Fluorescence Energy Research Articles

Study on the stability of different refractories during the melting process of a K4169 Ni-based superalloy

The composition of the refractory strongly affects the cleanliness of the alloy. K4169 Ni-based superalloys were melted in different types of refractories in this study. The cleanliness of the Ni-based superalloy and phase transformation of the refractory were observed by X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy energy dispersive spectroscopy (SEM‒EDS). The high-temperature stabilities of a Y2O3-based refractory, MgO-based refractory, and Al2O3-based refractory during melting with a Ni-based alloy were compared. The oxygen content was also lowest, and no Y2O3-containing inclusions were observed in the Ni-based alloy melted with the Y2O3-based refractory at 1823 K. Inclusions with 21%–29% MgO and a phase composed of Al, Mg and O with an area of approximately 1300 μm2 were observed in the alloy. This indicates that the dissolution and erosion of the Y2O3-based refractory were weak, and obvious physical erosion and chemical dissolution of the MgO-based refractory occurred during the melting process of the Ni-based alloy. The width of the refractory phase adhered to the boundary of the Ni-based alloy increased in the order Y2O3-based refractory (15 μm- 23 μm)< Al2O3-based refractory (93 μm- 285 μm)< MgO-based refractory (3.5 mm–3.6 mm), indicating that the adhesive strength of the MgO-based refractory with the Ni-based alloy was strongest. The interaction between the refractory material, Ni-based alloy and inclusions was analyzed based on thermodynamic calculations by Factsage software. The effects of dissolution of the three refractory types on the formation and transformation of the new phases and inclusions were estimated. The thermodynamic results were in good agreement with the experimental results.

Exploring fluorescent light energy as management option for canine superficial bacterial folliculitis.

Superficial bacterial folliculitis (SBF) represents a common dermatological diagnosis in dogs that can be successfully managed with either topical and/or systemic treatments. In the present study we evaluated the efficacy of a fluorescent light energy (FLE) device as sole management for SBF. The same FLE device has been shown, as adjunct therapy to systemic antibiotic or alone, to effectively control clinical manifestation of interdigital furunculosis. Twenty dogs were randomized to receive FLE once (six dogs) or twice (six dogs) weekly in comparison with oral anti-biotic (eight dogs) until complete healing. FLE regimen was able to significantly reduce the time needed to clinical resolution for oral antibiotic, supporting owners' compliance and welfare of dogs.

Fluorescent Light Energy (FLE) Generated through Red LED Light and a Natural Photoconverter Gel as a New, Non-Invasive Approach for Facial Age Control: A Pilot Study

This study, for the first time, evaluated the safety and efficacy of a new natural-based topical gel containing a spirulina extract. This photoconverter gel generates fluorescent light energy (FLE) via a red LED light device, which is proven to be effective for age control of facial skin. This was a one-centre, observational, uncontrolled pilot trial. Eight healthy female subjects aged 35 to 65 years old, with Fitzpatrick skin types II–V were recruited. The duration of the study was five treatment sessions of one treatment every seven days, with a final follow-up at one month after the last treatment session. The images and the related data were acquired with the SONY® Mod. DSCRX10M3, the Canfield VISIA Facial Imaging System®, and QUANTIFICARE 3D® analysis. Patient compliance was excellent (100%) and the treatment was described as warm and pleasant by the patients. After 30 days, VISIA parameters such as wrinkles, texture, red areas, and Trueskin Age® had improved. The safety and efficacy of the FLE treatment assessed in this trial were achieved for overall rejuvenation of facial skin, focusing on wrinkles evaluated via the specific VISIA algorithms.

Extraction and Physicochemical Characterization of Highly-pure Amorphous Silica Nanoparticles from Locally Available Dunes Sand

This study synthesized highly pure silica nanoparticles from the northeast Algerian Sahara dunes sand as a low-cost silica source using a simple and environmentally friendly method. The silica nanoparticles were extracted using a sodium silicate solution as a precursor without employing any additive agents. The extracted silica’s crystalline structure, chemical composition, chemical bonding, microstructure, elemental analysis, thermal analysis, and optical characteristics were investigated. The X-ray diffraction patterns demonstrate the amorphous nature of the extracted silica. Furthermore, the X-ray fluorescence spectroscopy (XRF) and energy dispersive X-ray (EDX) results prove the high purity of the extracted silica (99% SiO2). However, the Fourier-transform infrared spectroscopy (FTIR) results corroborate the presence of silanol and siloxane groups. According to the SEM image analysis, the produced silica has an average particle size in the range of nanometers. Thermal analysis (TGA/DTA) exhibited the high thermal stability of the silica, and the optical band gap energy for silica nanoparticles was determined to be 3.75 eV. Therefore, dunes sand is an alternative source for developing high-purity silica nanoparticles, which have great potential for advanced material applications.

