Fluorescence Lifetime Spectroscopy Research Articles

Bi-Doped and Bi Nanoparticles Loaded CeO2 Derived from Ce-MOF for Photocatalytic Degradation of Formaldehyde Gas and Tetracycline Hydrochloride.

Bi/CeO2 (BC-x) photocatalysts are successfully prepared by solvothermal loading Bi nanoparticles and Bi-doped CeO2 derived by Ce-MOF (Ce-BTC). Formaldehyde gas (HCHO) and tetracycline hydrochloride (HTC) are used to evaluate the photocatalytic activity of the synthesized Bi/CeO2. For BC-1000 photocatalyst, the degradation of HTC by 420nm < λ < 780nm light reaches 91.89% for 90min, and HCHO by 350nm < λ < 780nm light reaches 94.66% for 120min. The photocatalytic cycle experiments prove that BC-1000 has good cyclic stability and repeatability. The results of photoluminescence spectra, fluorescence lifetime, photocurrent response, and electrochemical impedance spectroscopy showed that the SPR (Surface Plasmon Resonance) effect of Bi nanoparticles acted as a bridge and promoted electron transfer and enhanced the response-ability of Bi/CeO2 to visible light. Bi-doping produced more oxygen vacancies to provide adsorption sites for adsorbing oxygen and generated more ·O2 - thus promoting photocatalytic reactions. The mechanism of photocatalytic degradation is analyzed in detail utilizing active free radical capture experiments and electron paramagnetic resonance (EPR) characterization. The experimental results indicate that ·O2 - and h+ active free radicals significantly promote the degradation of pollutants.

Charge transfer induced linear and nonlinear optical properties in polypyrrole/ZnO@MoS2 ternary composites

Polymer-based ternary nanocomposites with tunable optical properties are the key components for optoelectronics applications. Here, we demonstrate the linear and nonlinear optical properties of polypyrrole (PPy) and its ternary composites with different concentrations of the MoS2–ZnO core–shell (ZnO@MoS2) heterostructure. The interesting observation of multiple excitons and their transportation through the interface of PPy and ZnO@MoS2 by using photoluminescence and fluorescence lifetime spectroscopy was studied. Furthermore, the third-order nonlinear optical properties of all samples were also measured by employing the z-scan technique at an excitation wavelength of 532 nm. The reverse saturable absorption of pure PPy was switched to saturable absorption after the addition of ZnO@MoS2 at the uniform linear transmittance. These ternary composites with good nonlinear responses provide an option for the development of high-performance nonlinear optical devices and open a new path for the future development of ternary systems in the optical fields.

Synthesis of a water-stable CsPbBr3 perovskite for selective detection of mercury ion in water.

By using the method of low-temperature crystallization, CsPbBr3 perovskite nanocrystals (PNCs) coated with trifluoroacetyl lysine (Tfa-Lys) and oleamine (Olam) were synthesized in aqueous solution. The structure of the CsPbBr3 PNCs was characterized by many methods, such as ultraviolet (UV)-visible absorption spectrophotometer, fluorescence spectrophotometer, transmission electron microscopy (TEM), and X-ray diffraction (XRD) pattern. The fluorescence emission of the CsPbBr3 PNCs is stable in water for about 1 day at room temperature. It was also found that the fluorescence of the PNCs could be obviously and selectively quenched after the addition of mercury ion (Hg2+ ), allowing a visual detection of Hg2+ by the naked eye under UV light illumination. The fluorescence quenching rate (I0 /I) has a good linear relationship with the addition of Hg2+ in the concentration range 0.075 to 1.5 mg/L, with a correlation coefficient (R2 ) of 0.997, and limit of detection of 0.046 mg/L. The fluorescence quenching mechanism of the PNCs was determined by the fluorescence lifetime and X-ray photoelectron spectroscopy (XPS) of the PNCs. Overall, the synthesis method for CsPbBr3 PNCs is simple and rapid, and the as-prepared PNCs are stable in water that could be conveniently used for selective detection of Hg2+ in the water environment.

