Förster Resonance Energy Transfer Research Articles

CdSe/ZnS Quantum Rods (QRs) and Phenyl Boronic Acid BODIPY as Efficient Förster Resonance Energy Transfer (FRET) Donor–Acceptor Pair

The reversibility of the covalent interaction between boronic acids and 1,2- or 1,3-diols has put the spotlight on this reaction for its potential in the development of sensors and for the fishing of bioactive glycoconjugates. In this work, we describe the investigation of this reaction for the reversible functionalization of the surface of CdSe/ZnS Quantum Rods (QRs). With this in mind, we have designed a turn-off Förster resonance energy transfer (FRET) system that ensures monitoring the extent of the reaction between the phenyl boronic residue at the meso position of a BODIPY probe and the solvent-exposed 1,2-diols on QRs’ surface. The reversibility of the corresponding boronate ester under oxidant conditions has also been assessed, thus envisioning the potential sensing ability of this system.

Metal Ion Responsive Luminescent Bio-templated Co-assemblies: Label-Free Detection of Multi-Metal Ions in Aqueous Media.

Recently, anionic bio-templates have emerged as promising platforms for designing dynamic and stimuli-responsive chromophoric assemblies capable of light harvesting in aqueous media thereby mimicking natural photosynthesis. Here, we present multi-metal ion-responsive luminescent co-assemblies between cationic pyrene-imidazolium amphiphile and anionic bio-templates (ATP, heparin, and DNA) in aqueous media. The anionic bio-templates enhance Förster resonance energy transfer (FRET) in the co-assemblies, with pyrene serving as an excellent donor for generating tunable multi-luminescent materials with embedded acceptor dyes. However, a significant loss in energy transfer towards acceptor dyes was observed in the presence of various metal ions, attributed to excimeric emission quenching facilitated by electron transfer between the pyrene chromophore and metal ions. Interestingly, detailed studies revealed that only ATP-based co-assemblies exhibited quenching phenomena in the presence of metal ions, contrasting with heparin and ctDNA co-assemblies. Additionally, label-free detection of multi-metal ions in aqueous environments, such as Fe2+, Fe3+, and Cu2+ ions, was successfully achieved with lower detection limits of 0.01 μM (3 ppb), 0.12 μM (30 ppb), and 0.58 μM (150 ppb) respectively. These co-assemblies hold significant promise for practical applications in environmental and biomedical sensing, enabling sensitive monitoring of metal ion concentrations.

Pulsed-Interleaved-Excitation Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy.

We report on pulsed-interleaved-excitation two-dimensional fluorescence lifetime correlation spectroscopy (PIE 2D FLCS) to study biomolecular structural dynamics with high sensitivity and high time resolution using Förster resonance energy transfer (FRET). PIE 2D FLCS is an extension of 2D FLCS, which is a unique single-molecule fluorescence method that uses fluorescence lifetime information to distinguish different fluorescence species in equilibrium and resolves their interconversion dynamics with a submicrosecond time resolution. Because 2D FLCS has used only a single-color excitation so far, it was difficult to distinguish a very low-FRET (or zero-FRET) species from only donor-labeled species. We overcome this difficulty by implementing the PIE scheme (i.e., alternate excitation of the donor and acceptor dyes using two temporally interleaved excitations with different colors) to 2D FLCS, realizing two-color excitation and two-color fluorescence detection in 2D FLCS. After proof-of-principle PIE 2D FLCS analysis on the photon data synthesized with Monte Carlo simulation, we apply PIE 2D FLCS to a DNA-hairpin sample and show that this method readily distinguishes four fluorescent species, i.e., high-FRET, low-FRET, and two single-dye-labeled species. In addition, we show that PIE 2D FLCS can also quantitatively evaluate the contributions of the donor-acceptor spectral crosstalk, which often appears as artifacts in FRET studies and degrades the information obtained.