Discovering small-molecule senolytics with deep neural networks.

The accumulation of senescent cells is associated with aging, inflammation and cellular dysfunction. Senolytic drugs can alleviate age-related comorbidities by selectively killing senescent cells. Here we screened 2,352 compounds for senolytic activity in a model of etoposide-induced senescence and trained graph neural networks to predict the senolytic activities of >800,000 molecules. Our approach enriched for structurally diverse compounds with senolytic activity; of these, three drug-like compounds selectively target senescent cells across different senescence models, with more favorable medicinal chemistry properties than, and selectivity comparable to, those of a known senolytic, ABT-737. Molecular docking simulations of compound binding to several senolytic protein targets, combined with time-resolved fluorescence energy transfer experiments, indicate that these compounds act in part by inhibiting Bcl-2, a regulator of cellular apoptosis. We tested one compound, BRD-K56819078, in aged mice and found that it significantly decreased senescent cell burden and mRNA expression of senescence-associated genes in the kidneys. Our findings underscore the promise of leveraging deep learning to discover senotherapeutics.

Development of a hybridization chain reaction-powered lab-on-fiber device for ultrafast point-of-care testing of circulating tuor DNA in whole blood

Circulating tumor DNA (ctDNA) demonstrates great promise in the guidance of prognostication, diagnosis, and surveillance of cancers, which highlights the need for rapid and sensitive point-of-care testing (POCT) technologies. Hybridization chain reaction (HCR)-based optical biosensors provide excellent solutions due to their prominent features. However, the requirement of a sophisticated and expensive optical readout device, relatively long detection time, and heating hold back their scalability and clinical applications. Here, an innovative HCR-powered lab-on-fiber device (HCR-LOFD) was developed for rapid on-site detection of ctDNA with high sensitivity, specificity, and reproducibility. A LOFD with a compact all-fiber optical structure was constructed for the fluorescence detection of the HCR system. Combining HCR, fluorescence energy resonant transfer, and the evanescent wave fluorescence principle, HCR-LOFD achieved the quantitative detection of KRAS G12D, the 12th amino acid from glycine (Gly) mutated aspartate (Asp) and the most common mutation of KARS, in 5 min at room temperature based on end-point detection mode or real-time fluorescence detection mode. This new assay platform was also successfully applied for the direct detection of KRAS G12D in whole blood with simple dilution. The application of HCR-LOFD not only greatly simplifies the complexity of optical readout devices and improves their scalability but also potentially serves as a sample-to-answer solution for the detection of biomarkers in limited medical resource regions.

Optimization of the C2 substituents on the 1,4-bis(arylsulfonamido)naphthalene-N,N′-diacetic acid scaffold for better inhibition of Keap1-Nrf2 protein-protein interaction

Direct inhibition of the protein-protein interaction (PPI) between Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2) reduces the ubiquitination and subsequent degradation of Nrf2, leading to Nrf2 accumulation in the cytosol and the nuclear translocation of Nrf2. Once inside the nucleus, Nrf2 binds to and activates the expression of antioxidant response element (ARE) genes involved in redox homeostasis and detoxification. Herein, we report a series of 1,4-bis(arylsulfonamido)naphthalene-N,N′-diacetic acid analogs with varying C2 substituents to explore the structure-activity relationships at this position of the central naphthalene core. The Keap1-binding activities were first screened with a fluorescence polarization (FP) assay followed by further evaluation of the more potent compounds using a more sensitive time-resolved fluorescence energy transfer (TR-FRET) assay. It was found that compound 24a with C2-phthalimidopropyl group was the most potent in this series showing an IC50 of 2.5 nM in the TR-FRET assay with a Ki value in the subnanomolar range. Our docking study indicated that the C2-phthalimidopropyl group in compound 24a provided an extra hydrogen bonding interaction with the key residue Arg415 that may be responsible for the observed boost in binding affinity. In addition, compounds 12b, 15, and 24a were shown to activate the Nrf2 signaling pathway in NCM460D cells resulting in elevated mRNA levels of GSTM3, HMOX1 and NQO1 by 2.4–11.7 fold at 100 μM as compared to the vehicle control.

