High Forster Resonance Energy Transfer Research Articles

A New BODIPY Material for Pure Color and Long Lifetime Red Hyperfluorescence Organic Light-Emitting Diode.

A red fluorescent material, 1,3,7,9-tetrakis(4-(tert-butyl)phenyl)-5,5-difluoro-10-(2-methoxyphenyl)-5H-4l4,5l4-dipyrrolo[1,2-c:2',1'-f][1,3,2]diazaborinine (4tBuMB), as an emitting dopant in a thermally activated delayed fluorescence (TADF) sensitized hyperfluorescence organic light-emitting diode (HFOLED) is reported. The 4tBuMB shows a high photoluminescence quantum yield (PLQY) of 99% with an emission maximum at 620 nm and a full width at half-maximum (fwhm) of 31 nm in solution. Further, it shows a deep lowest unoccupied molecular orbital (LUMO) of 3.83 eV. Thus, two TADF materials, 4CzIPN and 4CzTPN, as sensitizing hosts, are selected on the basis of a suitable LUMO level and spectrum overlap with 4tBuMB. The fabricated HFOLED device with 4CzTPN as a sensitizing host and 4tBuMB as an emitting dopant shows a maximum external quantum efficiency (EQE), an emission maximum, an fwhm, and CIE coordinates of 19.4%, 617 nm, 44 nm, and (0.64, 0.36), respectively. The electroluminance performances of the 4CzTPN sensitized device are higher than those of the 4CzIPN-based device, which is attributed to a higher Förster resonance energy transfer (FRET) rate and reduced intersystem crossing/reverse intersystem crossing (ISC/RISC) cycles of the former. Also, the 4CzTPN-based HF device shows a longer device lifetime (LT90) of 954 h than the 4CzIPN-baed device (LT90 of 57 h) at 3000 cd m-2. The higher device stability is due to the higher bond dissociation energies (BDEs) of 4CzTPN and 4tBuMB than that of 4CzIPN.

Nucleolin-Targeted DNA Nanotube for Precise Cancer Therapy through Förster Resonance Energy Transfer-Indicated Telomerase Responsiveness.

Precise drug delivery holds great promise in cancer treatment but still faces challenges in controllable drug release in tumor cells specifically. Herein, a nucleolin-targeted and telomerase-responsive DNA nanotube for drug release was developed. First, a DNA nanosheet with four capture strands on its surface was prepared, which could bind and load ricin A chain (RTA). The RTA-loaded nanosheet was further converted into a DNA nanotube with a high Förster resonance energy transfer (FRET) efficiency in the presence of a Cy3-modified DNA fastener by hybridizing with the Cy5-modified DNA and another DNA-containing telomerase primer sequence along the long sides. Moreover, the aptamer of nucleolin was assembled on the DNA nanotube by combining with the hybrid chain at the terminal. The aptamer-functionalized and RTA-loaded DNA nanotube displayed enhanced tumor permeability and precise drug release in response to the telomerase in tumor cells, following the change of the FRET signal and RTA-induced cell death. Moreover, the DNA nanotube was applied successfully in vivo, and there was an obvious inhibition of tumor growth on xenograft-bearing mice following systemic administration, indicating that the constructed DNA nanotube represents a promising platform for precise RTA delivery in target cancer therapy.

Dye-Loaded Quatsomes Exhibiting FRET as Nanoprobes for Bioimaging.

Fluorescent organic nanoparticles (FONs) are emerging as an attractive alternative to the well-established fluorescent inorganic nanoparticles or small organic dyes. Their proper design allows one to obtain biocompatible probes with superior brightness and high photostability, although usually affected by low colloidal stability. Herein, we present a type of FONs with outstanding photophysical and physicochemical properties in-line with the stringent requirements for biomedical applications. These FONs are based on quatsome (QS) nanovesicles containing a pair of fluorescent carbocyanine molecules that give rise to Förster resonance energy transfer (FRET). Structural homogeneity, high brightness, photostability, and high FRET efficiency make these FONs a promising class of optical bioprobes. Loaded QSs have been used for in vitro bioimaging, demonstrating the nanovesicle membrane integrity after cell internalization, and the possibility to monitor the intracellular vesicle fate. Taken together, the proposed QSs loaded with a FRET pair constitute a promising platform for bioimaging and theranostics.

