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Microscopy of the Heart || Optogenetic Tools in the Microscopy of Cardiac Excitation-Contraction Coupling
摘要： Microscopy became a scienti?c investigation method in the seventeenth century with the application of the ?rst build microscopes on biological samples [1, 2]. Soon it became a popular method to stain samples in order to visualise particular (cellular and subcellular) structures [3]. These stains, either based on absorption or ?uorescence, have limitations in respect to their speci?city and are often toxic to cells, which limits investigations to short intervals or even dead samples. In 1987 the idea came up to use a ?uorescent protein that was discovered 25 years before [4], in particular a green ?uorescent protein (GFP) form the medusa Aequorea victoria to label cells and cellular structures [5]. With the sequencing and cloning of GFP, a so-called ‘green revolution’ started, which led to regular usage of ?uorescent proteins as markers or sensors (for details see below) in the majority of cellular research in physiology, microbiology, pharmacology, molecular biology, anatomy, cell biology, biophysics and many other biomedical ?elds. Although the expression of the ?uorescent proteins and their optical investigation can already be regarded as optogenetic tools, this term was only applied when the optical properties of proteins were used to manipulate cells. The best-known example of such a protein is the channelrhodopsin, a light-gated ion channel [6, 7]. When this ion channel is expressed in a membrane and illuminated with light of the appropriate wavelength, the channel will be activated and opened, which results in passive transportation of ions across the membrane and a change of the membrane potential. However, within this chapter we consider both aspects, the observation and the manipulation as optogenetic tools. To use the optogenetic tool, the genes of these proteins need to be transferred into the cells to allow the expression of the protein. For an overview of gene delivery into target cells, see [8].
关键词： channelrhodopsins,cardiac excitation-contraction coupling,F?rster Resonance Energy Transfer,genetically encoded biosensors,Optogenetic tools,microscopy
更新于2025-09-04 15:30:14
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Design and energy transfer mechanism for single-phased Gd2MgTiO6: Bi3+, Eu3+ tunable white light-emitting phosphors
摘要： In recent years, numerous efforts have been made to develop single-phased white light-emitting phosphors for the near-UV region to solve problems of color reabsorption and ratio regulation between different phosphors. In this work, we have designed Bi3+- and Eu3+-codoped single-phased Gd2MgTiO6 phosphors to achieve tunable white light emission based on multi-luminescence center energy transfer. The structural analysis showed that all the samples were crystallized as a monoclinic double perovskite with the P21/n symmetry space group (No. 14), with HRTEM images showing clear lattice fringes between the lattice planes. The single Bi3+-doped Gd2MgTiO6 sample exhibits two obvious emission peaks at 417 and 508 nm, which correspond to a characteristic 3P1 → 1S0 transition for the Bi3+ ions under near-UV excitation due to two types of Bi3+ emission centers, with their relative emission intensity depending closely on the value of the excitation wavelength. In this case, a suitable choice of excitation wavelength can achieve tunable emission for Gd2MgTiO6: Bi3+ between blue and green. Eu3+ is codoped into Gd2MgTiO6 as a red emission component and shows sharp emission lines that correspond to the characteristic 5D0 → 7FJ (J = 1, 2, 3, and 4) transitions of Eu3+ ions. Energy transfer in Gd2MgTiO6: Bi3+, Eu3+ has been confirmed by the electric dipole–dipole (d–d) interaction from Bi3+ to Eu3+. Our experiments show that it is straightforward to create tunable white light emission by adjusting the excitation scheme and Eu3+ concentration. Moreover, a schematic for the energy transfer mechanism and simplified spectral levels based on Bi3+ and Eu3+ ions has also been established.
关键词： Eu3+,Bi3+,Gd2MgTiO6,white light-emitting phosphors,energy transfer,tunable emission,near-UV
更新于2025-09-04 15:30:14
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Resonance Energy Transfer in Arbitrary Media: Beyond the Point Dipole Approximation
摘要： In this work, we present a comprehensive theoretical and computational study of donor/acceptor resonance energy transfer (RET) beyond the dipole approximation, in arbitrary inhomogeneous and dispersive media. The theoretical method extends Fo?rster theory for RET between particles (molecules or nanoparticles) to the case where higher multipole transitions in the donor and/or acceptor play a significant role in the energy transfer process. In our new formulation, the energy transfer matrix element is determined by a fully quantum electrodynamic expression, but its evaluation requires only classical electrodynamics calculations. By means of a time domain electrodynamical approach (TED), the matrix element evaluation involves the electric and magnetic fields generated by the donor and evaluated at the position of the acceptor, including fields associated with transition electric dipoles, electric quadrupoles, and magnetic dipoles in the donor, and the acceptor response to the electric and magnetic fields and to the electric field gradient. As an illustration of the benefits of the new formalism, we tested our method with a 512 atom lead sulfide (PbS) quantum dot as the donor/acceptor in vacuum, and with spherical nanoparticles (toy model) possessing designed transition multipoles. This includes an analysis of the effects of interferences between multipoles in the energy transfer rate. The results show important deviations from the conventional Fo?rster dipole theory that are important even in vacuum but that can be amplified by interaction with a plasmonic nanoparticle.
关键词： multipole transitions,resonance energy transfer,plasmonic nanoparticle,quantum electrodynamics,dipole approximation,RET
更新于2025-09-04 15:30:14
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Multi-Color Luminescent m-LaPO <sub/>4</sub> :Ce/Tb Monospheres of High Efficiency via Topotactic Phase Transition and Elucidation of Energy Interaction
摘要： Monoclinic (m-) structured (La0.96?xCe0.04Tbx)PO4 phosphor monospheres (x = 0?0.12) of excellent dispersion and morphology uniformity were calcined (≥600 °C) from their precipitated precursor spheres (～2.0 μm) of a hexagonal (h-) structure for efficient and multicolor luminescence. The h → m phase transition, driven by dehydration, was originally proposed to proceed in a topotactic manner, which involves displacement of the RE-O polyhedra (RE: rare-earth) along the a/b axis and slight expansion of the {010} and {100} interplanar spacings of the hydrated h-phase to form the {120} and {100} planes of the anhydrous m-phase, respectively. Analysis of the energy process involving the optically active Ce3+ and Tb3+ ions found efficient Ce3+ → Tb3+ energy transfer occurring via electric dipole?quadrupole interaction, whose efficiency reached the highest value of ～44.48% at x = 0.10. The Tb3+ codoped phosphors simultaneously displayed the characteristic emissions of Ce3+ (～313 nm) and Tb3+ (～545 nm) upon exciting the Ce3+ ions with 275 nm UV light, with which the emission color was finely tuned from dark blue to green by increasing the Tb3+ content. Fluorescence decay analysis found decreasing and almost constant lifetime values for the Ce3+ and Tb3+ emissions at a higher Tb3+ content, respectively, and the phosphor presented the highest external quantum efficiency of ～84.67% at x = 0.10. The excellent luminescent performance and morphology uniformity may allow the monospheres to find application in lighting and display technologies.
关键词： LaPO4,Ce/Tb,energy transfer,multicolor luminescence,quantum efficiency,Monoclinic
更新于2025-09-04 15:30:14