Fluorescence Emission Efficiency Research Articles

Developing IR-780 as a Novel Matrix for Enhanced MALDI MS Imaging of Endogenous High-Molecular-Weight Lipids in Brain Tissues.

The matrix plays a prominent role in expanding the ability of matrix assisted laser desorption/ionization mass spectrometry (MALDI MS). However, on account of the unclarity of necessary properties of the matrix in MALDI MS, development of a new matrix is still in the exploratory stage and lacks systematic theoretical guidance. Meanwhile, most of the existing matrices are unable to simultaneously detect various high-molecular-weight (high-MW) lipids including (poly-)phosphoinositides, cardiolipins, and gangliosides. In this study, we have successfully screened and optimized the application of commercially available IR-780 as a novel matrix for simultaneously profiling and imaging high-MW lipids in brain tissues by MALDI MS for the first time. The properties of IR-780 related to the matrix of MALDI MS, mainly including the optical properties (UV absorption, fluorescence emission, and photothermal efficiency), proton affinity, collision cross-sections (CCSs), salt-tolerance ability, and homogeneity, were comprehensively characterized, which demonstrated that high photothermal ability and large CCSs might guarantee the superior performance of IR-780 as matrix for the analysis of high-MW lipids in biological samples. This work provided some references for the development of a novel matrix, and especially, the concept of CCS was first introduced as a parameter for the development of a matrix. In addition, the simultaneous identification and imaging of endogenous high-MW lipids in rat brain tissues subjected to traumatic brain injury were successfully performed.

Nitrogen and Phosphorus Effect on Sun-Induced Fluorescence and Gross Primary Productivity in Mediterranean Grassland

Sun-Induced fluorescence at 760 nm (F760) is increasingly being used to predict gross primary production (GPP) through light use efficiency (LUE) modeling, even though the mechanistic processes that link the two are not well understood. We analyzed the effect of nitrogen (N) and phosphorous (P) availability on the processes that link GPP and F760 in a Mediterranean grassland manipulated with nutrient addition. To do so, we used a combination of process-based modeling with Soil-Canopy Observation of Photosynthesis and Energy (SCOPE), and statistical analyses such as path modeling. With this study, we uncover the mechanisms that link the fertilization-driven changes in canopy nitrogen concentration (N%) to the observed changes in F760 and GPP. N addition changed plant community structure and increased canopy chlorophyll content, which jointly led to changes in photosynthetic active radiation (APAR), ultimately affecting both GPP and F760. Changes in the abundance of graminoids, (%graminoids) driven by N addition led to changes in structural properties of the canopy such as leaf angle distribution, that ultimately influenced observed F760 by controlling the escape probability of F760 (Fesc). In particular, we found a change in GPP–F760 relationship between the first and the second year of the experiment that was largely driven by the effect of plant type composition on Fesc, whose best predictor is %graminoids. The P addition led to a statistically significant increase on light use efficiency of fluorescence emission (LUEf), in particular in plots also with N addition, consistent with leaf level studies. The N addition induced changes in the biophysical properties of the canopy that led to a trade-off between surface temperature (Ts), which decreased, and F760 at leaf scale (F760leaf,fw), which increased. We found that Ts is an important predictor of the light use efficiency of photosynthesis, indicating the importance of Ts in LUE modeling approaches to predict GPP.

Fluorescence Spectroscopic Studies on the Interaction Between 2,5‐Diphenyl Oxazole and Triton X‐100 Micelle

AbstractThe interaction between Triton X‐100 (TX‐100) and 2,5‐diphenyl oxazole (2,5‐DPO) has been investigated successfully by fluorescence and UV–vis study. The fluorescence resonance energy transfer (FRET) between donor TX‐100 and acceptor 2,5‐DPO was examined. UV–vis study shows that there is no formation of ground state complex between donor and acceptor pair in solution. The fluorescence emission and energy transfer efficiency has been determined in both premicellar and postmicellar condition. The distances r = 3.23 and 2.79 nm were calculated in premicellar and postmicellar solutions, respectively. The study indicates that energy transfer in postmicellar environment is remarkably higher than that in case of premicellar situation.