Quantum Dots Improve Photovoltaic Properties of Purple Membranes under Near-Infrared Excitation

Purple membrane (PMs), in which the photosensitive protein bacteriorhodopsin (bR) naturally occurs, have photovoltaic properties and are promising for optoelectronic applications. However, PMs cannot effectively absorb light in the NIR spectral region. Semiconductor quantum dots (QDs), which have high two-photon absorption cross-sections in the NIR region, can significantly improve the light sensitivity of PMs by means of Forster resonance energy transfer (FRET) from QDs to bR inside PMs. The purpose of this study was to improve the photovoltaic properties of PMs by means of FRET from QDs to bR under NIR two-photon excitation. We made the QD-PM complexes and showed high FRET efficiency in them. Finally, we found that the current signal from the QD-PM material was higher than that in the case of PMs alone under NIR excitation. The obtained results clearly demonstrate improvement of the photovoltaic properties of PMs under NIR two-photon excitation due to the FRET from QDs to bR and show the prospect of designing new photosensitive bio-nanohybrid devices.

Photophysical Probing of Dye Microenvironment, Diffusion Dynamics, and Energy Transfer

The objective of this work was to apply an organic dye, tetraphenylporphrin (TPP), to probe the aggregation state, microviscosity, and diffusion dynamics of dye molecules within the interior microenvironment of conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(2,5-p-xylene)] nanoparticles (PFX NPs) which should open up further prospects in designing new porphyrin based nanoparticle materials and improve the knowledge of the better design of the nanophotonic devices based on dye-doped polymer NPs. This designed, aggregation-free TPP-doped PFX NPs system, exhibited remarkably high Forster resonance energy transfer (FRET) efficiency, leading to a potential application as a light harvesting system or a loadable drug carrier. To this end, different concentrations of TPP were doped into PFX NPs, prepared using a reprecipitation method. To compare TPP in organic solvent with TPP within the NP microenvironment, a successful doping of TPP into PFX NPs and no TPP aggregation formed inside of the NPs were ...

NIR-responsive DNA hybridization detection by high efficient FRET from 10-nm upconversion nanoparticles to SYBR green I

Abstract A near-infrared (NIR) responsive DNA probe has been developed for DNA hybridization detection with characteristics of high efficient Forster resonance energy transfer (FRET) from small (∼10 nm) upconversion nanoparticles (UCNPs) to nucleic acid stain SYBR Green I (SG, a specific intercalator of double-stranded DNA). The positively charged UCNPs were prepared and facilely attached with single DNA strands by coordination interaction, which acted as probes to detect the DNA targets in the presence of SG. This probe possesses not only the superiority of the NIR-excitation nature of UCNPs which could minimize the autofluorescence background from biomolecules and the photodamage to biological specimens, but also the advantages of facile preparation and high FRET signals. The FRET efficiencies could increase significantly from 2.6% to 12.5% and then to 26% when the size of UCNPs reduced from 94 nm to 30 nm and to 10 nm, respectively. The 10 nm-UCNP-based DNA probe could reach a lower detection limit of complementary ssDNA2 at 3.2 nM and three-base mismatched ssDNA2-M3 at 7.6 nM. The high sensitivity and selectivity of the probe may endow the system with great potential in fluorescence-based biosensing under the irradiation of NIR light.

Sub-Millisecond Unfolding Kinetic Spectra Reveals Intermediate Transitions

The formation of stable partially folded structures on the folding pathway of a protein plays an important role for its correct function. Intermediate states mediate protein (sub-) domain folds to reach the most stable native conformational state. Serious diseases can be triggered if proteins are incorrectly folded stabilizing misfolded conformational states. Currently, no single biophysical tool exist that could provide the overall map all conformational transitions during fondling or unfolding kinetics. Here, we used the model enzyme lysozyme from the phage T4 (T4L), a simple two-subdomain protein, from which is known from prior NMR and stopped-flow experiments that it unfolds via at least two intermediate states. To complete the kinetic gap, we created a library of double mutants of the cysteine-free pseudo-wild type by inserting an unnatural amino acid and a cysteine mutation. We proceeded to site-specifically labeled them using orthogonal chemistry with a Forster resonance energy transfer (FRET) dye pair to build up a network of distance restrains spanning the enzyme. The unfolding process was monitored using traditional ensemble methods like CD- spectroscopy and fluorescence spectroscopic methods (ensemble time correlated single photon counting, single molecule fluorescence spectroscopy, (filtered) fluorescence correlation spectroscopy). Single molecule high precision FRET, with its high temporal and spatial resolution, covering over seven orders of magnitude on time, enables us to determine equilibrium transition rates between conformational states in denatured conditions. By using a priori knowledge from earlier studies, we are able to assign the formerly unknown rates to the folding and unfolding intermediate formation steps. The previously reported millisecond process, belonging to the interconversion of both intermediates, can be observed in our single-molecule multiparameter fluorescence detection histograms.