Implementation of FRET Spectrometry Using Temporally Resolved Fluorescence: A Feasibility Study

Förster resonance energy transfer (FRET) spectrometry is a method for determining the quaternary structure of protein oligomers from distributions of FRET efficiencies that are drawn from pixels of fluorescence images of cells expressing the proteins of interest. FRET spectrometry protocols currently rely on obtaining spectrally resolved fluorescence data from intensity-based experiments. Another imaging method, fluorescence lifetime imaging microscopy (FLIM), is a widely used alternative to compute FRET efficiencies for each pixel in an image from the reduction of the fluorescence lifetime of the donors caused by FRET. In FLIM studies of oligomers with different proportions of donors and acceptors, the donor lifetimes may be obtained by fitting the temporally resolved fluorescence decay data with a predetermined number of exponential decay curves. However, this requires knowledge of the number and the relative arrangement of the fluorescent proteins in the sample, which is precisely the goal of FRET spectrometry, thus creating a conundrum that has prevented users of FLIM instruments from performing FRET spectrometry. Here, we describe an attempt to implement FRET spectrometry on temporally resolved fluorescence microscopes by using an integration-based method of computing the FRET efficiency from fluorescence decay curves. This method, which we dubbed time-integrated FRET (or tiFRET), was tested on oligomeric fluorescent protein constructs expressed in the cytoplasm of living cells. The present results show that tiFRET is a promising way of implementing FRET spectrometry and suggest potential instrument adjustments for increasing accuracy and resolution in this kind of study.

DNA tetrahedron-based dual-signal fluorescence detection of apoE4 gene sites on a microplate reader.

As a neurodegenerative disorder, Alzheimer's disease (AD) is characterized by cognitive dysfunction and behavioral impairment. Among the various genetic risk factors for AD, apoE4 gene plays a pivotal role in the onset and progression of AD, and detection of apoE4 gene holds significance for prevention and early diagnosis of AD. Herein, dual-signal fluorescence detection of fragments associated with apoE ε4 allele near codon 112 (Tc1) and codon 158 (Tc2) was achieved using DNA tetrahedron nanostructure (DTN). The Förster resonance energy transfer (FRET) process in the DTN was initiated in which the nucleic acid intercalating dye thiazole orange (TO) served as the donor and the cyanine dyes of cyanine3 (Cy3) and cyanine5 (Cy5) at the two vertices of DTN served as the acceptors. In the presence of Tc1 and Tc2, the FRET process between TO and the cyanine dyes was hindered by the enzymatic cleavage reaction, which ensures the dual-signal fluorescence assay of apoE4 gene sites. The limit of detection for Tc1 and Tc2 was estimated to be 0.82nM and 0.77nM, respectively, and the whole assay was accomplished within 1h on a microplate reader. The proposed method thus possesses the advantages of easy operation, short detection time, and high-throughput capability.

Fluorescent antenna based on Förster resonance energy transfer (FRET) for optical wireless communications

The use of fluorescent antennas in optical wireless communications (OWC) has been demonstrated previously, and it has been shown that it is an efficient method for enhancing receiver performance, providing both signal gain and a wide field of view (FoV). To achieve a high concentration gain at the receiver output, the selected fluorophores should have a high photoluminescence quantum yield (PLQY), limited overlap between their absorption and emission spectra, and emit light that can be efficiently detected. In addition, to support a high modulation bandwidth, the photoluminescence (PL) lifetime of the fluorophore needs to be short. In this paper, we propose a new fluorescent antenna architecture based on Förster resonance energy transfer (FRET). Our results show that, due to the photophysical interactions between the energy donor and energy acceptor, the use of FRET simultaneously increases PLQY and reduces PL lifetime. Additionally, employing FRET leads to an increased Stokes shift, ensuring that the emitted light has longer wavelengths, thus reducing self-absorption. This shift can also increase the efficiency with which the fluorescence is detected by a typical silicon (Si) photodetector. Consequently, our OWC results show that a new FRET-based antenna can achieve a significantly higher concentration gain and a wider transmission bandwidth than a conventional non-FRET antenna, leading to much higher data rates.

