Energy Transfer Acceptor Research Articles

Theoretical model of donor–donor and donor–acceptor energy transfer on a nanosphere

In this study, we introduce a novel advancement in the field of theoretical exploration. Specifically, we investigate the transfer and trapping of electronic excitations within a two-component disordered system confined to a finite volume. The implications of our research extend to energy transfer phenomena on spherical nanoparticles, characterized by randomly distributed donors and acceptors on their surface. Utilizing the three-body Padé approximant technique, previously employed in single-component systems, we apply it to address the challenge of trapping within our system. To validate the robustness of our model, we conduct Monte Carlo simulations on a donor–acceptor system positioned on a spherical nanoparticle. In particular, very good agreement between the model and Monte Carlo simulations has been found for donor fluorescence intensity decay.

Self-Reporting Conjugated Polymer Nanoparticles for Superoxide Generation and Detection.

Conjugated polymer nanoparticles (CPNs or Pdots) have become increasingly popular fluorophores for multimodal applications that combine imaging with phototherapeutic effects. Reports of CPNs in photodynamic therapy applications typically focus on their ability to generate singlet oxygen. Alternatively, CPN excited states can interact with oxygen to form superoxide radical anion and a CPN-based hole polaron, both of which can have deleterious effects on fluorescence properties. Here, we demonstrate that CPNs prepared from the common conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT, also known as F8BT) generate superoxide upon irradiation. We use the same CPNs to detect superoxide by doping them with a superoxide-responsive hydrocyanine dye developed by Murthy and co-workers. Superoxide induces off-to-on fluorescence switching by converting quenching hydrocyanine dyes to fluorescent cyanine dyes that act as fluorescence resonance energy transfer (FRET) acceptors for PFBT chromophores. Amplified FRET from the multichromophoric CPNs yields fluorescence signal intensities that are nearly 50 times greater than when the dye is excited directly or over 100 times greater when signal readout is from the CPN channel. The dye loading level governs the maximum amount of superoxide that induces a change in fluorescence properties and also influences the rate of superoxide generation by furnishing competitive excited state deactivation pathways. These results suggest that CPNs can be used to deliver superoxide in applications in which it is desirable and provide a caution for fluorescence-based CPN applications in which superoxide can damage fluorophores.

Multidimension‐Regulated Dynamic Timing Control Over Multicolor Emission of Host–Guest Assemblies for Information Encryption and Advanced Anti‐Counterfeiting

AbstractDynamical control over molecular luminescence, especially in a time‐dependent manner, holds great promise for the development of smart luminescent materials for anti‐counterfeiting and preventing information leakage. Herein, a series of self‐assembled systems are reported using pillar[5]arene (DMP[5]) and spiropyran derivatives (SP‐C4‐Py). The assemblies rely on the time‐encoded locking and unlocking ring‐switching and fluorescence resonance energy transfer (FRET) units for information camouflage and multilevel encryption. DMP[5] with cyan solid fluorescence color acts as the host and energy transfer (EnT) donor, while photochromic SP‐C4‐Py with the ring‐opened and closed isomers acts as guest and EnT acceptor. When irradiated, the assemblies undergo a time‐dependent luminescence color change ranging from cyan to yellow to red through a FRET process. The molar ratio of host and guest in the assembly systems affects the FRET efficiency, and the power of the irradiation source influences the isomerization degree and rate of SP‐C4‐Py, allowing for precise control over the fluorescent color transition time. The combination of molecular composition and external stimuli governs the kinetics of color change, resulting in a difference in the appearance time of a specific fluorescent color pre‐designed as correct authorized information. By combining these diverse assembles in one label, information encryption and dynamic information identification are achieved in the dimensions of time, ratio, and light power. This time‐dependent feature offers the assembly materials with a multilevel security and provides new possibilities for anti‐counterfeiting and blocking information leakage.

