Förster Resonance Energy Transfer Research Articles

Photoluminescent Sol‐Gel Glass Constructed via Highly Efficient Förster Resonance Energy Transfer

AbstractPhotoluminescent (PL) solid with color tunability are in high demand for the development of large‐area display and illumination devices. With high transparency, high chemical stability, and mature fabrication, sol‐gel glass is an ideal solid matrix to obtain such materials by chromophore doping. However, it remains a big challenge to obtain sol‐gel glass with high luminous efficiency under a single excitation wavelength. Herein, the construction of highly luminescent sol‐gel glass enabled by Förster resonance energy transfer (FRET) is reported. Branched siloxane is used to modify naphthalene and BODIPY, which led to the formation of blue‐emitting donor (denoted as Si‐Nap) and green‐emitting acceptor (denoted as Si‐BODIPY), respectively. Efficient FRET occurs between Si‐Nap and Si‐BODIPY proved by spectral titration and lifetime measurements, with an energy transfer efficiency (ΦET) up to 97.9%. When RhB is added, it acts as a final acceptor that enables the occurrence of a sequential FRET from Si‐Nap to Si‐BODIPY and further to RhB. The overall energy transfer efficiency reaches 94%, and the fluorescence quantum yield exceeds 88%. By adjustment of the composition, color‐tunable sol‐gel glass is obtained with emergence of white‐emitting samples, opening potential applications in a variety of fields.

Förster Resonance Energy Transfer in Metal Halide Perovskite: Current Status and Future Prospects.

Förster Resonance Energy Transfer (FRET) is a non-radiative energy transfer process in a donor-acceptor system and has applications in various fields, such as single-molecule investigations, biosensor creation, and deoxyribonucleic acid (DNA) mechanics research. The investigation of FRET processes in metal halide perovskites has also attracted great attention from the community. The review aims to provide an up-to-date study of FRET in the context of perovskite systems. First, we discuss the fundamentals of FRET process, and then summarize the recent progress of FRET phenomenon in perovskite-perovskite, perovskite-inorganic fluorophores, perovskite-organic fluorophores, and organic fluorophores-perovskite systems. Finally, we speculate on the future prospects of roles of FRET in the implications for the overall performance of optoelectronic devices based on these systems, as well as the challenges in maximizing FRET efficiency.

Effect of Confinement on the Translational Diffusivity of Small Dye Molecules in Thin Polystyrene Films and Its Connection to Tg-Confinement and Fragility-Confinement Effects.

Using fluorescence, we study the impact of nanoscale confinement on the translational diffusivity (D) of trace levels of a small-molecule dye, 9,10-bis(phenylethynyl)anthracene (BPEA), in supported polystyrene (PS) films via Förster resonance energy transfer (FRET). Reductions in BPEA diffusivity are observed in films thinner than ∼200 nm, with D decreasing by 80-90% in 100 nm-thick films compared to bulk. The activation energy of BPEA diffusivity increases from ∼210 kJ/mol in bulk films to ∼370 kJ/mol in 130 nm-thick films. BPEA exhibits a greater diffusivity-confinement effect than a larger dye, decacyclene, in terms of the length scale at which the effects of confinement become evident and the percentage reduction in diffusivity. For both BPEA and decacyclene, the diffusivity-confinement effect in supported PS films occurs at a length scale much larger than that for the glass transition temperature (Tg)-confinement effect and somewhat larger than that for the fragility-confinement effect. This difference in confinement-effect length scales can be rationalized as follows: small-molecule dye diffusivity relates predominantly to short times in the α-relaxation distribution, whereas Tg relates to long times in the α-relaxation distribution, and fragility reflects the overall breadth of this relaxation time distribution. If confinement results in a narrower relaxation time distribution in PS films with the short-time relaxations being shifted to longer times and the longest-time relaxation regimes being shifted to shorter times, then Tg, diffusivity, and fragility all decrease at sufficient levels of confinement. If the narrowing with confinement begins with the shortest relaxation time regimes, then fragility and small-molecule dye diffusivity are influenced by confinement at larger length scales than Tg.