Rational Design of Covalent Multiheme Cytochrome‐Carbon Dot Biohybrids for Photoinduced Electron Transfer

AbstractBiohybrid systems can combine inorganic light‐harvesting materials and whole‐cell biocatalysts to utilize solar energy for the production of chemicals and fuels. Whole‐cell biocatalysts have an intrinsic self‐repair ability and are able to produce a wide variety of multicarbon chemicals in a sustainable way with metabolic engineering. Current whole‐cell biohybrid systems have a yet undefined electron transfer pathway between the light‐absorber and metabolic enzymes, limiting rational design. To enable engineering of efficient electron transfer pathways, covalent biohybrids consisting of graphitic nitrogen doped carbon dots (g‐N‐CDs) and the outer‐membrane decaheme protein, MtrC from Shewanella oneidensis MR‐1 are developed. MtrC is a subunit of the MtrCAB protein complex, which provides a direct conduit for bidirectional electron exchange across the bacterial outer membrane. The g‐N‐CDs are functionalized with a maleimide moiety by either carbodiimide chemistry or acyl chloride activation and coupled to a surface‐exposed cysteine of a Y657C MtrC mutant. MtrC∼g‐N‐CD biohybrids are characterized by native and denaturing gel electrophoresis, chromatography, microscopy, and fluorescence lifetime spectroscopy. In the presence of a sacrificial electron donor, visible light irradiation of the MtrC∼g‐N‐CD biohybrids results in reduced MtrC. The biohybrids may find application in photoinduced transmembrane electron transfer in S. oneidensis MR‐1 for chemical synthesis in the future.

Achieving chip-matched high purity red emission by Bi3+ sensitization in Ca3MgTiGe3O12:Pr3+

Phosphor-converted light emitting diodes (pc-LEDs) are essential for current lighting and display areas because of their unique properties of being uncomplicated, durable and economical. In previous studies, Pr3+ doped red-emitting phosphors have attracted enormous research interest due to their high color purity. However, their photoluminescence excitation (PLE) spectra are always hard to be combined with LED chips. This mismatch is a great obstacle to achieve Pr3+ phosphors utilizing in LED devices. Here, to circumvent this issue, Pr3+-doped Ca3MgTiGe3O12 (CMTG) red-emitting phosphor was optimized with PLE band shifting from 330 nm to 360 nm after tuning with Bi3+ co-doping based on the structure and phosphorescence properties. The chip-matched excitation makes it a good candidate for white LEDs (wLEDs) fabrication to improve the output quality of device. Meanwhile, the high color purity of 93.02 % was obtained, which is conducive to widening the color gamut of backlight display applications. The photoluminescence (PL) spectra, fluorescence lifetime, and X-ray photoelectron spectroscopy (XPS) analysis were employed and discussed in detail to explain the role of Bi3+ played in the system. Finally, wLEDs were fabricated with CMTG:Pr3+, Bi3+, showing a high color rendering index (Ra) of 94.4. And the color gamut covers ∼80 % of the National Television System Committee (NTSC) standard, suggesting great potential for applications of wLEDs and backlight display.

Stability of retinol in liposomes as measured by fluorescence lifetime spectroscopy and FLIM

Retinol shows complex photophysical properties that make it potentially useful as an exogenous or endogenous probe of membrane microenvironment, but it has not been fully explored. In this study, we use bulk fluorescence lifetime measurements and fluorescence lifetime imaging microscopy (FLIM) to examine the stability of retinol in phosphatidylcholine (PC) multilamellar and unilamellar vesicles with and without cholesterol. We find that both light and exposure to ambient temperature and oxygen contribute to retinol degradation, with the addition of an antioxidant such as butylated hydroxytoluene (BHT) essential to provide stability, especially in the absence of cholesterol. With exposure to ultraviolet light to excite its native fluorescence, retinol degrades rapidly and can photosensitize vesicles. Degradation can be measured by a decrease in fluorescence lifetime. In POPC vesicles without cholesterol, BHT leads to initially higher lifetimes compared with no BHT, but it increases the rate of photodegradation. The presence of 10 mol % cholesterol protects against this effect, and vesicles with 20 mol % cholesterol show longer lifetimes without BHT under all conditions. Because of its environmental sensitivity, retinol is interesting as a FLIM probe, but careful controls are needed to avoid degradation, and additional work is needed to optimize liposomes for food and cosmetic applications.