An Air- and Moisture-stable Zinc(II) Carbene Dithiolate Dimer Showing Fast Thermally Activated Delayed Fluorescence and Dexter Energy Transfer Catalysis.

A dimeric ZnII carbene complex featuring bridging and chelating benzene-1,2-dithiolate ligands is highly stable towards air and water. The donor-Zn-acceptor structure leads to visible light emission in the solid state, solution and polymer matrices with λmax between 577-657 nm and, for zinc(II) complexes, unusually high radiative rate constants for triplet exciton decay of up to kr =1.5×105 s-1 at room temperature. Variable temperature and DFT/MRCI studies show that a small energy gap between the 1/3 LL/LMCT states of only 79 meV is responsible for efficient thermally activated delayed fluorescence (TADF). Time-resolved luminescence and transient absorption studies confirm the occurrence of long-lived, dominantly ligand-to-ligand charge transfer excited states in solution, allowing for application in Dexter energy transfer photocatalysis.

Early Stage UV-B Induced Molecular Modifications of Human Eye Lens γD-Crystallin.

In the human eye lenses, the crystallin proteins facilitate transparency, light refraction, as well as UV light protection. A deregulated balanced interplay between α-, β-, and γ-crystallin can cause cataract. γD-crystallin (hγD) is involved in the energy dissipation of absorbed UV light by energy transfer between aromatic side chains. Early UV-B induced damage of hγD with molecular resolution is studied by solution NMR and fluorescence spectroscopy. hγD modifications are restricted to Tyr 17 and Tyr 29 in the N-terminal domain, where a local unfolding of the hydrophobic core is observed. None of the tryptophan residues assisting fluorescence energy transfer is modified and hγD is remained soluble over month. Investigating isotope-labeled hγD surrounded by eye lens extracts from cataract patients reveals very week interactions of solvent-exposed side chains in the C-terminal hγD domain and some remaining photoprotective properties of the extracts. Hereditary E107A hγD found in the eye lens core of infants developing cataract shows under the here used conditions a thermodynamic stability comparable to the wild type but an increased sensitivity toward UV-B irradiation.

TR-FRET-Based Immunoassay to Measure Ataxin-2 as a Target Engagement Marker in Spinocerebellar Ataxia Type 2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited neurodegenerative disease, which belongs to the trinucleotide repeat disease group with a CAG repeat expansion in exon 1 of the ATXN2 gene resulting in an ataxin-2 protein with an expanded polyglutamine (polyQ)-stretch. The disease is late manifesting leading to early death. Today, therapeutic interventions to cure the disease or even to decelerate disease progression are not available yet. Furthermore, primary readout parameter for disease progression and therapeutic intervention studies are limited. Thus, there is an urgent need for quantifiable molecular biomarkers such as ataxin-2 becoming even more important due to numerous potential protein-lowering therapeutic intervention strategies. The aim of this study was to establish a sensitive technique to measure the amount of soluble polyQ-expanded ataxin-2 in human biofluids to evaluate ataxin-2 protein levels as prognostic and/or therapeutic biomarker in SCA2. Time-resolved fluorescence energy transfer (TR-FRET) was used to establish a polyQ-expanded ataxin-2-specific immunoassay. Two different ataxin-2 antibodies and two different polyQ-binding antibodies were validated in three different concentrations and tested in cellular and animal tissue as well as in human cell lines, comparing different buffer conditions to evaluate the best assay conditions. We established a TR-FRET-based immunoassay for soluble polyQ-expanded ataxin-2 and validated measurements in human cell lines including iPSC-derived cortical neurons. Additionally, our immunoassay was sensitive enough to monitor small ataxin-2 expression changes by siRNA or starvation treatment. We successfully established the first sensitive ataxin-2 immunoassay to measure specifically soluble polyQ-expanded ataxin-2 in human biomaterials.

Enabling multiperspective single-molecule FRET.

Single-molecule fluorescence studies enable real-time observation of interactions between molecular machines using minuscule amounts of (potentially) precious samples. Experimental repetition is required for optimizations, to test different samples or conditions, and ultimately to perform technical and biological repeats for publication. Here we developed a multiplexed approach that allows us to significantly increase experimental sensitivity, reproducibility, and throughput of single-molecule fluorescence and fluorescence energy transfer imaging. By coupling this approach with nucleic acid barcoding, microfluidic handling systems, and advanced data processing, we aim to automate and simplify multiperspective single-molecule studies to accelerate the emerging field of dynamic structural biology.