RhB intercalated Zr(VI)-bipyridine architecture for efficient ratiometric fluorescent response toward Cr(VI) analyte and decontamination of Cr(VI) and reactive dye via photochemical REDOX

It is extremely‌ imperative to enhance the sensing accuracy of water-stable Zr-MOFs for Cr(VI), because the single emission signal in a sole Zr-MOF is rather vulnerable to external factors. Interpolation of guest luminous species into Zr-MOF crystals presents a feasible way to achieve dual-emission signals. In this contribution, a highly water-stable Zr-MOF (Zr-bcu-22bipy44dc) which emits bright-blue fluorescence was deployed as matrix to intercalate fluorochrome Rhodamine B (RhB), creating a novel dual-emission (at 410 and 580 nm) luminescent platform, RhB@Zr-MOF. Then, it was utilized as a fluorescence probe to accurately detect trace-level Cr(VI) ions, by assessing the relative fluorescence intensity (IR) difference between the host Zr-MOF (I410) and the guest RhB (I580). Interestingly, the septal interpolation of luminescent species within Zr-MOF matrix effectively suppresses aggregation-induced quenching (ACQ), which tends to occur easily for RhB molecules. Moreover, its determined detection limits (DL) for CrO42- (6.13 ppb) and Cr2O72- (10.04 ppb) ions have been remarkably enhanced by approximately 4.92-fold and 3.66-fold, respectively, compared to the initial Zr-MOF (30.11 and 36.76 ppb). DFT and TD-DFT calculations have confirmed that the orange-yellow photoluminescence exhibited by RhB@Zr-MOF should be attributed to the PET process inherent to the intercalated RhB molecules, rather than the commonly accepted intermolecular Förster resonance energy transfer (FRET) mechanism or the photo-induced electron transfer (PET) effect previously identified by us. Efficient antenna effect of RhB module synergizes with Zr-MOF's appropriate band structure, also enables RhB@Zr-MOF convincing ability to photochemically deoxidize Cr(VI) and bleach reactive dark blue K-R (K-R)

Construction of starch-based room temperature phosphorescence materials with wide color-tunable long afterglow and even persistent near-infrared luminescence via Förster resonance energy transfer

Environmentally friendly natural polymer-based room temperature phosphorescence (RTP) materials exhibit promising applications in anti-counterfeiting and information encryption. However, the construction of natural polymer-based RTP materials with multicolor long afterglow and even persistent near-infrared (NIR) luminescence remains a tough challenge. Here, starch (S)-based ultralong RTP materials with wide color-tunability, persistent NIR luminescence are conveniently prepared through Förster resonance energy transfer (FRET) strategies. The binary doping system S-4-carboxyphenylboric acid with an ultralong phosphorescence lifetime of up to 449 ms is used as energy donor, and commercial dyes fluorescein, rhodamine 6G and lissamine rhodamine B (LRB) are selected as energy acceptors. By adjusting the weight ratio of energy donor and acceptor, tunable multicolor long afterglow from blue to yellow-green, purple, red and even nearly white (0.32, 0.33) can be successfully achieved through the triplet-to-singlet FRET process. The quaternary doping system displays persistent NIR luminescence band from 650 to 800 nm along with the longest phosphorescence lifetime of up to 131 ms via the stepwise FRET process using LRB as the intermediate energy acceptor and NIR dye Nile blue A as the energy acceptor. Satisfactorily, the prepared S-based RTP materials with wide-range color-tunable long afterglow demonstrate potential applications in multimode information encryption and anti-counterfeiting.

Improving performance of CdSe/ZnS QDs via enhancing förster resonance energy transfer and suppressing auger recombination

In quantum dots (QDs) systems, Förster resonance energy transfer (FRET) and Auger recombination (AR) processes are crucial mechanisms that significantly impact their photoluminescence (PL) performance. Developing a strategy to simultaneously enhance FRET process and suppress the AR process is crucial. In this study, we reported that FRET process was enhanced, and the AR process was suppressed in the carbon-CdSe/ZnS QDs system via increasing carbon QDs donor ratios. The enhanced FRET rate is assigned to the increased adsorbed numbers and shortened donor-acceptor distance. The reduced AR rate is assigned to the decoration of the surface for CdSe/ZnS QDs acceptor in increased adsorbed numbers. As a result, the PL intensity of CdSe/ZnS QDs acceptor increased by over 3-fold. Our findings will stimulate the development of highly defined cascaded energy-transfer structures, aiming to achieve high-performance light-emitting devices.