Construction of an autofluorescence interference-free phosphorescence biosensor for the specific detection of TK1 mRNA

The anti-interference ability of biosensors is critical for detection in biological samples. Fluorescence-based sensors are subject to interference from self-luminescent substances in biological matrices. Therefore, phosphorescent sensors stand out among biosensors due to their lack of self-luminescence background. In this study, a phosphorescent sensor was constructed, which can accurately detect thymidine kinase 1 (TK1) mRNA in biological samples and avoid autofluorescence interference. When there is no target, polydopamine (PDA) is used as the phosphorescence resonance energy transfer (PRET) acceptor to quench the phosphorescence of the persistently luminescent (PL) nanomaterial. When there is a target, the DNA modified by the PL nanomaterial is replaced by the hairpin H and removed away from the PDA, resulting in a rebound in phosphorescence. The phosphorescent sensor exhibits a good linear relationship in the TK1 mRNA concentration range of 0–200 nM, and the detection limit was 1.74 nM. The sensor fabricated in this study can effectively avoid interference from spontaneous fluorescence in complex biological samples, and sensitively and precisely detect TK1 mRNA in serum samples, providing a powerful tool to more accurately detect biomarkers in biological samples.

Dual suppression amplification based on resonance energy transfer and enzymatic biocatalytic precipitation for IgG electrochemiluminescence ultrasensitive assay

Due to the necessity of ultrasensitive bioassays in life science, electrochemiluminescence (ECL) methodologies coupled with amplification strategies has drawn great attention recently. Herein, a versatile and robust dual suppression-based signal amplification strategy was proposed for IgG specifically ultrasensitive detection. A sandwich ECL sensor was constructed by employing Ru(bpy)32+ adsorbed on silica microspheres (Ru@SiO2) as luminophor. Fe3O4 nanoparticles (Fe3O4 NPs) were introduced on sensing platform through an antigen-antibody affinity, which played double roles. As an acceptor of resonance energy transfer (RET), Fe3O4 NPs remarkably quenched the ECL signal of Ru@SiO2. Meanwhile, Fe3O4 NPs, as a typical peroxidase-mimicking enzyme, catalyzed H2O2 to produce insoluble product based on enzymatic biocatalytic precipitation (BCP). As such, an efficient dual suppressive ECL platform has been achieved by the integration of ECL-RET and BCP techniques, which has been applied to ultrasensitively detect IgG with a linear range and limit of detection of 10 fg/mL to 1 μg/mL and 4.9 fg/mL, respectively. The new integrated system with RET and BCP may provide a potential promising in the development of highly efficient ECL systems for clinical diagnosis.

MScarlet3: a brilliant and fast-maturing red fluorescent protein.

We report the evolution of mScarlet3, a cysteine-free monomeric red fluorescent protein with fast and complete maturation, as well as record brightness, quantum yield (75%) and fluorescence lifetime (4.0 ns). The mScarlet3 crystal structure reveals a barrel rigidified at one of its heads by a large hydrophobic patch of internal residues. mScarlet3 behaves well as a fusion tag, displays no apparent cytotoxicity and it surpasses existing red fluorescent proteins as a Förster resonance energy transfer acceptor and as a reporter in transient expression systems.

Structural and optical variation of pseudoisocyanine aggregates nucleated on DNA substrates

Coherently coupled pseudoisocyanine (PIC) dye aggregates have demonstrated the ability to delocalize electronic excitations and ultimately migrate excitons with much higher efficiency than similar designs where excitations are isolated to individual chromophores. Here, we report initial evidence of a new type of PIC aggregate, formed through heterogeneous nucleation on DNA oligonucleotides, displaying photophysical properties that differ significantly from previously reported aggregates. This new aggregate, which we call the super aggregate (SA) due to the need for elevated dye excess to form it, is clearly differentiated from previously reported aggregates by spectroscopic and biophysical characterization. In emission spectra, the SA exhibits peak narrowing and, in some cases, significant quantum yield variation, indicative of stronger coupling in cyanine dyes. The SA was further characterized with circular dichroism and atomic force microscopy observing unique features depending on the DNA substrate. Then by integrating an AlexaFluorTM 647 (AF) dye as an energy transfer acceptor into the system, we observed mixed energy transfer characteristics using the different DNA. For example, SA formed with a rigid DNA double crossover tile (DX-tile) substrate resulted in AF emission sensitization. While SA formed with more flexible non-DX-tile DNA (i.e. duplex and single strand DNA) resulted in AF emission quenching. These combined characterizations strongly imply that DNA-based PIC aggregate properties can be controlled through simple modifications to the DNA substrate’s sequence and geometry. Ultimately, we aim to inform rational design principles for future device prototyping. For example, one key conclusion of the study is that the high absorbance cross-section and efficient energy transfer observed with rigid substrates made for better photonic antennae, compared to flexible DNA substrates.