LRMP inhibits cAMP potentiation of HCN4 channels by disrupting intramolecular signal transduction

Lymphoid restricted membrane protein (LRMP) is a specific regulator of the hyperpolarization-activated cyclic nucleotide-sensitive isoform 4 (HCN4) channel. LRMP prevents cAMP-dependent potentiation of HCN4, but the interaction domains, mechanisms of action, and basis for isoform-specificity remain unknown. Here, we identify the domains of LRMP essential for this regulation, show that LRMP acts by disrupting the intramolecular signal transduction between cyclic nucleotide binding and gating, and demonstrate that multiple unique regions in HCN4 are required for LRMP isoform-specificity. Using patch clamp electrophysiology and Förster resonance energy transfer (FRET), we identified the initial 227 residues of LRMP and the N-terminus of HCN4 as necessary for LRMP to associate with HCN4. We found that the HCN4 N-terminus and HCN4-specific residues in the C-linker are necessary for regulation of HCN4 by LRMP. Finally, we demonstrated that LRMP-regulation can be conferred to HCN2 by addition of the HCN4 N-terminus along with mutation of five residues in the S5 region and C-linker to the cognate HCN4 residues. Taken together, these results suggest that LRMP inhibits HCN4 through an isoform-specific interaction involving the N-terminals of both proteins that prevents the transduction of cAMP binding into a change in channel gating, most likely via an HCN4-specific orientation of the N-terminus, C-linker, and S4-S5 linker.

High Q Ultra‐Low Threshold Lasing in Conjugated Polymer Blend Microspheres Promoted by FRET

AbstractConjugated polymer (CP) based microspheres of very high definition and outstanding photonic and luminescent properties are prepared by a technique based on slow solvent‐controlled diffusion into micelles formed by the surfactant cetyl(trimethyl)ammonium bromide (CTAB). Poly[(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,8‐diyl)] (F8BT) and mixtures of F8BT with poly[2‐methoxy‐5‐(2’‐ethylhexyloxy)‐1,4‐phenylene vinylene (MEH‐PPV) are used for this purpose. Microspheres with diameters between 1 and 10 µm are obtained and structural characterization by AFM and SEM demonstrate good sphericity and low surface roughness. Correspondingly, spontaneous emission of the spheres exhibits Mie resonances of high quality factor (Q > 1800), appropriately reproduced employing standard Mie theory. Upon pumping the microspheres with a pulsed Nd:YAG laser operating at 355 nm lasing at low threshold fluences (≈ 4 µJ cm−2) is obtained with instrumentally limited linewidths corresponding to Q > 18000. Lasing in microspheres composed of blends of both CPs coupled by Förster resonant energy transfer (FRET), on the other hand, is observed at extremely low threshold fluences down to ≈ 0.5 µJ cm−2. Spherical structures based on appropriate blends of CPs are therefore promising candidates in the search for low‐threshold organic microlasers excited by light‐emitting diodes or diode lasers or for ultrasensitive optical sensing.

USING FÖRSTER RESONANCE ENERGY TRANSFER (FRET) TO UNDERSTAND THE UBIQUITINATION LANDSCAPE.

Förster resonance energy transfer (FRET) is a fluorescence technique that allows quantitative measurement of protein interactions, kinetics and dynamics. This review covers the use of FRET to study the structures and mechanisms of ubiquitination and related proteins. We survey FRET assays that have been developed where donor and acceptor fluorophores are placed on E1, E2 or E3 enzymes and ubiquitin (Ub) to monitorsteady-stateand real-time transfer of Ub through the ubiquitination cascade. Specialized FRET probesplaced onUb andUb-likeproteins have been developed to monitor Ub removal by deubiquitinating enzymes (DUBs)that result in a loss of aFRET signal upon cleavage of the FRET probes. FRET has also been used to understand conformational changes in large complexes such as multimeric E3 ligases and theproteasome,frequently using sophisticated single molecule methods. Overall, FRET is a powerful tool to help unravel the intricacies of the complex ubiquitination system.