Synergistic enhancement of photoluminescence and advanced deep learning model through YOLOv8x in combined effects of carbon dots and Sr₉Al₆O₁₈:Sm³⁺ phosphors

A series of orange-red-emitting Sr₉Al₆O₁₈:Sm³⁺ (1–11 mol %) phosphors are synthesized using the combustion method, while carbon dots (CDs) are produced from urea and citric acid. The incorporation of CDs into the Sr₉Al₆O₁₈:Sm³⁺ (SAO:Sm3+) matrix reduced both negative and positive defects, enhancing the crystallinity of the phosphor. A significant spectral overlap is observed between the emission of CDs and the absorption of SAO:Sm³⁺. An 11.9-folds enhancement in luminescence intensity is detected from the 5 wt% CDs@SAO:Sm³⁺ composite, along with an extended fluorescence lifetime. The energy transfer between CDs and Sm³⁺ is demonstrated, with the increased PL intensity attributed to the Förster Resonance Energy Transfer (FRET) mechanism. The CDs@SAO:Sm³⁺ composites demonstrated excellent selectivity and high contrast when developing latent fingerprints (LFPs). Level I–III structural characteristics of LFPs are easily recognized under ulta violet (UV) light. Furthermore, YOLOv8x, an effective deep learning model, has been modified for the important forensic science task of LFPs recognition. YOLOv8x is able to precisely locate LFPs in complex backgrounds by employing the real-time object detection capabilities of the architecture. With this adjusting, detection speed and accuracy are much increased, making it an effective tool for forensic analysis and law enforcement applications. The optimized orange-red-emitting CDs@SAO:Sm³⁺ composites is synthesized with soluble polyvinyl alcohol (PVA) to produce a transparent anti-counterfeiting ink. The resulting film exhibited excellent flexibility, foldability, and superior thermal and optical properties. In summary, the highly efficient CDs@SAO:Sm³⁺ composite is a versatile luminescent material with multifunctional capabilities, making it ideal for flexible films, LFPs detection, and white light-emitting diodes (w-LEDs) applications.

Design and Construction of an Artificial Light‐Harvesting System Based on Polyacrylic Acid and a Cyanostilbene Derivative

AbstractThe development of materials with tunable fluorescence properties is critical for advancing applications in sensing, imaging, and information encryption. In this study, we synthesized a cyanostilbene derivative (CSA) that combines the benefits of aggregation‐induced emission (AIE) and self‐assembly in water. CSA, featuring a cyanostilbene core and hydrophilic carboxylate groups, exhibits weak fluorescence in solution but forms highly fluorescent nanoaggregates (CSA‐PAA) upon self‐assembly with polyacrylic acid (PAA). By integrating rhodamine 6G (Rh6G) as an energy acceptor, we constructed a light‐harvesting system (CSA‐PAA‐Rh6G) with high Förster resonance energy transfer (FRET) efficiency and tunable emission from green to yellow. This work presents a facile approach for the development of aqueous light‐harvesting systems and shows promise for future applications in tunable luminescent materials.

Fluorescence Lifetime Imaging for Quantification of Targeted Drug Delivery in Varying Tumor Microenvironments.