Enlarging the Stokes Shift by Weakening the π-Conjugation of Cyanines for High Signal-to-Noise Ratiometric Imaging.

The signal-to-noise ratio (SNR) is one of the key features of a fluorescent probe and one that often defines its potential utility for in vivo labeling and analyte detection applications. Here, it is reported that introducing a pyridine group into traditional cyanine-7 dyes in an asymmetric manner provides a series of tunable NIR fluorescent dyes (Cy-Mu-7) characterized by enhanced Stokes shifts (≈230nm) compared to the parent cyanine 7 dye (<25nm). The observed Stokes shift increase is ascribed to symmetry breaking of the Cy-Mu-7 core and a reduction in the extent of conjugation. The fluorescence signals of the Cy-Mu-7 dyes are enhanced upon confinement within the hydrophobic cavity of albumin or via spontaneous encapsulation within micelles in aqueous media. Utilizing the Cy-Mu-7, ultra-fast in vivo kidney labeling in mice is realized, and it is found that the liver injury will aggravate the burden of kidney by monitoring the fluorescence intensity ratio of kidney to liver. In addition, Cy-Mu-7 could be used as efficient chemiluminescence resonance energy transfer acceptor for the reaction between H2 O2 and bisoxalate. The potential utility of Cy-Mu-7 is illustrated via direct monitoring fluctuations in endogenous H2 O2 levels in a mouse model to mimic emergency room trauma.

Chemiluminescent gels of G-quadruplexes in deep eutectic solvents

Stabilized G-quadruplex systems have focused on biosensors, chromogenic reaction and chemiluminescence (CL) catalysts. On the present, the main studies are building stable G-quadruplexes to form ionogels and improving the performance of circularly polarized luminescence (CPL) or fluorescence resonance energy transfer (FRET). Here, the uncommon G-quadruplexes promoted by deep eutectic solvents (DESs) were established and used for chemiluminescence resonance energy transfer (CRET) platform. The DES containing choline chloride and urea not only provided solvent environment for guanosine but also facilitated the formulation of the aggregates. The ion-dipole interaction among the cation of choline chloride and guanosine gave rise to the G-quartets and the hydrogen bond networks in DES or π-π interaction maintained the stacking G-quartets being G-quadruplexes. Being bound to the hemin endowed G-quadruplexes peroxidase-like properties, which catalyzed the oxidation of luminol and generated expected chemiluminescence. Subsequently, attaching the luminol and fluorescent dyes to the peroxidase-like G-quadruplex/hemin complexes guaranteed the proximity requirements of CRET donor and acceptor. The CRET eutectogels could flash evident blue, chartreuse or cerise light once they were immersed into H2O2 solution, which endowed the eutectogels ability in grouping displaying objects. This work demonstrated the feasibility of simultaneously fixing the donor and acceptor of energy transfer on G-quadruplexes to develop the CRET platform, taking the luminol and dyes as example. And the instant luminescence property expanded the application of eutectogels in pattern visualization field.

Frontispiece: Manipulation of Triplet Excited States in Two‐Component Systems for High‐Performance Organic Afterglow Materials

Recent progress of high-performance afterglow materials obtained by a two-component design strategy is reviewed. Due to the unique advantages of two-component design strategies, various derivative strategies such as the dopant-matrix design, donor–acceptor design, sensitization and energy transfer strategies can be applied to manipulate triplet excited states. This Review article on page 5 ff. presents the latest achievements categorized by different design strategies, discusses the underlying mechanisms, and describes applications of organic afterglow materials in specific areas.