Fluorescent folic acid-capped copper nanoclusters for the determination of rifampicin based on inner filter effect

Development of excellent sensors to determine trace concentrations of rifampicin is of intense importance for medicine analysis and human health. Herein, a facile and green fluorescent probe was established for the determination of rifampicin by using folic acid protected copper nanoclusters (FA-Cu NCs). Many characterization methods were applied for the analysis of the as-prepared FA-Cu NCs including UV–visible absorption spectra, fluorescence spectra, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), fluorescence lifetime and X-ray photoelectron spectroscopy (XPS). The TEM image suggested that the as-prepared FA-Cu NCs were highly dispersed. The as-synthesized FA-Cu NCs emerged blue fluorescence under UV light and demonstrated maximum emission wavelength at 446 nm under the maximum excitation wavelength of 358 nm. After the addition of rifampicin, the FL intensities of FA-Cu NCs were uncommonly quenched. The related experimental data intimated that the quenching mechanisms were assumed to the inner filter effect (IFE) and static quenching. The as-proposed probe platform displayed an obvious linear relationship with rifampicin concentrations varying from 0.5 to 100 µM, and the corresponding detection limit (LOD) was 0.073 µM (S/N = 3). Finally, the as-established detection platform was successfully employed to analyze trace concentrations of rifampicin in real samples.

Multiscale Dynamics of Lipid Vesicles in Polymeric Microenvironment.

Understanding dynamic and complex interaction of biological membranes with extracellular matrices plays a crucial role in controlling a variety of cell behavior and functions, from cell adhesion and growth to signaling and differentiation. Tremendous interest in tissue engineering has made it possible to design polymeric scaffolds mimicking the topology and mechanical properties of the native extracellular microenvironment; however, a fundamental question remains unanswered: that is, how the viscoelastic extracellular environment modifies the hierarchical dynamics of lipid membranes. In this work, we used aqueous solutions of poly(ethylene glycol) (PEG) with different molecular weights to mimic the viscous medium of cells and nearly monodisperse unilamellar DMPC/DMPG liposomes as a membrane model. Using small-angle X-ray scattering (SAXS), dynamic light scattering, temperature-modulated differential scanning calorimetry, bulk rheology, and fluorescence lifetime spectroscopy, we investigated the structural phase map and multiscale dynamics of the liposome–polymer mixtures. The results suggest an unprecedented dynamic coupling between polymer chains and phospholipid bilayers at different length/time scales. The microviscosity of the lipid bilayers is directly influenced by the relaxation of the whole chain, resulting in accelerated dynamics of lipids within the bilayers in the case of short chains compared to the polymer-free liposome case. At the macroscopic level, the gel-to-fluid transition of the bilayers results in a remarkable thermal-stiffening behavior of polymer–liposome solutions that can be modified by the concentration of the liposomes and the polymer chain length.

Fluorescence lifetime imaging microscopy reveals sodium pump dimers in live cells

The sodium-potassium ATPase (Na/K-ATPase, NKA) establishes ion gradients that facilitate many physiological functions including action potentials and secondary transport processes. NKA comprises a catalytic subunit (alpha) that interacts closely with an essential subunit (beta) and regulatory transmembrane micropeptides called FXYD proteins. In the heart, a key modulatory partner is the FXYD protein phospholemman (PLM, FXYD1), but the stoichiometry of the alpha–beta–PLM regulatory complex is unknown. Here, we used fluorescence lifetime imaging and spectroscopy to investigate the structure, stoichiometry, and affinity of the NKA-regulatory complex. We observed a concentration-dependent binding of the subunits of NKA–PLM regulatory complex, with avid association of the alpha subunit with the essential beta subunit as well as lower affinity alpha–alpha and alpha–PLM interactions. These data provide the first evidence that, in intact live cells, the regulatory complex is composed of two alpha subunits associated with two beta subunits, decorated with two PLM regulatory subunits. Docking and molecular dynamics (MD) simulations generated a structural model of the complex that is consistent with our experimental observations. We propose that alpha–alpha subunit interactions support conformational coupling of the catalytic subunits, which may enhance NKA turnover rate. These observations provide insight into the pathophysiology of heart failure, wherein low NKA expression may be insufficient to support formation of the complete regulatory complex with the stoichiometry (alpha-beta-PLM)2.