Trastuzumab (TZM) is a monoclonal antibody that targets the human epidermal growth factor receptor 2 (HER2) and is clinically used for the treatment of HER2-positive breast tumors. However, the tumor microenvironment can limit the access of TZM to the HER2 targets across the whole tumor and thereby compromisingTZM's therapeutic efficacy. An imaging methodology that can non-invasively quantify the binding of TZM-HER2, which is required for therapeutic action, and distribution within tumors with varying tumor microenvironments is much needed. Near-infrared (NIR) fluorescence lifetime (FLI) Forster Resonance Energy Transfer (FRET) is performed to measure TZM-HER2 binding, using in vitro microscopy and in vivo widefield macroscopy, in HER2 overexpressing breast and ovarian cancer cells and tumor xenografts, respectively. Immunohistochemistry is used to validate in vivo imaging results. NIR FLI FRET in vitro microscopy data show variations in intracellular distribution of bound TZM in HER2-positive breast AU565 and AU565 tumor-passaged XTM cell lines in comparison to SKOV-3 ovarian cancer cells. Macroscopy FLI (MFLI) FRET in vivo imaging data show that SKOV-3 tumors display reduced TZM binding compared to AU565 and XTM tumors, as validated by ex vivo immunohistochemistry. Moreover, AU565/XTM and SKOV-3 tumor xenografts display different amounts and distributions of TME components, such as collagen and vascularity. Therefore, these results suggest that SKOV-3 tumors are refractory to TZM delivery due to their disrupted vasculature and increased collagen content. The study demonstrates that FLI is a powerful analytical tool to monitor the delivery of antibodydrugs both in cell cultures and in vivo live systems. Especially, MFLI FRET is a unique imaging modality that can directly quantify target engagement with the potential to elucidate the role of the TME in drug delivery efficacy in intact live tumor xenografts.

Ultrahighly-efficient and stable luminescent solar concentrators enabled by FRET-based carbon nanodots

Luminescent solar concentrators (LSCs) as an optical device to concentrate light from large areas illuminated by sunlight into small-area photovoltaic cells, can greatly reduce the cost of solar energy generation, thus showing promise in building-integrated photovoltaics. Here, we report the synthesis of a novel type of composite nanoparticle via the simple sol-gel method. Starting from hydroxyl-rich carbon nanodots (CDs), Rhodamine B (RhB) molecules were embedded into a silica matrix shell, forming a composite core-shell system, where the CDs represent the core and RhB embedded in SiO2 are the shell of the final CDs/RhB@SiO2 structure. These nanoparticles were successfully employed in high-performance LSC fabrication. The Förster resonant energy transfer (FRET) between the CDs and the dye was successfully exploited to improve the light absorption efficiency and power conversion efficiency (ηPCE) of LSC devices. The solid-state photoluminescence quantum yield of the as-synthesized composite nanoparticles can reach ∼ 57 % due to the effective suppression of the aggregation-induced quenching. These fluorescent composite nanoparticles were used for fabricating LSC devices with an ultrahigh ηPCE of ∼ 3.8 % for 5 × 5 cm2 devices, thanks to the high loading of luminophores and effective FRET.

In-situ oxidative polymerization of dopamine triggered by CuO2 in acidic condition and application in "turn-off" sensing.

Dopamine (DA) is a key neurotransmitter whose concentration affects various neurological disorders. Unlike previous methods that synthesize non-fluorescent polydopamine (NFL-PDA) under alkaline conditions, this study introduces a novel "turn-off" sensing method for DA using NFL-PDA synthesized through a unique reaction pathway. In our approach, CuO2 nanodots, created via a simple reduction method, catalyze the formation of hydroxyl radicals (•OH) in acidic conditions, triggering the oxidative polymerization of DA into NFL-PDA. The reaction between DA and CuO2 nanodots in acidic solution was examined to understand the process. UiO-66-NH2 was then used to test NFL-PDA's fluorescence quenching ability and to further investigate the DA determination mechanism. Results showed that fluorescence quenching was due to enhanced non-radiative energy transfer and Förster resonance energy transfer (FRET) between NFL-PDA and UiO-66-NH2. This led to the development of a simple "turn-off" fluorometric DA determination method with a linear range of 0.1-200μmol/L and a limit of detection (LOD) of 0.0575μmol/L. Although this method does not outperform existing NFL-PDA synthesis methods under alkaline conditions, it provides a new synthesis approach and application for sensing DA, contributing to the basic theory of chemical sensing. Additionally, DA determination in human serum samples was successfully achieved, with results consistent with high-performance liquid chromatography (HPLC).