POSS‐based fluorescence sensor for rapid analysis of β‐carotene in health products

In recent years, fluorescent organic-inorganic hybrid nanomaterials have received much interest as potential fluorescent sensor materials. In this study, fluorescent organic-inorganic hybrid nanomaterials (POSS@ANT) were created using polyhedral oligomeric silsesquioxane as the precursor and 9,10-bromoanthracene as the monomer. The morphology and composition of POSS@ANT, as well as its pore characteristics and fluorescence properties were studied. POSS@ANT displayed steady fluorescence emission at an excitation wavelength of 374 nm. Next, a β-carotene fluorescence sensor was developed using the capacity of β-carotene to quench the fluorescence of POSS@ANT. The quenching process is linked to acceptor electron transfer and energy transfer, and the sensor has a high selectivity for β-carotene. This β-carotene fluorescence analysis method that we established has a linear range of 0.2-4.3mg/L and a detection limit of 0.081 mg/L. Finally, it was used to quantify β-carotene in health products, the recovery rate was 91.1-109.9%, the relative standard deviation (RSD) was 2.2-4.3%, and the results were comparable with the results of high-performance liquid chromatography. The approach is reliable and can be used to determine β-carotene in health products.

Vibronic resonance along effective modes mediates selective energy transfer in excitonically coupled aggregates.

We recently proposed effective normal modes for excitonically coupled aggregates that exactly transform the energy transfer Hamiltonian into a sum of one-dimensional Hamiltonians along the effective normal modes. Identifying physically meaningful vibrational motions that maximally promote vibronic mixing suggested an interesting possibility of leveraging vibrational-electronic resonance for mediating selective energy transfer. Here, we expand on the effective mode approach, elucidating its iterative nature for successively larger aggregates, and extend the idea of mediated energy transfer to larger aggregates. We show that energy transfer between electronically uncoupled but vibronically resonant donor-acceptor sites does not depend on the intermediate site energy or the number of intermediate sites. The intermediate sites simply mediate electronic coupling such that vibronic coupling along specific promoter modes leads to direct donor-acceptor energy transfer, bypassing any intermediate uphill energy transfer steps. We show that the interplay between the electronic Hamiltonian and the effective mode transformation partitions the linear vibronic coupling along specific promoter modes to dictate the selectivity of mediated energy transfer with a vital role of interference between vibronic couplings and multi-particle basis states. Our results suggest a general design principle for enhancing energy transfer through synergistic effects of vibronic resonance and weak mediated electronic coupling, where both effects individually do not promote efficient energy transfer. The effective mode approach proposed here paves a facile route toward four-wavemixing spectroscopy simulations of larger aggregates without severely approximating resonant vibronic coupling.

Effect of nanoscale dielectric environments on concentration quenching

Abstract We have studied the dependence of concentration quenching of luminescence (donor–acceptor energy transfer) on the thickness d of dye-doped polymeric films (HITC:PMMA) and found its strong inhibition at small values of d. This phenomenon is tentatively explained by a limited number of acceptors, which donors’ excitation can reach in thin samples, if the film’s thickness is comparable to the diffusion length of the energy transfer. The latter mechanism, along with effective reduction of the dye concentration, is responsible for an inhibition of the concentration quenching of dye molecules impregnating porous alumina membranes. The elongation of emission kinetics in thick (≥3 μm) HITC:PMMA films is cautiously attributed to the samples’ crystallinity.

Excited-State Dynamics of Photoluminescent Gold Nanoclusters and Their Assemblies with Quantum Dot Donors

Gold nanoclusters (AuNCs) are a recently developed class of photoluminescent nanomaterial with potential for detection and imaging applications in both chemistry and biology. The AuNC small size (Au104NC) in combination with their long-lived, near-infrared (NIR) emission suggests that they could be applied as a biological label directly and also as a potential acceptor for energy transfer-based biosensing. Previous studies have shown that functionalized AuNCs can act as energy-transfer acceptors; however, the underlying mechanism appears to be complex and does not necessarily follow a classical Förster process with a (1/R)6 distance dependence. Here, we report a femtosecond and nanosecond time-resolved spectroscopy study to examine the energy dissipation and transfer processes of photoluminescent AuNC acceptors displaying different functionalized end groups and coupled with 625 nm emitting semiconductor quantum dot (QD) donors. Examination of AuNCs alone on the femtosecond timescale show coherent vibrational oscillations within the first 15 ps after excitation in the visible and NIR region. Fourier transform of the kinetic data reveal ∼0.18 and 0.40 THz low-frequency vibrations in aqueous AuNC solutions, with the latter attributed to coherent vibrations following hot electronic relaxation. A biphasic decay of the AuNC excited state on the microsecond timescales confirm their exceptionally long-lived lifetimes and that the photophysics is largely unaffected by the functional end group on the ligand. Finally, ultrafast studies of AuNCs coupled to the 625 QD donors reveal excited-state quenching and wavelength shifts of the QD’s ground-state bleach and the appearance of the excited state of the AuNC resulting from energy transfer occurring on the ∼200 ps timescale.