Peltier-Driven Temperature Control for Fluorescent Sensing Platform

Fluorescence dyes are widely used in biomolecule detection/quantification, flow tracing reference for gases and liquids, pathogen detection, and other life science applications. However, fluorescence emission efficiency of the dyes is easily affected by several parameters, such as polarity, pH, and temperature. Therefore, it is essential to monitor and control these parameters for reliable and accurate measurements. We propose a 3D-printed copper cuvette holder (i.materialise, Belgium) joined with a Peltier-based temperature controller platform for stable reading of fluorescence emission from the dye. For demonstration of temperature effects on fluorescence efficiency, rhodamine B, which is one of the widely used fluorescence standards and probes in bioscience, was used. For excitation, 530 nm wavelength lighting was utilized for stimulating the rhodamine B. A Peltier device was controlled with different levels of direct current (DC) to demonstrate the temperature controlling capability of the device and fluorescence efficiency of the rhodamine B was tested with a varying temperature level: 20 ºC to 80 ºC. For our device, the temperature will be monitored by temperature ICs that are attached at three different points of the copper body for uniform temperature heating of the solution in a cuvette. We have monitored the temperature distribution of the copper holder with an external temperature monitor, the DT304, and determined that the temperature is maintained to with a 5 ºC. We plan to monitor the solution temperature directly with the use of an infrared temperature sensor positioned down at the opening of the cuvette. The ambient temperature and the temperature of the opposite junction of the Peltier device will be monitored through the use of two thermocouples. An analysis of several different temperature components of the device allow for a better interpretation of what is happening in the system. Moreover, the implementation of a water-cooling apparatus will allow for a way to quickly decrease the temperature of the cuvette when desirable. These features allow for the sample to be monitored efficiently, allowing for proper stabilization techniques and the ability to fluctuate the temperature when required of an application. In summary, we have developed an 3D-printed copper cuvette holder with a Peltier-based temperature controller platform for stable reading of fluorescence emission from the dye or fluorophore solution. Our compact temperature controller system provides viable option for any fluorometers to easily apply it for temperature stabilization during the fluorescence dye testing. Figure 1

Development of External Stimuli-responsive Organic π Molecules and the Creation of Novel Photo-functions

We have found that the spiro form of aminobenzopyranoxanthene (ABPX) exhibits dual solvatochromic and nanoaggregate fluorescence in organic solvents by spectrophotometric and theoretical analyses. The dual fluorescence properties of ABPX were adjustable in response to water content, and served as a new detection principal for naked-eye visualization (above 0.5 wt%) and quantification (0.010-0.125 wt%) of water in tetrahydrofuran. In investigating the optical properties of a dicationic form of ABPX, ABPX containing linear n-alkyl chains at amino groups were then synthesized. These ABPX exhibited fluorescence emission in the far-red and NIR wavelength regions, and we noted an increased fluorescence quantum efficiency with increasing n-alkyl chain length. To further improve the fluorescence quantum yields, we have designed and synthesized ABPX with different nitrogen-containing fused rings. It was kinetically demonstrated that the structurally rigid conjugation of the xanthene moiety is an effective molecular design for the drastic enhancement of fluorescence emission efficiency.

A Phthalocyanine‐Based Glutathione‐Activated Photosensitizer with a Ferrocenyl Boron Dipyrromethene Dark Quencher for Photodynamic Therapy

AbstractAn efficient near‐infrared‐absorbing dark quencher based on ferrocenyl boron dipyrromethene (BODIPY) has been developed and used to construct a fluorescence resonance energy transfer (FRET)‐based activatable photosensitizer. This smart photosensitizer contains a zinc(II) phthalocyanine as the photosensitizing unit which is conjugated to this dark quencher through a glutathione‐cleavable disulfide linker. The photoactivities of the phthalocyanine unit are largely quenched through FRET to the BODIPY unit followed by photoinduced electron transfer from the attached ferrocenyl moiety. Upon exposure to glutathione in phosphate buffered saline and inside HT29 human colorectal adenocarcinoma cells, the fluorescence emission and singlet oxygen generation efficiency of the photosensitizer are significantly enhanced due to cleavage of the disulfide bond and detachment of the dark quencher from the photosensitizing unit. The activation in fluorescence emission has also been demonstrated in tumor‐bearing nude mice. The glutathione‐responsive behavior has been verified by comparison with the negative results of a non‐cleavable analogue. The results suggest that ferrocenyl BODIPYs could serve as tailorable dark quenchers and the disulfide‐linked phthalocyanine–quencher conjugate acts as an efficient glutathione‐activated photosensitizer for photodynamic therapy.

