluorescence (LIF) and multilayer spiral computed tomography (MSCT). Results: In comparative dental hard tissues studies LIF spectra from intact and affected areas, it was noted multidirectional fluorescence intensity dependence between areas affected by abfraction and intact areas. MSCT technique allowed assessing the degree of damaged areas, especially at deeper stages. Conclusion: Although LIF and MSCT methods presented limitations, it was shown their effectiveness in the diagnosis of abfraction and erosion by detecting changes in the morphological structure as well as in the chemical and mineral composition of affected dental hard tissues. So LIF and MSCT methods can be successfully used in order to develop new medical devices which will provide most accurate clinical diagnose of different stages of dental erosion and abfraction.KEYWORDSFluorescence spectroscopy; Spiral computed tomography; Tooth demineralization; Tooth erosion.

Ground‐ and Excited‐State Symmetry Breaking and Solvatofluorochromism in Centrosymmetric Pyrrolo[3,2‐b]pyrroles Possessing two Nitro Groups

AbstractSix centrosymmetric pyrrolo[3,2‐b]pyrroles possessing either two nitro or two CF3SO2 strong electron‐withdrawing groups have been synthesized in a straightforward manner from simple building blocks and their one and two‐photon properties investigated. Although two‐photon absorption maxima clearly correspond to the S0→S2 transition, there is always a considerable shoulder at the region related to the S0→S1 transition. This fact clearly points to a small degree of symmetry breaking in the ground state which becomes more prevalent in the excited state. The systems showing the strongest excited‐state symmetry breaking have also been identified by first principles calculations. Both experimental data and theoretical calculations (performed with time‐dependent density functional theory) have revealed that changing the degree of conjugation between the nitro−aryl substituents and the core enables fine‐tuning of not only emission wavelengths but also the solvent dependent fluorescence intensity. Although there is no charge‐transfer between electron‐withdrawing 4‐cyanophenyl substituents located on nitrogen atoms and the core, nevertheless, their presence modifies the absorption and emission maxima. These groups also enable a record high fluorescence quantum yield in toluene (0.97) to be reached. By probing ground‐state symmetry by two‐photon absorption and excited‐state symmetry by solvatofluorochromism, we are able to obtain insight regarding the pathway of the molecule during and after the electronic transition.