Graphene Energy Transfer for Single-Molecule Biophysics, Biosensing, and Super-Resolution Microscopy.

Graphene is considered a game-changing material, especially for its mechanical and electrical properties. This work exploits that graphene is almost transparent but quenches fluorescence in a range up to ≈40 nm. Graphene as a broadband and unbleachable energy-transfer acceptor without labeling, is used to precisely determine the height of molecules with respect to graphene, to visualize the dynamics of DNA nanostructures, and to determine the orientation of Förster-type resonance energy transfer (FRET) pairs. Using DNA origami nanopositioners, biosensing, single-molecule tracking, and DNA PAINT super-resolution with <3 nm z-resolution are demonstrated. The range of examples shows the potential of graphene-on-glass coverslips as a versatile platform for single-molecule biophysics, biosensing, and super-resolution microscopy.

Six-in-one peptide functionalized upconversion@polydopamine nanoparticle-based ratiometric fluorescence sensing platform for real-time evaluating anticancer efficacy through monitoring caspase-3 activity

• Six-in-one ratiometric fluorescence sensing platform. • Highly sensitive and selective detection of caspase-3. • The anticancer efficacy evaluation of photothermal (PTT)-chemotherapy. • Real-time noninvasive evaluation of tumor response to PTT and chemotherapy of staurosporine (STS). Herein, a six-in-one peptide functionalized upconversion@polydopamine nanoparticle-based ratiometric fluorescence sensing platform (termed as UCNP@PDA@Cy3-pep) has been fabricated for monitoring the anticancer efficacy of photothermal-chemotherapy in real time through detection of caspase-3 activity. In this work, the upconversion nanoparticle (UCNP) core of UCNP@PDA was employed as an internal reference, while the PDA shell of UCNP@PDA was used as an acceptor of fluorescence resonance energy transfer (FRET) system, photothermal therapy (PTT) agent, loading agent of chemical drug and immobilization platform of Cy3 (donor of FRET) labeled peptide (Cy3-pep), which contains a specific caspase-3 substrate (DEVD) and active tumor-targeting motif (PSP). In the presence of caspase-3, the FRET system was broken through the enzymatic cleavage of DEVD, resulting in a recovery of Cy3 fluorescence emission. Under the optimal conditions, the ratio of recovered Cy3 fluorescence intensity with upconversion luminescent (UCL) intensity was linearly dependent on the caspase-3 concentration within the range of 0.5–50 ng mL −1 and the limit of detection (LOD) was calculated as 0.065 ng mL −1 . Using mouse-bearing MG-63 tumor as a model system, the capability of as-proposed UCNP@PDA@Cy3-pep has been successfully demonstrated through a real-time noninvasive evaluation of tumor response to PTT and chemotherapy of staurosporine (STS).

An exact solution in the theory of fluorescence resonance energy transfer with vibrational relaxation

The elegant expression of Förster that predicts the well-known 1/R6 distance (R) dependence of the rate of energy transfer, although widely used, was derived using several approximations. Notable among them is the neglect of the vibrational relaxation in the reactant (donor) and product (acceptor) manifolds. Vibrational relaxation can play an important role when the energy transfer rate is faster than the vibrational relaxation rate. Under such conditions, donor to acceptor energy transfer can occur from the excited vibrational states. This phenomenon is not captured by the usual formulation based on the overlap of donor emission and acceptor absorption spectra. Here, we develop a Green's function-based generalized formalism and obtain an exact solution for the excited state population relaxation and the rate of energy transfer in the presence of vibrational relaxation. We find that the application of the well-known Förster's expression might lead to overestimation of R.