Circularly Polarized Fluorescence Energy Transfer for Constructing Multicolor Circularly Polarized Luminescence Films with Controllable Handedness

Utilizing achiral fluorophores to fabricate circularly polarized luminescence (CPL) materials is of significant importance in both fundamental research and practical applications; chirality transfer has become an indispensable process in routine efforts reported so far. However, this may restrict or even become a bottleneck in further advancing CPL materials starting from achiral fluorophores. Inspired by biological light-harvesting architectural systems, we attempt to establish a new strategy, i.e., circularly polarized fluorescence energy transfer (CPF-ET) to explore multicolor CPL films in the absence of chirality transfer. CPL has been successfully realized through both radiative energy transfer and nonradiative energy transfer. The material systems consist of chiral fluorescent helical polyacetylene working as a circularly fluorescence polarized energy donor and achiral fluorophores as an energy acceptor. Achiral acceptors absorb circularly polarized fluorescence energy from the donor and hence emit the corresponding CPL; accordingly, chirality transfer is no longer an indispensable condition, and the sense of the CPL emission of the achiral fluorophores is controlled by the chiral fluorescent polymer. Moreover, multicolor CPL films can be simply prepared by employing varying achiral fluorophores. This work provides a facile and versatile platform for achieving CPL by taking advantage of achiral fluorophores.

Impact of Fluorescent Light Energy on the Quality of Life of Dogs with Dermatologic Disease and Their Owners

Impact of Fluorescent Light Energy on the Quality of Life of Dogs with Dermatologic Disease and Their Owners

Compositional tuning of gas-phase synthesized Pd-Cu nanoparticles.

Bimetallic nanoparticles have gained significant attention in catalysis as potential alternatives to expensive catalysts based on noble metals. In this study, we investigate the compositional tuning of Pd-Cu bimetallic nanoparticles using a physical synthesis method called spark ablation. By utilizing pure and alloyed electrodes in different configurations, we demonstrate the ability to tailor the chemical composition of nanoparticles within the range of approximately 80 : 20 at% to 40 : 60 at% (Pd : Cu), measured using X-ray fluorescence (XRF) and transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDXS). Time-resolved XRF measurements revealed a shift in composition throughout the ablation process, potentially influenced by material transfer between electrodes. Powder X-ray diffraction confirmed the predominantly fcc phase of the nanoparticles while high-resolution TEM and scanning TEM-EDXS confirmed the mixing of Pd and Cu within individual nanoparticles. X-ray photoelectron and absorption spectroscopy were used to analyze the outermost atomic layers of the nanoparticles, which is highly important for catalytic applications. Such comprehensive analyses offer insights into the formation and structure of bimetallic nanoparticles and pave the way for the development of efficient and affordable catalysts for various applications.

Dual-mode up/down-conversion optical thermometry of Pr&lt;sup&gt;3+&lt;/sup&gt;-regulated Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt; phosphors