Fluorescence Microscopy Methods for the Analysis and Characterization of Lignin.

Lignin is one of the most studied and analyzed materials due to its importance in cell structure and in lignocellulosic biomass. Because lignin exhibits autofluorescence, methods have been developed that allow it to be analyzed and characterized directly in plant tissue and in samples of lignocellulose fibers. Compared to destructive and costly analytical techniques, fluorescence microscopy presents suitable alternatives for the analysis of lignin autofluorescence. Therefore, this review article analyzes the different methods that exist and that have focused specifically on the study of lignin because with the revised methods, lignin is characterized efficiently and in a short time. The existing qualitative methods are Epifluorescence and Confocal Laser Scanning Microscopy; however, other semi-qualitative methods have been developed that allow fluorescence measurements and to quantify the differences in the structural composition of lignin. The methods are fluorescence lifetime spectroscopy, two-photon microscopy, Föster resonance energy transfer, fluorescence recovery after photobleaching, total internal reflection fluorescence, and stimulated emission depletion. With these methods, it is possible to analyze the transport and polymerization of lignin monomers, distribution of lignin of the syringyl or guaiacyl type in the tissues of various plant species, and changes in the degradation of wood by pulping and biopulping treatments as well as identify the purity of cellulose nanofibers though lignocellulosic biomass.

Fluorescence Lifetime and Cross-correlation Spectroscopy for Observing Membrane Fusion of Liposome Models Containing Synaptic Proteins.

Watching events of membrane fusion in real time and distinguishing between intermediate steps of these events is useful for mechanistic insights but at the same time a challenging task. In this chapter, we describe how to use fluorescence cross-correlation spectroscopy and Förster-resonance energy transfer to resolve the tethering and fusion of membranes by SNARE proteins (syntaxin-1, SNAP-25, and synaptobrevin-2) as an example. The given protocols can easily be adapted to other membrane proteins to investigate their ability to tether or even fuse vesicular membrane.

Tunable Fluorescein-Encapsulated Zeolitic Imidazolate Framework-8 Nanoparticles for Solid-State Lighting

A series of fluorescein-encapsulated zeolitic imidazolate framework-8 (fluorescein@ZIF-8) luminescent nanoparticles with a scalable guest loading has been fabricated and characterized. The successful encapsulation of the organic dye (fluorescein) is supported by both experimental evidence and theoretical simulations. The measured optical band gap is found to be comparable with the computed values of a hypothetical guest-host system. Isolated monomers and aggregates species of fluorescein confined in ZIF-8 nanocrystals have been systematically investigated through fluorescence lifetime spectroscopy. The quantum yield (QY) of the obtained solid-state materials is particularly high (QY~98%), especially when the concentration of the fluorescein guest is low. Combining a blue LED chip and a thin photoactive film of fluorescein@ZIF-8, we demonstrate a device with good optical tunability for multicolor and white light emissions. Additionally, we show that the fluorescein@ZIF-8 nanoparticles exhibit an improved photostability due to the shielding effect conferred by the nanoconfinement of host framework, making them promising candidates for practical applications such as solid-state lighting, photonics, and optical communications.

Molecular and Spectroscopic Characterization of Green and Red Cyanine Fluorophores from the Alexa Fluor and AF Series.

The front cover artwork was provided by Gabriel Moya, a PhD student in the Cordes lab (LMU Biocenter Munich, Germany). The cover image shows an artistic impression of the chemical structures of two fluorophores investigated in the paper. Read the full text of the Article at 10.1002/cphc.202000935.

Distinguishing between coherent and incoherent signals in excitation-emission spectroscopy.