Near-infrared light excited UCNP-DNAzyme nanosensor for selective detection of Pb2+ and in vivo imaging

Due to similar charges, atomic radii, and chemical properties of most metal ions, the selective sensing of these metal ions and imaging in vivo is still a challenge. A DNAzyme assemblied and near-infrared (NIR) light excited nanosensor was developed to detect and image Pb2+. In this nanosensor, NaYF4:Yb, Er upconversion nanoparticles (UCNPs) introduced as NIR-to-Vis transducer were the donor of luminescence resonance energy transfer (LRET), and DNAzyme-functionalized black hole quencher 1 (BHQ1) acted as energy transfer acceptor. This proposed nanosensor was applied to detecting Pb2+ in solution with high sensitivity and selectivity. Furthermore, we have successfully demonstrated the imaging ability of this nanosensor towords Pb2+ in living cells and early-stage zebrafish with negligible autofluorescence and good photostability. The UCNP-DNAzyme nanosensor would enrich the method of imaging Pb2+ in vivo, and might serve as a potential tool for understanding the metabolic pathways of Pb2+ and the mechanism of lead poisoning in biological system.

Modelling Förster resonance energy transfer (FRET) using anisotropy resolved multi-dimensional emission spectroscopy (ARMES)

BackgroundFörster Resonance Energy Transfer (FRET) is widely used to study the structure and dynamics of biomolecular systems and also causes the non-linear fluorescence response observed in multi-fluorophore proteins. Accurate FRET analysis, in terms of measuring changes in donor and acceptor spectra and energy transfer efficiency is therefore critical. MethodsWe demonstrate a novel quantitative FRET analysis using anisotropy resolved multidimensional emission spectroscopy (ARMES) in a Human Serum Albumin (HSA) and 1,8-anilinonaphathalene sulfonate (ANS) model. ARMES combines 4D measurement of polarized excitation emission matrices (pEEM) with multivariate data analysis to spectrally resolve contributing fluorophores. Multivariate analysis (Parallel Factor, PARAFAC and restricted Tucker3) was used to resolve fluorophore contributions and for modelling the quenching of HSA emission and the HSA-ANS interactions. ResultspEEM spectra were modelled using Tucker3 which accommodates non-linearities introduced by FRET and a priori chemical knowledge was used to optimise the solution, thus resolving three components: HSA emission, ANS emission from indirect FRET excitation, and ANS emission from direct excitation. Perpendicular emission measurements were more sensitive to indirectly excited acceptor emission. PARAFAC modelling of HSA, donor emission, separated ANS FRET interacting (Tryptophan) and non-interacting (Tyrosine) components. This enabled a new way of calculating quenching constants using the multi-dimensional emission of individual donor fluorophores. ConclusionsFRET efficiency could be calculated using the multi-dimensional, resolved emission of the interacting donor fluorophores only which yielded higher ET efficiencies compared to conventional methods. General significanceShows the potential of multidimensional fluorescence measurements and data analysis for more accurate FRET modelling in proteins.

Controllable and Diversiform Topological Morphologies of Self-Assembling Supra-Amphiphiles with Aggregation-Induced Emission Characteristics for Mimicking Light-Harvesting Antenna.

Controllable construction of diversiform topological morphologies through supramolecular self‐assembly on the basis of single building block is of vital importance, but still remains a big challenge. Herein, a bola‐type supra‐amphiphile, namely DAdDMA@2β‐CD, is rationally designed and successfully prepared by typical host–guest binding β‐cyclodextrin units with an aggregation‐induced emission (AIE)‐active scaffold DAdDMA. Self‐assembling investigation reveals that several morphologies of self‐assembled DAdDMA@2β‐CD including leaf‐like lamellar structure, nanoribbons, vesicles, nanofibers, helical nanofibers, and toroids, can be straightforwardly fabricated by simply manipulating the self‐assembling solvent proportioning and/or temperature. To the best of knowledge, this presented protocol probably holds the most types of self‐assembling morphology alterations using a single entity. Moreover, the developed leaf‐like lamellar structure performs well in mimicking the light‐harvesting antenna system by incorporating with a Förster resonance energy transfer acceptor, providing up to 94.2% of energy transfer efficiency.