The cell adhesion molecule CD44 acts as a modulator of 5-HT7 receptor functions

BackgroundHomo- and heteromerization of G protein-coupled receptors (GPCRs) plays an important role in the regulation of receptor functions. Recently, we demonstrated an interaction between the serotonin receptor 7 (5-HT7R), a class A GPCR, and the cell adhesion molecule CD44. However, the functional consequences of this interaction on 5-HT7R-mediated signaling remained enigmatic.MethodsUsing a quantitative FRET (Förster resonance energy transfer) approach, we determined the affinities for the formation of homo- and heteromeric complexes of 5-HT7R and CD44. The impact of heteromerization on 5-HT7R-mediated cAMP signaling was assessed using a cAMP responsive luciferase assay and a FRET-based cAMP biosensor under basal conditions as well as upon pharmacological modulation of the 5-HT7R and/or CD44 with specific ligands. We also investigated receptor-mediated G protein activation using BRET (bioluminescence resonance energy transfer)-based biosensors in both, homo- and heteromeric conditions. Finally, we analyzed expression profiles for 5-HT7R and CD44 in the brain during development.ResultsWe found that homo- and heteromerization of the 5-HT7R and CD44 occur at similar extent. Functionally, heteromerization increased 5-HT7R-mediated cAMP production under basal conditions. In contrast, agonist-mediated cAMP production was decreased in the presence of CD44. Mechanistically, this might be explained by increased Gαs and decreased GαoB activation by 5-HT7R/CD44 heteromers. Unexpectedly, treatment of the heteromeric complex with the CD44 ligand hyaluronic acid boosted constitutive 5-HT7R-mediated cAMP signaling and receptor-mediated transcription, suggesting the existence of a transactivation mechanism.ConclusionsInteraction with the hyaluronan receptor CD44 modulates both the constitutive activity of 5-HT7R as well as its agonist-mediated signaling. Heteromerization also results in the transactivation of 5-HT7R-mediated signaling via CD44 ligand.

Stereospecific Properties and Intracellular Transport of Novel Intrinsically Fluorescent Neurosteroids.

Allopregnanolone (AlloP) is an example of neuroactive steroids (NAS), which is a potent allosteric activator of the γ-aminobutyric acid A (GABAA) receptor. The mechanisms underlying the biological activity of AlloP and other NAS are only partially understood. Here, we present intrinsically fluorescent analogs of AlloP (MQ-323) and its 3β-epimer, epi-allopregnanolone (E-AlloP) (YX-11), and show, by a combination of spectroscopic and computational studies, that these analogs mimic the membrane properties of AlloP and E-AlloP very well. We found stereospecific differences in the orientation and dynamics of the NAS as well as in their impact on membrane permeability. However, all NAS are unable to condense the lipid bilayer, in stark contrast to cholesterol. Using Förster resonance energy transfer (FRET) and electrophysiological measurements, we show that MQ-323 but not YX-11 binds at the intersubunit site of the ELICα1GABAA receptor and potentiates GABA-induced receptor currents. In aqueous solvents, YX-11 forms aggregates at much lower concentrations than MQ-323, and loading both analogs onto cyclodextrin allows for their uptake by human astrocytes, where they become enriched in lipid droplets (LDs), as shown by quantitative fluorescence microscopy. Trafficking of the NAS analogs is stereospecific, as uptake and lipid droplet targeting is more pronounced for YX-11 compared to MQ-323. In summary, we present novel minimally modified analogs of AlloP and E-AlloP, which enable us to reveal stereospecific membrane properties, allosteric receptor activation, and intracellular transport of these neurosteroids. Our fluorescence design strategy will be very useful for the analysis of other NAS in the future.