Multiligand Europium Complexes Incorporated Polyvinylpyrrolidone for Enhanced Solar Cell

Intense reddish-orange fluorescence of Eu3+ is observed in multiligand europium complexes Eu(BA)(TTA)2 and Eu(BA)(TTA)2Phen doped polyvinylpyrrolidone (PVP). Under 367 nm UVA-LED pumping with 708.5 μW, the net emission powers are as high as 204.8 and 243.2 μW, and the total emission photon numbers are derived to be 635.9 × 1012 and 754.9 × 1012 cps for Eu(BA)(TTA)2 and Eu(BA)(TTA)2Phen doped PVP thin films, respectively. It is incredible that the quantum yield (QY) is up to 57.87% in the former; furthermore, as the introduction of Phen, the QY of Eu3+ is increased to 62.03%, verifying the effectiveness of multiligands in photon conversion. Conclusive photon quantification and efficient fluorescence emission reveal the potential of europium complexes/PVP as UV-visible conversion layers for enhanced solar cells.

An approximate procedure for profiling dye molecules with potentials as sensitizers in solar cell application: A DFT/TD-DFT approach

Abstract A DFT/TD-DFT method was employed to study the photovoltaic properties of some metal-free and metal-containing organic compounds (A–G) for dye sensitized solar cells (DSSCs) application. Fluorescence emission ( ϕ f ) and charge collection ( η c ) efficiencies were obtained by deductive logic, and were used to determine the dyes’ incident photon conversion efficiency (IPCE). These parameters were used to evaluate the dye’s suitability for photovoltaic technology. The new approach could be a simple method of predicting dyes’ photovoltaic activities while avoiding the laborious experimental trial and error procedures, although it cannot be used to predict the actual efficiency of a DSSC.

Multifunctional Oligonucleotide-Functionalized Conjugated Oligomer Nanoparticles for Targeted Cancer Cell Imaging and Therapy.

A novel and multifunctional oligonucleotide-functionalized conjugated oligomer nanoparticle (CON) is developed for effective cancer cell imaging and therapy by integration of fluorescence imaging, target recognition, photodynamic therapy (PDT), and chemotherapy. The CON itself possesses the high fluorescence emission efficiency for imaging and can generate reactive oxygen species for PDT. Due to its excellent biocompatibility, easy functional modification, and efficient drug loading and release ability, oligonucleotides enable the CON to be functionalized in many forms. For the target recognition, the CONs are functionalized with oligonucleotides labeled with folate molecules, which can specifically bind the CONs to the tumor cells overexpressing folate receptors. Moreover, the designed oligonucleotide on the CON hybridizes with its complementary sequence to form double-stranded DNA, which enables a sequence-specific loading with doxorubicin for chemotherapy. For different situations, the therapy of chemotherapy and PDT can be used solely or combinatorially. Therefore, this study provides a facile strategy for the multifunctional modification of CONs with oligonucleotides and opens a new avenue for targeted cell imaging and tumor treatment.

Near-infrared photodetection based on erbium chloride borate nanobelts

Erbium compound materials have attracted enormous attentions due to their superior optical properties. Under near-infrared laser illumination at 1530 or 976 nm, these nanobelts exhibit efficient up-conversion fluorescence emission in visible region. A hybrid photodetector based on the synthesized erbium chloride borate nanobelts and a cadmium sulfide nanoribbon. The nice photoresponse of the photodetecor in the near-infrared region, especially in the communication band, is contributed by the effective radiative energy transfer from the erbium ions to the CdS semiconductor. This work provides a feasible basis for the application of rare earth compound nanostructure to high performance near-infrared photodetection devices.