Deciphering Folding Pathways of Phage T4 Lysozyme: Influence of Multiple Conformations

Understanding how a linear strand of amino acids folds into an active protein in the cell is still one of the challenges in biochemistry. Moreover, as quite a distinct amount of misfolded proteins are responsible for diseases, e. g. Alzheimer's. Thus, understanding the folding pathway, hence describing the energy landscape, of a protein is of critical importance. Here, we used the model enzyme lysozyme from the phage T4 (T4L), a simple two domain protein, which already exists in an equilibrium of at least three conformations in the folded state, a situation expected from most other proteins as well.Thus, we created a set of double mutants of the cysteine-free pseudo-wild type by inserting an unnatural amino acid and a cysteine mutation, which builds up a network of distances spanning the enzyme. Later, we site-specifically labeled them using orthogonal chemistry with a Forster resonance energy transfer (FRET) dye pair. The unfolding process was monitored on the one hand using traditional ensemble methods like CD- spectroscopy and on the other hand with our fluorescence spectroscopic methods (ensemble steady-state fluorescence, ensemble time correlated single photon counting, single molecule fluorescence spectroscopy, filtered fluorescence correlation spectroscopy). Single molecule high precision FRET, with its high temporal and spatial resolution covering seven time decades, enables us to determine transition rates between conformational states in equilibrium and in denatured conditions. The combination of our fluorescence spectroscopic tool provides enough information to describe the energy landscape of the unfolding process of T4L and its paths to the unfolded conformations.

Accurate Distance and Structure Determination of Three Different RNA Three-Way Junctions via High Precision FRET

RNA three-way junctions are important ribosomal structural motifs. They are also widely used as building blocks and functional components in nanotechnology applications. Forster-Resonance-Energy-Transfer (FRET) restrained high-precision structural modeling in combination with molecular dynamics simulations was used to determine the structure of RNA three-way junction (3WJ) without bulges, RNA three-way junction with a small (two unpaired nucleotides) bulge and RNA three way junction with bigger (5 unpaired nucleotides) bulge. In total 81 Donor-Acceptor pairs were measured using single-molecule multi-parameter fluorescence detection (smMFD). This allows us to observe structural changes of the molecule induced by addition of bulge to the initial structure. Rigid body models for the major conformers were obtained by docking rigid double-stranded A-RNA helices explicitly taking into account dye position distributions. This is done many times (1000 iterations) with random starting conformations, yielding all local minima. Obtained models were then refined by all-atom MD simulations [1,2]. First results indicate the presence of two coaxially stacked helices for 3WJs with additional bulges at the junction, and absence of such stacking in case with no bulge. noteworthy the stacked helices are different for the 3WJs with two and five nucleotides in the bulge.Our studies showed that high precision FRET measurements are a valuable tool to complement the structural information obtained by X-ray crystallography or NMR spectroscopy as these techniques are limited in detecting minority conformers.

The photophysical and energy transfer behaviour of low symmetry phthalocyanine complexes conjugated to coreshell quantum dots: an energy transfer study

Abstract This work reports on the synthesis of new coreshell quantum dots (QDs)-low symmetry phthalocyanines conjugates. The energy transfer from QDs (donor) to phthalocyanines (acceptor) was investigated when the two are mixed together or chemically linked to each other. Ti monocarboxy phthalocyanine QDs-linked and Sn monocarboxy phthalocyanine QDs-linked gave the smallest centre-to-centre separation distance ( r ) corresponding to their higher Forster resonance energy transfer efficiencies which are estimated at 0.76 and 0.85 respectively. Higher energy transfer behaviour was achieved for all the covalently linked conjugates compared to their corresponding mixed counterparts. An improvement in triplet quantum yields and lifetimes was achieved for all the complexes in the presence of quantum dots, with the linked counterparts displaying excellent triplet state behaviour.