Fast and accurate multi-bacterial identification using cleavable and FRET-based peptide nucleic acid probes

Fast and accurate identification of pathogenic microbes in patient samples is crucial for the timely treatment of acute infectious diseases such as sepsis. The fluorescence in situ hybridization (FISH) technique allows the rapid detection and identification of microbes based on their variation in genomic sequence without time-consuming culturing or sequencing. However, the recent explosion of microbial genomic data has made it challenging to design an appropriate set of probes for microbial mixtures. We developed a novel set of peptide nucleic acid (PNA)-based FISH probes with optimal target specificity by analyzing the variations in 16S ribosomal RNA sequence across all bacterial species. Owing to their superior penetration into bacteria and higher mismatch sensitivity, the PNA probes distinguished seven bacterial species commonly observed in bacteremia with 96–99.9% accuracy using our optimized FISH procedure. Detection based on Förster resonance energy transfer (FRET) between pairs of adjacent binding PNA probes eliminated crosstalk between species. Rapid sequential species identification was implemented, using chemically cleavable fluorophores, without compromising detection accuracy. Owing to their outstanding accuracy and enhanced speed, this set of techniques shows great potential for clinical use.

Unleashing Giant Förster Resonance Energy Transfer by Bound State in the Continuum.

Förster resonance energy transfer (FRET), driven by dipole-dipole interactions (DDIs), is widely utilized in chemistry, biology, and nanophotonics. However, conventional FRET is ineffective at donor-acceptor distances exceeding 10 nm and measurements suffer from low signal-to-noise ratios. In this study, we demonstrate significant FRET enhancement and extended interaction distances under ambient conditions by utilizing a bound state in the continuum (BIC) mode within a dielectric metasurface cavity. This enhancement is achieved by leveraging the ultrahigh quality factors, minimal material absorption, and nonlocal effects associated with the BIC mode. Spectrally and angularly resolved photoluminescence (PL) lifetime measurements reveal that the BIC mode significantly increases the FRET rate and interaction distance. The FRET rate is enhanced by up to 70-fold, and the interaction distance is significantly boosted by over an order of magnitude, reaching ∼100 nm. These findings offer valuable insights for achieving long-range, high-efficiency FRET and collective DDIs using loss-less dielectric metasurfaces.

TADF‐Emitting Nanoparticles for Application as Probes in Time‐Resolved Imaging and 1O2 Photosensitizers

AbstractOrganic Thermally Activated Delayed Fluorescence (TADF) molecules are luminescent compounds capable of harvesting energy from triplet states without using heavy metals. This process results in oxygen‐sensitive, long‐lived delayed emission, suitable for developing optical probes for time‐gated cell imaging, oxygen sensors, and singlet oxygen photosensitizers. Despite their potential, the use of TADF emitters in these applications is hindered by poor performance in polar media and the challenge of balancing high photoluminescence quantum yields, long emission lifetimes, and high triplet formation quantum yields. In this study, novel TADF emitters are developed based on 1,8‐naphthalimide (NI) dyes, and how encapsulation in polymeric nanoparticles can enhance their performance in aqueous media is demonstrated. The resulting nanomaterials exhibit high delayed‐to‐prompt emission ratios, long delayed fluorescence lifetimes, and exceptional applicability in time‐resolved imaging. The singlet oxygen photosensitization capabilities of the TADF nanomaterials in the photodegradation of phenol, exploring a Förster Resonance Energy Transfer (FRET) system that improved the efficiency, are also assessed. These findings highlight the promising potential of TADF nanomaterials for diverse applications, including photodegradation of pollutants, cellular imaging, and biosensing.

Fluorometric detection of quinolones via AIE and FRET with terbium-doped carbon dots and copper nanoclusters

Terbium and nitrogen co-doped carbon dots (Tb@N-CDs), combined with α-lipoic acid-functionalized copper nanoclusters (LA@CuNCs), were proposed for the ratiometric detection of quinolone (QA) antibiotics. In this system, Tb@N-CDs facilitate the aggregation of LA@CuNCs, enhancing its fluorescence emission at 670 nm via aggregation-induced emission enhancement (AIEE). Meanwhile, the fluorescence emission of Tb@N-CDs at 460 nm diminishes due to Förster resonance energy transfer (FRET). Upon the introduction of QA, the binding between Tb3+ ions and N-CDs weakens, disrupting both AIEE and FRET processes. This disruption results in a reduction in fluorescence emission at 670 nm and a concurrent increase at 460 nm. The fluorescence response ratio (F460/F670) increases with higher concentrations of ciprofloxacin (CFX), demonstrating a linear range from 0.008 to 120 μmol L−1 and LOD of 1.6 nmol L−1. The method successfully detected CFX in milk and urine samples, achieving recoveries between 97.7 % and 103.8 %, RSD of less than 3.79 %.