A H₂O₂-Responsive Boron Dipyrromethene-Based Photosensitizer for Imaging-Guided Photodynamic Therapy.

In this study, we demonstrate a novel H2O2 activatable photosensitizer (compound 7) which contains a diiodo distyryl boron dipyrromethene (BODIPY) core and an arylboronate group that quenches the excited state of the BODIPY dye by photoinduced electron transfer (PET). The BODIPY-based photosensitizer is highly soluble and remains nonaggregated in dimethyl sulfoxide (DMSO) as shown by the intense and sharp Q-band absorption (707 nm). As expected, compound 7 exhibits negligible fluorescence emission and singlet oxygen generation efficiency. However, upon interaction with H2O2, both the fluorescence emission and singlet oxygen production of the photosensitizer can be restored in phosphate buffered saline (PBS) solution and PBS buffer solution containing 20% DMSO as a result of the cleavage of the arylboronate group. Due to the higher concentration of H2O2 in cancer cells, compound 7 even with low concentration is particularly sensitive to human cervical carcinoma (HeLa) cells (IC50 = 0.95 μM) but hardly damage human embryonic lung fibroblast (HELF) cells. The results above suggest that this novel BODIPY derivative is a promising candidate for fluorescence imaging-guided photodynamic cancer therapy.

Tailoring the Molecular Skeleton of Aza‐BODIPYs to Design Photostable Red‐Light‐Emitting Laser Dyes

AbstractIn this article the design and characterization of a set of novel red‐light‐emitting laser aza‐BODIPY dyes is reported. The applied synthetic method allows an exhaustive and versatile functionalization of both the dipyrrin core and the boron bridge. From the analysis of the photophysical and laser signatures, we determine the suitable modifications of the chromophoric backbone necessary to modulate the emission spectral region, efficiency and photostability under a strong irradiation regime. These dyes are endowed with efficient fluorescence and laser emission, and are particularly outstanding in terms of their high photostability, a key parameter to guarantee long‐lasting emission in any (bio)technological application. The herein‐reported results support, for the first time, the viability of aza‐BODIPYs as tunable red laser dyes. In fact, the laser performances of some of the tested aza‐BODIPYs surpass those of commercially available laser dyes in the same spectral region.

Promising Fast Energy Transfer System Between Graphene Quantum Dots and the Application in Fluorescent Bioimaging.

Tunable photoluminescence performance of graphene quantum dots (GQDs) is one of the most important topics for the development of GQDs. In this paper, we report lattice-doped GQDs (boron-doped GQDs (B-GQDs) and phosphorus-doped GQDs (P-GQDs)). Because of the matched band structure, the fast energy transfer between blue-emitted B-GQDs (emission wavelength: 460 nm) and orange-emitted P-GQDs (emission wavelength: 630 nm) can induce an efficient fluorescence emission in P-GQDs once B-GQDs are excited under the optimal excitation wavelength of 460 nm. Moreover, with the effective energy transfer, the quantum yield of P-GQDs increased to 0.48, which is much higher than that of pure P-GQDs. We also demonstrated the potentials of this system for fluorescent bioimaging in vitro.

Water Soluble Fluorescent Graphene Nanodots

AbstractWater soluble fluorescent graphene nanodots (GND) have been successfully prepared through a bottom up approach from brominated pyrene via alkaline hydrothermal condensation. FT‐IR, UV‐Vis, Raman, XRD, AFM, and TEM studies have shown the formation of −OH group rich nanodots having graphene features with an approximate size of 90 nm. Steady state and 3D fluorescence studies have shown efficient fluorescence emission with maximum at 540 nm upon excitation at 450 nm in pH≤7. Plasmid deoxyribonucleic acid (plasmid DNA) and bovine serum albumin (BSA) have shown their interaction with GND, which was studied via fluorescence quenching of GND and BSA, respectively. Selective quenching of the Förster resonance energy transfer (FRET) of BSA‐GND conjugate via ascorbic acid (AA) has been used to construct a calibration curve for AA estimation with a linear range and limit of detection of 34.00–112.00 μmole/L and 31.343 μmole/L, respectively. GND has also shown concentration‐dependent turn offchemosensing towards heavy metals like Pb2+, Cu2+, Hg2+ and Zn2+. In‐vitromulticolor fluorescence imaging has been observed in GND‐labelled HeLa (human cervical cancer) and NIH‐3T3 (mouse embryonic fibroblast) cell lines with better uptake by HeLa cells. GND also has shown very high viability for both the cell lines up to the tested concentration of 300 μg/mL.