The separation of incoherent emission signals from coherent light scattering often poses a challenge in (time-resolved) microscopy or excitation-emission spectroscopy. While in spectro-microscopy with narrowband excitation this is commonly overcome using spectral filtering, it is less straightforward when using broadband Fourier-transform techniques that are now becoming commonplace in, e.g., single molecule or ultrafast nonlinear spectroscopy. Here we show that such a separation is readily achieved using highly stable common-path interferometers for both excitation and detection. The approach is demonstrated for suppression of scattering from flavin adenine dinucleotide (FAD) and weakly emissive cryptochrome 4 (Cry4) protein samples. We expect that the approach will be beneficial, e.g., for fluorescence lifetime or Raman-based imaging and spectroscopy of various samples, including single quantum emitters.

Highly Stable Acid-Induced Emission-Enhancing Cd-MOFs: Synthesis, Characterization, and Detection of Glutamic Acid in Water and Fe Ions in Acid

Two novel 3D fluorescent metal-organic frameworks (MOFs), [Cd(L)(bbibp)]n (1) and [Cd(L)(bbibp)0.5]n (2), where H2L = 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoic acid and bbibp = 4,4'-bis(benzoimidaz-1-yl)biphenyl, were acquired through a conventional method and characterized via IR spectra, single-crystal X-ray diffraction, elemental analysis, thermogravimetric analysis, powder X-ray diffraction (PXRD), scanning electron microscopy, N2 adsorption-desorption isotherms, and X-ray photoelectron spectroscopy (XPS). The crystal framework of Cd-MOF 1 remained stable in the range of pH = 1.0-12.0. Interestingly, the emission peak of 1 showed a red shift and exhibited a fluorescence turn-on effect in an acidic environment. X-ray diffraction measurement revealed that the crystal structure of 1 remained unchanged after immersion in a pH = 1.0 solution. In addition, Cd-MOFs 1 and 2 displayed fluorescent quenching to l-glutamic acid with high sensitivity and selectivity. Meanwhile, 1 showed high selectivity in recognizing Fe3+ under acidic conditions, which made 1 capable of detecting Fe3+ in acidic industrial wastewater. Finally, the fluorescent sensing mechanism was carefully studied by PXRD, transient fluorescence lifetime, XPS, and UV spectroscopy.

The density of surface ligands regulates the luminescence of thiolated gold nanoclusters and their metal ion response

The fascinating luminescence properties of gold nanoclusters (AuNCs) have drawn considerable research interests, and been widely harnessed for a wide range of applications. However, a fundamental understanding towards ligand density’s role in the luminescence properties of these ultrasmall AuNCs remains unclear yet. In this communication, through systematic investigation of surface chemistries of glutathione-protected AuNCs (GSH-AuNCs) with different density of GSH as well as other thiolates, it is discovered that the density of surface ligands can significantly regulate the luminescence properties of AuNCs. Fluorescence lifetime spectroscopy and X-ray photoelectron spectroscopy showed that AuNCs with a higher density of electron-rich ligands facilitate their luminescence generation. Moreover, differences in the surface coverage of AuNCs can also affect their interactions with foreign species, as illustrated by significantly different fluorescence quenching capability of GSH-AuNCs with different ligand density towards Hg2+. This study provides new insight into the intriguing luminescence properties of metal NCs, which is hoped to stimulate further research on the design of metal NCs with strong luminescence and sensitive/specific responses for promising optoelectronic, sensing and imaging applications.

Negative Interdomain Coupling of Dystrophin Spectrin Repeats

Spectrin repeat domains are a highly conserved biological motif found in many human structural proteins. Dystrophin contains 24 tandem spectrin repeats which provide structural support through mediating interactions between intracellular actin filaments and the extracellular matrix. However, the molecular mechanism by which dystrophin provides this support is unknown. Understanding this underlying structure/function relationship is important because mutations in dystrophin directly cause muscular dystrophy. Thus far, the following constructs have been expressed in E. coli, purified using chromatography, and thermodynamically characterized: S17, S17-18, S17-19. Parameters were determined through globally fitting thermal denaturation signals from Fluorescence Spectroscopy (FS), Circular Dichroism (CD), and Fluorescence Lifetime Spectroscopy (FLT) to a two-state model of unfolding. Fits were constrained using ΔCp values determined using Differential Scanning Calorimetry (DSC). This parameterization then allowed for determination of the free energy of stability (ΔGunfolding) of each construct. Results indicate that the ΔGunfolding of S17 is nearly double that of S17-19. This pronounced non-additivity indicates that tandem spectrin repeats mutually destabilize each other, termed negative coupling. Additionally, the comparison of Electron Paramagnetic Resonance (EPR) spectra of S17 and S17-19 indicate that the trimer exhibits greater local confirmational flexibility, consistent with decreased stability. To further test this negative coupling hypothesis, we are purifying S19 for thermodynamic characterization. This will allow for the comparison of the sum of S19 and S17-18's ΔGunfolding values with that of the trimer, helping further reveal the energetic and structural basis of dystrophin's mechanism.