Identifying the minimal sets of distance restraints for FRET-assisted protein structural modeling.

Proteins naturally occur in crowded cellular environments and interact with other proteins, nucleic acids, and organelles. Since most previous experimental protein structure determination techniques require that proteins occur in idealized, non-physiological environments, the effects of realistic cellular environments on protein structure are largely unexplored. Recently, Förster resonance energy transfer (FRET) has been shown to be an effective experimental method for investigating protein structure in vivo. Inter-residue distances measured in vivo can be incorporated as restraints in molecular dynamics (MD) simulations to model protein structural dynamics in vivo. Since most FRET studies only obtain inter-residue separations for a small number of amino acid pairs, it is important to determine the minimum number of restraints in the MD simulations that are required to achieve a given root-mean-square deviation (RMSD) from the experimental structural ensemble. Further, what is the optimal method for selecting these inter-residue restraints? Here, we implement several methods for selecting the most important FRET pairs and determine the number of pairs that are needed to induce conformational changes in proteins between two experimentally determined structures. We find that enforcing only a small fraction of restraints, , where is the number of amino acids, can induce the conformational changes. These results establish the efficacy of FRET-assisted MD simulations for atomic scale structural modeling of proteins in vivo.

Fluorescent Sensing for the Detection and Quantification of Sulfur-Containing Gases.

Sulfur-containing gases, such as H2S and SO2, play significant roles in a multitude of biological processes affecting human life and health. Precise and efficient detection of these gases is therefore crucial for advancing one's understanding of their biological roles and developing effective diagnostic strategies. Fluorescent sensing offers a highly sensitive and versatile approach for detecting these gases. This Review examines the recent advances in the fluorescent detection of H2S and SO2, highlighting the key mechanisms involved in fluorescence signal transduction, including changes in intensity and wavelength shifts. The diverse array of probe molecules employed for this purpose, including those utilizing mechanisms such as nucleophilic reactions, Förster resonance energy transfer (FRET), and sulfur affinity interactions are explored. In additional to organic sensors, the focus of the Review is particularly directed toward quantum dot (QD) systems, emphasizing their tunable optical properties that hold immense potential for fluorescence sensing. Beyond the traditional III-V QDs, we delve into the emerging fluorescence sensors based on halide perovskite QDs, upconversion nanocrystals, and other novel materials. These advanced QD systems hold promise for the development of highly sensitive and cost-effective gas detectors, paving the way for significant advances in biomedical and environmental monitoring. This Review provides a comprehensive overview of the current state-of-the-art in QD-based fluorescence sensing of sulfur-containing gases and provides a multifaceted discussion comparing organic fluorescent sensors with QD sensors, highlighting the key challenges and opportunities for the integration of fluorescence sensing as it evolves. The Review aims to facilitate further research and development of innovative sensing platforms to enable more accurate and sensitive detection of these important gases.

MotY modulates proton-driven flagellar motor output in Pseudomonas aeruginosa

MotY homologs are present in a variety of monotrichous bacterial strains and are thought to form an additional structural T ring in flagellar motors. While MotY potentially plays an important role in motor torque generation, its impact on motor output dynamics remains poorly understood. In this study, we investigate the role of MotY in P. aeruginosa, elucidating its interactions with the two sets of stator units (MotAB and MotCD) using Förster resonance energy transfer (FRET) assays. Employing a newly developed bead assay, we characterize the dynamic behavior of flagellar motors in motY mutants, identifying MotY as the key functional protein to affect the clockwise bias of naturally unbiased motors in P. aeruginosa. Our findings reveal that MotY enhances stator assembly efficiency without affecting the overall assembly of the flagellar structure. Additionally, we demonstrate that MotY is essential for maintaining motor torque and regulating switching rates. Our study highlights the physiological significance of MotY in fine-tuning flagellar motor function in complex environments.