Polypeptide-based artificial erythrocytes conjugated with near infrared photosensitizers for imaging-guided photodynamic therapy

Photodynamic therapy (PDT) combining with near infrared (NIR) imaging is attractive. However, the intrinsic hypoxia in tumor and consumption of oxygen during treatment will decrease PDT. Here an artificial red cell was prepared using polypeptides conjugated hemoglobin as an oxygen carrier. A NIR photosensitizer-brominated 4,4-difluoro-4-bora-3a,a-diaza-s-indacene (BODIPY-Br2) possessing both high fluorescence emission and singlet oxygen generation efficiency was synthesized and also conjugated to polypeptides to achieve NIR imaging-guided PDT. In vitro studies performed on HepG2 cancer cells verified the oxygen carrier, cancer tracing and curing abilities of the as-prepared polymeric nanoparticles. Even under hypoxia condition, it also obviously increases the cell killing rate when exposed light at a low energy (25 mW/cm2, 10 min). Meanwhile, the fluorescence of BODIPY in NPs would light up cells for real-time imaging. These results show the potential of the biocompatible and biodegradable P-Hb-B NPs for enhancement of simultaneous tracing and treating of cancer.

Variability of sun-induced chlorophyll fluorescence according to stand age-related processes in a managed loblolly pine forest.

Leaf fluorescence can be used to track plant development and stress, and is considered the most direct measurement of photosynthetic activity available from remote sensing techniques. Red and far-red sun-induced chlorophyll fluorescence (SIF) maps were generated from high spatial resolution images collected with the HyPlant airborne spectrometer over even-aged loblolly pine plantations in North Carolina (United States). Canopy fluorescence yield (i.e., the fluorescence flux normalized by the light absorbed) in the red and far-red peaks was computed. This quantifies the fluorescence emission efficiencies that are more directly linked to canopy function compared to SIF radiances. Fluorescence fluxes and yields were investigated in relation to tree age to infer new insights on the potential of those measurements in better describing ecosystem processes. The results showed that red fluorescence yield varies with stand age. Young stands exhibited a nearly twofold higher red fluorescence yield than mature forest plantations, while the far-red fluorescence yield remained constant. We interpreted this finding in a context of photosynthetic stomatal limitation in aging loblolly pine stands. Current and future satellite missions provide global datasets of SIF at coarse spatial resolution, resulting in intrapixel mixture effects, which could be a confounding factor for fluorescence signal interpretation. To mitigate this effect, we propose a surrogate of the fluorescence yield, namely the Canopy Cover Fluorescence Index (CCFI) that accounts for the spatial variability in canopy structure by exploiting the vegetation fractional cover. It was found that spatial aggregation tended to mask the effective relationships, while the CCFI was still able to maintain this link. This study is a first attempt in interpreting the fluorescence variability in aging forest stands and it may open new perspectives in understanding long-term forest dynamics in response to future climatic conditions from remote sensing of SIF.

Enhanced Photoluminescence of Mesostructured Organosilica Films with a High Density of Fluorescent Chromophores

AbstractSynthesis of mesostructured materials containing a high density of organic chromophores in the frameworks is highly desired for applications in unique optical devices using energy transfer. However, a dense accumulation of fluorescent chromophores in solid form generally causes concentration quenching. In this study, dense embedding of the chromophore 1,6‐diphenylpyrene within the framework of mesostructured organosilica films results in efficient blue fluorescence emission with high quantum yields of over 0.75. In contrast to conventional fluorescent films where chromophores are diluted and isolated to suppress concentration quenching, increasing the density of 1,6‐diphenylpyrene moieties within the mesostructured framework leads to the efficient formation of highly emissive excimers. Mesostructured frameworks achieving both high light‐absorptivity and efficient fluorescence emission have great potential in light‐emitting materials, fluorescence sensors, and light‐harvesting components for photoluminescent and photocatalytic systems.