FRET Assays for the Identification of C. albicans HSP90-Sba1 and Human HSP90α-p23 Binding Inhibitors.

Heat shock protein 90 (HSP90) is a critical target for anticancer and anti-fungal-infection therapies due to its central role as a molecular chaperone involved in protein folding and activation. In this study, we developed in vitro Förster Resonance Energy Transfer (FRET) assays to characterize the binding of C. albicans HSP90 to its co-chaperone Sba1, as well as that of the homologous human HSP90α to p23. The assay for human HSP90α binding to p23 enables selectivity assessment for compounds aimed to inhibit the binding of C. albicans HSP90 to Sba1 without affecting the physiological activity of human HSP90α. The combination of the two assays is important for antifungal drug development, while the assay for human HSP90α can potentially be used on its own for anticancer drug discovery. Since ATP binding of HSP90 is a prerequisite for HSP90-Sba1/p23 binding, ATP-competitive inhibitors can be identified with the assays. The specificity of binding of fusion protein constructs-HSP90-mNeonGreen (donor) and Sba1-mScarlet-I (acceptor)-to each other in our assay was confirmed via competitive inhibition by both non-labeled Sba1 and known ATP-competitive inhibitors. We utilized the developed assays to characterize the stability of both HSP90-Sba1 and HSP90α-p23 affinity complexes quantitatively. Kd values were determined and assessed for their precision and accuracy using the 95.5% confidence level. For HSP90-Sba1, the precision confidence interval (PCI) was found to be 70-120 (100 ± 20) nM while the accuracy confidence interval (ACI) was 100-130 nM. For HSP90α-p23, PCI was 180-260 (220 ± 40) nM and ACI was 200-270 nM. The developed assays were used to screen a nucleoside-mimetics library of 320 compounds for inhibitory activity against both C. albicans HSP90-Sba1 and human HSP90α-p23 binding. No novel active compounds were identified. Overall, the developed assays exhibited low data variability and robust signal separation, achieving Z factors > 0.5.

Identification of Riluzole Derivatives as Novel Calmodulin Inhibitors with Neuroprotective Activity by a joint synthesis, biosensor, and computational guided strategy

The development of new molecules for the treatment of calmodulin related cardiovascular or neurodegenerative diseases is an interesting goal. In this work, we introduce a novel strategy with four main steps: (1) chemical synthesis of target molecules, (2) Förster Resonance Energy Transfer (FRET) biosensor development and in vitro biological assay of new derivatives, (3) Cheminformatics models development and in vivo activity prediction, and (4) Docking studies. This strategy is illustrated with a case study. Firstly, a series of 4-substituted Riluzole derivatives 1-3 were synthetized through a strategy that involves the construction of the 4-bromoriluzole framework and its further functionalization via palladium catalysis or organolithium chemistry. Next, a FRET biosensor for monitoring Ca2+-dependent CaM-ligands interactions has been developed and used for the in vitro assay of Riluzole derivatives. In particular, the best inhibition (80%) was observed for 4-methoxyphenylriluzole 2b. Besides, we trained and validated a new Networks Invariant, Information Fusion, Perturbation Theory, and Machine Learning (NIFPTML) model for predicting probability profiles of in vivo biological activity parameters in different regions of the brain. Next, we used this model to predict the in vivo activity of the compounds experimentally studied in vitro. Last, docking study conducted on Riluzole and its derivatives has provided valuable insights into their binding conformations with the target protein, involving calmodulin and the SK4 channel. This new combined strategy may be useful to reduce assay costs (animals, materials, time, and human resources) in the drug discovery process of calmodulin inhibitors.

Transfer of ANS-Like Drugs from Micellar Drug Delivery Systems to Albumin Is Highly Favorable and Protected from Competition with Surfactant by "Reserved" Binding Sites.