Photothermal sensing is crucial in developing smart wearable devices. However, designing and synthesizing luminescent materials with suitable multi-wavelength emission and constructing multiple sets of probes in a single material system is a huge challenge for constructing sensitive temperature sensors with a wide temperature range. In this paper, Pr&lt;sup&gt;3+&lt;/sup&gt;, Er&lt;sup&gt;3+&lt;/sup&gt; single-doped and double-doped Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt; phosphors are successfully prepared by high temperature solid phase method, and their structures, morphologies, excitation wavelengths and temperature-dependent fluorescence properties are characterized by XRD, SEM, fluorescence spectrometer and self-made heating device. Firstly, the photoluminescences of the synthesized series of samples are investigated. The results show that comparing with the single-doped Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;: Er&lt;sup&gt;3+&lt;/sup&gt; sample, the up/down-conversion spectra of Pr&lt;sup&gt;3+&lt;/sup&gt;, Er&lt;sup&gt;3+&lt;/sup&gt; co-doped phosphors under 808 nm/380 nm excitation show that the green fluorescence emission of Er&lt;sup&gt;3+&lt;/sup&gt; is enhanced. In addition, under 980 nm excitation, Pr&lt;sup&gt;3+&lt;/sup&gt; can effectively regulate the fluorescence energy level population pathway, so that the electrons are more effectively arranged in the &lt;sup&gt;2&lt;/sup&gt;H&lt;sub&gt;11/2&lt;/sub&gt; and &lt;sup&gt;4&lt;/sup&gt;S&lt;sub&gt;3/2&lt;/sub&gt; energy levels in the excitation process. The red emission is weakened and the green emission is enhanced, which improves the signal resolution of the fluorescent material and has a significant influence on the optical temperature measurement. Secondly, the up-conversion fluorescence property of Er&lt;sup&gt;3+&lt;/sup&gt; under 808 nm/980 nm laser excitation in Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt; and Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Pr&lt;sup&gt;3+&lt;/sup&gt;,Er&lt;sup&gt;3+&lt;/sup&gt; phosphors are investigated. The results show that the red and green fluorescence emissions of Er&lt;sup&gt;3+&lt;/sup&gt; are two-photon processes. Finally, the up/down-conversion dual-mode temperature sensing properties of Er&lt;sup&gt;3+&lt;/sup&gt; in Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt; and Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Pr&lt;sup&gt;3+&lt;/sup&gt;, Er&lt;sup&gt;3+&lt;/sup&gt; phosphors are investigated. It is found that both materials have good optical temperature measurement performances. The Pr&lt;sup&gt;3+&lt;/sup&gt; doping optimizes the dual-mode optical temperature measurement performances of Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt; phosphors derived from the thermal coupling energy level of Er&lt;sup&gt;3+&lt;/sup&gt; ions. In addition, the up/down-conversion fluorescence mechanism of Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt; and Li&lt;sub&gt;0.9&lt;/sub&gt;K&lt;sub&gt;0.1&lt;/sub&gt;NbO&lt;sub&gt;3&lt;/sub&gt;:Er&lt;sup&gt;3+&lt;/sup&gt;, Pr&lt;sup&gt;3+&lt;/sup&gt; phosphors are proposed, and the enhanced green fluorescence by Pr&lt;sup&gt;3+&lt;/sup&gt; co-doping is attributed to the energy transfer from Pr&lt;sup&gt;3+&lt;/sup&gt; ions to Er&lt;sup&gt;3+&lt;/sup&gt; ions, leading to the increase of green fluorescence level population and the decrease of red fluorescence level population of the Er&lt;sup&gt;3+&lt;/sup&gt; ions. This new dual-mode optical temperature measurement material provides a material basis and optical temperature measurement technology for exploring other temperature measurement materials.

Control of Fluorescence of Organic Dyes in the Solid-State by Supramolecular Interactions.

Fluorescent organic dyes play an essential role in the creation of new "smart" materials. Fragments and functional groups capable of free rotation around single bonds can significantly change the fluorescent organic dye's electronic structure under analyte effects, phase state transitions, or changes in temperature, pressure, and media polarity. Dependencies between steric and electronic structures become highly important in transition from a solution to a solid-state. Such transitions are accompanied by a significant increase in the dye molecular structure's rigidity due to supramolecular associates' formation such as H-bonding, π···π and dipole-dipole interactions. Among those supramolecular effects, H-bonding interactions, first of all, lead to significant molecular packing changes between loose or rigid structures, thus affecting the fluorescent dye's electronic states' energy and configuration, its fluorescent signal's position and intensity. All the functional groups and heteroatoms that are met in the organic dyes seem to be involved in the control of fluorescence via H-bonding: C-H···N, C-H···π, S = O···H-C, P = O···H, C-H···O, NH···N, C - H···C, C - H···Se, N-H···O, C - H···F, C-F···H. Effects of molecular packing of fluorescent organic dyes are successfully used in developing mechano-, piezo-, thermo- fluorochromes materials for their applications in the optical recording of information, sensors, security items, memory elements, organic light-emitting diodes (OLEDs) technologies.