Fluorescence enhancement of a bleach-resistant solution for use in microfluidic devices

Photo-degradation of organic dyes occasionally causes problems in microoptical devices, e.g., microfluidic or droplet lasers, since a strong optical power is concentrated in a small volume for the enhancement of the operation efficiency. Although lanthanide ions provide bleach-resistant fluorescence emitters, their absorption and emission efficiencies are so poor that they usually require a long optical path. Polyethylene glycol is a useful solvent that enhances both the absorption and emission efficiencies due to its turbid characteristic and its ligand effect. A polyethylene glycol solution of europium ions exhibited an 80-fold stronger fluorescence (613 nm wavelength) than an aqueous solution. In addition, solidification induced twofold enhancement of the fluorescence intensity due to the pump light (396 nm wavelength) confinement in a small volume.

Real-Time Intrinsic Fluorescence Visualization and Sizing of Proteins and Protein Complexes in Microfluidic Devices.

Optical detection has become a convenient and scalable approach to read out information from microfluidic systems. For the study of many key biomolecules, however, including peptides and proteins, which have low fluorescence emission efficiencies at visible wavelengths, this approach typically requires labeling of the species of interest with extrinsic fluorophores to enhance the optical signal obtained - a process which can be time-consuming, requires purification steps, and has the propensity to perturb the behavior of the systems under study due to interactions between the labels and the analyte molecules. As such, the exploitation of the intrinsic fluorescence of protein molecules in the UV range of the electromagnetic spectrum is an attractive path to allow the study of unlabeled proteins. However, direct visualization using 280 nm excitation in microfluidic devices has to date commonly required the use of coherent sources with frequency multipliers and devices fabricated out of materials that are incompatible with soft lithography techniques. Here, we have developed a simple, robust, and cost-effective 280 nm LED platform that allows real-time visualization of intrinsic fluorescence from both unlabeled proteins and protein complexes in polydimethylsiloxane microfluidic channels fabricated through soft lithography. Using this platform, we demonstrate intrinsic fluorescence visualization of proteins at nanomolar concentrations on chip and combine visualization with micron-scale diffusional sizing to measure the hydrodynamic radii of individual proteins and protein complexes under their native conditions in solution in a label-free manner.

Synthesis and photoluminescence properties of novel Schiff base type polymer-rare earth complexes containing furfural-based bidentate Schiff base ligands

Luminescent polymer-rare earth complexes are an important class of photoluminescence and electroluminescence materials. Via molecular design, two furfural-based bidentate Schiff base ligands, furfural-aniline (FA) type ligand and furfural-cyclohexylamine (FC) type ligand, were bonded on the side chains of polysulfone (PSF), respectively, forming two functionalized macromolecules, PSF-FA and PSF-FC. And then through respective coordination reactions of the two functionalized macromolecules with Eu(Ⅲ) ion and Tb(Ⅲ) ion, novel luminescent binary and ternary (with 1,10-phenanthroline as the second ligand) polymer-rare earth complexes were synthesized. For these complexes, on basis of the characterization of their chemical structures, they photoluminescence properties were main researched, and the relationship between their luminescent properties and structures was explored. The experimental results show that the complexes coming from PSF-FA and Eu(Ⅲ) ion including binary and ternary complexes emit strong red luminescence, indicating that the bonded bidentate Schiff base ligand FA can sensitize the fluorescence emission of Eu(III) ion. While the complexes coming from PSF-FC and Tb(Ⅲ) ion produce green luminescence, displaying that the bonded bidentate Schiff base ligand FC can sensitize the fluorescence emission of Tb(Ⅲ) ion. The fluorescence emission intensities of the ternary complexes were stronger than that of binary complexes, reflecting the important effect of the second ligand. The fluorescence emission of the solid film of complexes is much stronger than that of the solutions of complexes. Besides, by comparison, it is found that the furfural (as a heteroaromatic compound)-based Schiff base type polymer-rare earth complexes have stronger fluorescence emission and higher energy transfer efficiency than salicylaldehyde (as a common aromatic compound)-based Schiff base type polymer-rare earth complexes.