Photoluminescence enhancement of Gd2Zr2O7:Eu3+ red phosphor sensitized by co-doped Al3+ ions

The exploration of new red phosphors is important for the development of white light-emitting diodes (w-LEDs), as existing red phosphors exhibit low efficiency and low performance. This work aims to enhance the photoluminescence characteristics of a red-emitting Gd2Zr2O7:Eu3+ phosphor by co-doping with Al3+. Eu3+ single-doped and Eu3+ and Al3+ co-doped Gd2Zr2O7 nanophosphors that could be efficiently pumped by commercial near-UV LED chips were prepared by a modified liquid–solid–solution phase-transfer method. X-ray diffraction data revealed that the synthesized phosphors were well crystallized with single-phase fluorite structure. Scanning electron microscopy images showed that the particle size ranges from 15 to 25 nm. In addition, the optical performance of the samples was characterized by fluorescence spectroscopy and lifetime spectroscopy. The effect of Al3+ on the luminescence performance of the Eu3+-doped Gd2Zr2O7 phosphor was studied in detail. The emission intensity of the Gd1.93Zr1·97O7:Eu3+0.07Al3+0.03 phosphor was found to be 620% stronger than that of the single-doped Eu3+ phosphor. These results unambiguously show that the Gd1.93Zr2-xO7:Eu3+0.07Al3+x phosphors are promising candidates for application in w-LEDs.

Er3+,Yb3+-doped oxyfluorotellurite glasses—Impact of temperature on spectroscopic properties and optical sensor qualities

Oxyfluorotellurite glasses co-doped with erbium (0.5%) and ytterbium (2%, 5%) were manufactured from high purity reagents at 840 °C in air. Differential thermal analysis was used to estimate the temperatures of glass transition and glass crystallization of 2% and 5%Yb co-doped glasses. The effect of Yb3+ co-doping on relaxation dynamics of erbium excited states was demonstrated by the means of excitation, emission and fluorescence lifetime spectroscopy. Up-conversion luminescence spectra were studied in a function of temperature in the 295–675 K range, yielding information on thermal quenching of the emission and a temperature sensing model based on 2H11/2–4I15/2 to 4S3/2–4I15/2 erbium fluorescence intensity ratio. Application potential of the investigated material in optical sensor thermometry was evaluated. Maximum absolute and relative sensitivities were established at 6.45 × 10−3 K−1 at T = 675 K and 0.46 %K−1 at T = 400 K, respectively.

Biological activities of biogenically synthesized fluorescent silver nanoparticles using Acanthospermum hispidum leaves extract

Silver nanoparticles (AgNPs) synthesized by an implicitly environmentally gracious route using Acanthospermum hispidum aqueous leaves extract at room temperature reported. This approach is facile, swift, cost-effective and stable for a long time, reproducible at room temperature and in an eco-friendly manner to obtain a self-assembly of AgNPs. These fabricated AgNPs were investigated by ultraviolet–visible spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscope with selected area electron diffraction, X-ray diffraction, Fourier transform Infrared spectroscopy, particle size, zeta potential, photoluminescence with fluorescence life-time spectroscopy and surface area with porosity studies of synthesized nanoparticles were analyzed by Brunauer–Emmett–Teller and Barrett–Joyner–Halenda curve. Besides, these AgNPs displayed antibacterial, antifungal antimycobacterial and antimalarial activity against some bacterial pathogens. From the outcomes obtained it is suggested that AgNPs could be used effectively in future nanobiotechnology and medical concerns.