Fluorescent "turn-on" aptamer sensor for sensitive and reliable detection of Golgi glycoprotein 73 based on nitrogen-doped graphene quantum dots and molybdenum disulfide nanosheets

The sensitivity and specificity of Golgi glycoprotein 73 (GP73) are very important for early diagnosis of hepatocellular carcinoma. Herein, we constructed a new-fashioned fluorescent aptamer sensor for GP73 determination based on nitrogen-doped graphene quantum dots (N-GQDS) and molybdenum disulfide (MoS2) nanosheets. N-GQDs with high fluorescence intensity and good stability were screened out, and GP73 aptamer (GP73Apt) is labeled with N-GQDs to form the N-GQDs-GP73Apt fluorescence probe. MoS2 nanosheets can quench the fluorescence of N-GQDs-GP73Apt owing to fluorescence resonance energy transfer mechanisms. After introducing GP73 into the biosensing system, the N-GQDs-GP73Apt specifically bound with GP73 to form the deployable structures, making N-GQDs-GP73Apt far away from MoS2, blocking the fluorescence energy transfer process, and restoring the fluorescence of N-GQDs-GP73Apt. When the GP73 concentration was in the extent of 2.5 ng/mL∼100 ng/mL, the relative fluorescence recovery is linearly relevant to the concentration of GP73, and the limit of detection (LOD) was 1.29 ng/mL (S/N = 3). Moreover in the application of actual serum sample detection, the recovery was range 98.85∼100.55 %. The fluorescent aptamer sensor can rapidly detect and analyze the serum marker GP73 with the characteristics of low-cost, high sensitivity, good specificity and recovery.

Primary radiation damage in bone evolves via collagen destruction by photoelectrons and secondary emission self-absorption

X-rays are invaluable for imaging and sterilization of bones, yet the resulting ionization and primary radiation damage mechanisms are poorly understood. Here we monitor in-situ collagen backbone degradation in dry bones using second-harmonic-generation and X-ray diffraction. Collagen breaks down by cascades of photon-electron excitations, enhanced by the presence of mineral nanoparticles. We observe protein disintegration with increasing exposure, detected as residual strain relaxation in pre-stressed apatite nanocrystals. Damage rapidly grows from the onset of irradiation, suggesting that there is no minimal ‘safe’ dose that bone collagen can sustain. Ionization of calcium and phosphorous in the nanocrystals yields fluorescence and high energy electrons giving rise to structural damage that spreads beyond regions directly illuminated by the incident radiation. Our findings highlight photoelectrons as major agents of damage to bone collagen with implications to all situations where bones are irradiated by hard X-rays and in particular for small-beam mineralized collagen fiber investigations.

Macroscopic quantum electrodynamics approach to multichromophoric excitation energy transfer. II. Polariton-mediated population dynamics in a dimer system.

In this study, based on the theory developed in Paper I, we explore the combined effects of molecular fluorescence and excitation energy transfer in a minimal model-a pair of single-vibration-mode chromophores coupled to surface plasmon polaritons. For the chromophores with zero Huang-Rhys factors and strong couplings to surface plasmon polaritons, we find that the frequencies of Rabi oscillations (the strengths of strong light-matter couplings) are associated with the initial excitation conditions. On the other hand, for the chromophores weakly coupled to surface plasmon polaritons, our numerical calculations together with analytical analysis elaborate on the conditions for the superradiant and subradiant decay behaviors. Moreover, we show that the modified decay rate constants can be explicitly expressed in terms of generalized spectral densities (or dyadic Green's functions), revealing a relationship between photonic environments and the collective effects such as superradiance and subradiance. For the chromophores with nonzero Huang-Rhys factors and strong coupling to surface plasmon polaritons, the effects of molecular vibrations emerge. We demonstrate that the low-frequency vibrational modes do not affect the excited state population dynamics, while the high-frequency vibrational modes can modify either the period of Rabi oscillation (Franck-Condon Rabi oscillation) or the amplitude of excited state population. Our study shows that the collective effects, including superradiance and subradiance, can be controlled via dielectric environments and initial excitation conditions, providing new insights into polariton chemistry and the design of quantum optical devices.

Micrometer‐Scale Optical Web Made of Spider Dragline Fibers with Optical Gate Operations

AbstractDragline silk fibers produced by spiders are a masterpiece structural protein that is durable even in the wild conditions. Dragline silk fibers are known to have excellent mechanical toughness and flexibility and further possess optical transparency, which are highly promising as textiles, sensors, and optical devices. Here, the authors show that the dragline silk microfibers act as good optical waveguides with the optical loss coefficient as small as 0.03 decibel per micrometer. The light transportation in the dragline silk fiber is performed by fluorescence energy transfer between two microspheres located on a suspended dragline silk microfiber. By utilizing a micromanipulation equipment, micrometer‐scale spider web‐like structures are fabricated. The experimentally observed optical waveguiding properties of the weaves match well with simulation results using simple mathematical models. Furthermore, optical logic gate operations are demonstrated using photoswitchable microsphere resonators attached on the dragline fibers.