Micellar drug delivery systems (MDDS) for the intravenous administration of poorly soluble drugs have great advantages over alternative formulations in terms of the safety of their excipients, storage stability, and straightforward production. A classic example is mixed micelles of glycocholate (GC) and lecithin, both endogenous substances in human blood. What limits the use of MDDS is the complexity of the transitions after injection. In particular, as the MDDS disintegrate partially or completely after injection, the drug has to be transferred safely to endogenous carriers in the blood, such as human serum albumin (HSA). If this transfer is compromised, the drug might precipitate─a process that needs to be excluded under all circumstances. The key question of this paper is whether the high local concentration of GC at the moment and site of MDDS dissolution might transiently saturate HSA binding sites and, hence, endanger quick drug transfer. To address this question, we have used a new approach, which is time-resolved fluorescence spectroscopy of the single tryptophan in HSA, Trp-214, to characterize the competitive binding of GC and the drug substitute anilinonaphthalenesulfonate (ANS) to HSA. Time-resolved fluorescence of Trp-214 showed important advantages over established methods for tackling this problem. ANS has been the standard "model drug" to study albumin binding for decades, given its structural similarity to the class of naphthalene-containing acidic drugs and the fact that it is displaced from HSA by numerous drugs (which presumably bind to the same sites). Our complex global fit uses the critical approximation that the average lifetimes behave similarly to a single lifetime, but the resulting errors are found to be moderate and the results provide a convincing explanation of the, at first glance, counterintuitive behavior. Accordingly, and largely in line with the literature, we observed two types of sites binding ANS at HSA: 3 type A, rather peripheral, and 2 type B, likely more central sites. The latter quench Trp-214 by Förster Resonance Energy Transfer (FRET) with a rate constant of ≈0.4 ns-1 per ANS. Adding millimolar concentrations of GC displaces ANS from the A sites but not from B sites. At incomplete ANS saturation, this causes a GC-induced translocation of ANS from A to the more FRET-active B sites. This leads to the apparent paradox that the partial displacement of ANS from HSA increases its quenching effect on Trp-214. The most important conclusion is that (ANS-like) drugs cannot be displaced from the type-B sites, and consequently, drug transfer to these sites is not impaired by competitive binding of GC in the vicinity of a dissolving micelle. The second conclusion is that for unbound GC above the CMC (9 mM), ANS equilibrates between HSA and GC micelles but with a strong preference for free sites on HSA. That means that even persisting micelles would lose their cargo readily once exposed to HSA. For all MDDS sharing this property, targeted drug delivery approaches involving them as the nanocarrier would be pointless.

AptaShield: A Universal Signal-Transduction System for Fast and High-Throughput Optical Molecular Biosensing.

Biosensing technologies are often described to provide facile, sensitive, and minimally to noninvasive detection of molecular analytes across diverse scientific, environmental, and clinical diagnostic disciplines. However, commercialization has been very limited mostly due to the difficulty of biosensor reconfiguration for different analyte(s) and limited high-throughput capabilities. The immobilization of different biomolecular probes (e.g., antibodies, peptides, and aptamers) requires the sensor surface chemistry to be tailored to provide optimal probe coupling, orientation, and passivation and prevent nonspecific interactions. To overcome these challenges, here we report the development of a solution-phase biosensor consisting of an engineered aptamer, the AptaShield, capable of universally binding to any antigen recognition site (Fab') of fluorescently labeled immunoglobulins (IgG) produced in rabbits. The resulting AptaShield biosensor relies on a low affinity dynamic equilibrium between the fluorescently tagged aptamer and IgG to generate a specific Förster resonance energy transfer (FRET) signal. As the analyte binds to the IgG, the AptaShield DNA aptamer-IgG complex dissociates, leading to an analyte concentration-dependent decrease of the FRET signal. The biosensor demonstrates high selectivity, specificity, and reproducibility for analyte quantification in different biological fluids (e.g., urine and blood serum) in a one-step and low sample volume (0.5-6.25 μL) format. The AptaShield provides a universal signal transduction mechanism as it can be coupled to different rabbit antibodies without the need for aptamer modification, therefore representing a robust high-throughput solution-phase technology suitable for point-of-care applications, overcoming the current limitations of gold standard enzyme-linked immunosorbent assays (ELISA) for molecular profiling.

Boosting Excited-State Energy Transfer by Anchoring Dipole Orientation in Binary Thermally Activated Delayed Fluorescence/J-Aggregate Assemblies.

Förster resonance energy transfer (FRET) has been widely applied in fluorescence imaging, sensing and so on, while developing useful strategy of boosting FRET efficiency becomes a key issue that limits the application. Except optimizing spectral properties, promoting orientation factor (κ2) has been well discussed but rarely utilized for boosting FRET. Herein, we constructed binary nano-assembling of two thermally activated delayed fluorescence (TADF) emitters (2CzPN and DMAC-DPS) with J-type aggregate of cyanine dye (C8S4) as doping films by taking advantage of their electrostatic interactions. Time-resolved spectroscopic measurements indicated that 2CzPN/Cy-J films exhibit an order of magnitude higher kFRET than DMAC-DPS/Cy-J films. Further quantitative analysing on kFRET and kDET indicated higher orientation factor (κ2) in 2CzPN/Cy-J films play a key role for achieving fast kFRET, which was subsequently confirmed by anisotropic measurements. Corresponding DFT/TDDFT calculation revealed strong "two-point" electrostatic anchoring in 2CzPN/Cy-J films that is responsible for highly orientated transitions. We provide a new strategy for boosting FRET in nano-assemblies, which might be inspired for designing FRET-based devices of sensing, imaging and information encryption.

Next‐Generation Metabolic Glycosylation Reporters Enable Detection of Protein O−GlcNAcylation in Living Cells without S‐Glyco Modification

AbstractProtein O−GlcNAcylation is a ubiquitous posttranslational modification of cytosolic and nuclear proteins involved in numerous fundamental regulation processes. Investigation of O−GlcNAcylation by metabolic glycoengineering (MGE) has been carried out for two decades with peracetylated N‐acetylglucosamine (GlcNAc) and N‐acetylgalactosamine derivatives modified with varying reporter groups. Recently, it has been shown that these derivatives can result in non‐specific protein labeling termed S‐glyco modification. Here, we report norbornene‐modified GlcNAc derivatives with a protected phosphate at the anomeric position and their application in MGE. These derivatives overcome two limitations of previously used O−GlcNAc reporters. They do not lead to detectable S‐glyco modification, and they efficiently react in the inverse‐electron‐demand Diels–Alder (IEDDA) reaction, which can be carried out even within living cells. Using a derivative with an S‐acetyl‐2‐thioethyl‐protected phosphate, we demonstrate the protein‐specific detection of O−GlcNAcylation of several proteins and the protein‐specific imaging of O−GlcNAcylation inside living cells by Förster resonance energy transfer (FRET) visualized by confocal fluorescence lifetime imaging microscopy (FLIM).

A molecular dynamics simulation study of glycine/serine octapeptides labeled with 2,3-diazabicyclo[2.2.2]oct-2-ene fluorophore.

The compound 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) is a versatile fluorophore widely used in Förster resonance energy transfer (FRET) spectroscopy studies due to its remarkable sensitivity, enabling precise donor-acceptor distance measurements, even for short peptides. Integrating time-resolved and FRET spectroscopies with molecular dynamics simulations provides a robust approach to unravel the structure and dynamics of biopolymers in a solution. This study investigates the structural behavior of three octapeptide variants: Trp-(Gly-Ser)3-Dbo, Trp-(GlyGly)3-Dbo, and Trp-(SerSer)3-Dbo, where Dbo represents the DBO-containing modified aspartic acid, using molecular dynamics simulations. Glycine- and serine-rich amino acid fragments, common in flexible protein regions, play essential roles in functional properties. Results show excellent agreement between end-to-end distances, orientational factors from simulations, and the available experimental and theoretical data, validating the reliability of the GROMOS force field model. The end-to-end distribution, modeled using three Gaussian distributions, reveals a complex shape, confirmed by cluster analysis highlighting a limited number of significant conformations dominating the peptide landscape. All peptides predominantly adopt a disordered state in the solvent, yet exhibit a compact shape, aligning with the model of disordered polypeptide chains in poor solvents. Conformations show marginal dependence on chain composition, with Ser-only chains exhibiting slightly more elongation. This study enhances our understanding of peptide behavior, providing valuable insights into their structural dynamics in solution.

Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications.

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

Water‐Soluble Fluorescent Polymer Dyes with Tunable Emission Spectra for Flow Cytometry Applications

AbstractThe application of spectrally unique, bright, and water‐soluble fluorescent dyes is indispensable for the analysis of biological systems. Multiparameter flow cytometry is a powerful tool for characterization of mixed cell populations. To discriminate the different cell populations, they are typically stained by a set of fluorescent reagents, e.g., antibody‐fluorophore conjugates. The number of parameters which can be studied simultaneously strongly depends on the availability of reagents which can be differentiated by their spectral properties. In this study a series of fluorescent polymer dyes was developed, that can be excited with a single violet laser (405 nm) but distinguished by their unique emission spectra. The polyfluorene‐based polymers can be used on their own, or in combination with covalently bound small‐molecule dyes to generate energy transfer constructs to red‐shift the emission wavelength based on Förster resonance energy transfer (FRET). The polymer dyes were utilized in a biological flow cytometry assay by conjugating several of them to antibodies, demonstrating their effectiveness as reagents. This report represents the first systematic investigation of structure–property relationships for this type of fluorescent dyes.

Water-Soluble Fluorescent Polymer Dyes with Tunable Emission Spectra for Flow Cytometry Applications.

The application of spectrally unique, bright, and water-soluble fluorescent dyes is indispensable for the analysis of biological systems. Multiparameter flow cytometry is a powerful tool for characterization of mixed cell populations. To discriminate the different cell populations, they are typically stained by a set of fluorescent reagents, e.g., antibody-fluorophore conjugates. The number of parameters which can be studied simultaneously strongly depends on the availability of reagents which can be differentiated by their spectral properties. In this study a series of fluorescent polymer dyes was developed, that can be excited with a single violet laser (405 nm) but distinguished by their unique emission spectra. The polyfluorene-based polymers can be used on their own, or in combination with covalently bound small-molecule dyes to generate energy transfer constructs to red-shift the emission wavelength based on Förster resonance energy transfer (FRET). The polymer dyes were utilized in a biological flow cytometry assay by conjugating several of them to antibodies, demonstrating their effectiveness as reagents. This report represents the first systematic investigation of structure-property relationships for this type of fluorescent dyes.

Temperature- and pH-modulated Förster resonance energy transfer for establishment of white light emission

Heteroatom doping is an efficient approach for increasing fluorescence efficiency of carbon dots (CDs). Co-doping with heteroatoms may add additional active sites to CDs and expand their different capabilities. A simple and low-cost hydrothermal method was used to prepare nitrogen- and also nitrogen- and sulfur-rich CDs-decorated graphene oxide, NCDs-GO and N,SCDs-GO, respectively. The as-prepared hybrid CDs-GO samples are responsive to pH and temperature variations, implying pH and temperature-dependent fluorescence properties. The different properties of the CDs-GO hybrids were investigated using transmission electron microscopy and also energy-dispersive X-ray, Raman, and Fourier transform infrared spectroscopies. The ternary mixture of N,SCDs-GO, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), and rhodamine B (RB) was also used to detect pH changes via the Förster resonance energy transfer (FRET) process, where N,SCDs-GO and RB play the role of donor and acceptor, respectively, in the PDMAEMA aqueous solution medium. Fluorescence and ultraviolet–visible spectroscopies were used to assess the feasibility and efficiency of the FRET process. The donor–acceptor ratio was changed to get the broadly adjustable photoluminescence emission from blue to red, and especially white light. The aqueous ternary mixture has a wide range of potential applications in pH sensing, temperature monitoring, and anticounterfeiting. This colloidal system with controllable fluorescence and white light emission was used to design anticounterfeiting inks for security-marking of wood samples.