mCerulean3-Based Cameleon Sensor to Explore Mitochondrial Ca2+ Dynamics In Vivo

Genetically Encoded Ca2+ Indicators (GECIs) are extensively used to study organelle Ca2+ homeostasis, although some available probes are still plagued by a number of problems, e.g., low fluorescence intensity, partial mistargeting, and pH sensitivity. Furthermore, in the most commonly used mitochondrial F\uf6rster Resonance Energy Transfer based-GECIs, the donor protein ECFP is characterized by a double exponential lifetime that complicates the fluorescence lifetime analysis. We have modified the cytosolic and mitochondria-targeted Cameleon GECIs by (1) substituting the donor ECFP with mCerulean3, a brighter and more stable fluorescent protein with a single exponential lifetime; (2) extensively modifying the constructs to improve targeting efficiency and fluorescence changes caused by Ca2+ binding; and (3) inserting the cDNAs into adeno-associated viral vectors for in vivo expression. The probes have been thoroughly characterized in situ by fluorescence microscopy and Fluorescence Lifetime Imaging Microscopy, and examples of their ex vivo and in vivo applications are described

Holstein-Peirls-Hubbard trimer as a model for quadrupolar two-photon absorbing dyes

The linear and nonlinear optical properties of a Donor-Acceptor-Donor system have been investigated by using a two-electron three-point-site model system. Some basic features of electron correlations are included in the model by means of a bi-electronic density matrix. The polarizabilities and second hyperpolarizabilities have been computed with a modified version of the Collective Electronic Oscillators (CEO) method which allowed us to include the electron-phonon coupling. Both singly-and doubly-excited states are taken into account in the computation of (hyper-) polarizabilities. The effects of electron-phonon coupling on the two-photon absorption and on the third harmonic generation in the infrared region are discussed

Optical-properties of Molecular Conductors - One-dimensional Systems With Twofold-commensurate Charge-density Waves

A model is presented for the optical properties in the near to far infrared of a twofold-commensurate one-dimensional system of noninteracting molecular-ion chains. Each chain may be subject to an arbitrary type of lattice distortion that doubles the periodicity of the regular chain and is composed of a lattice dimerization (LD) and/or an alternating molecular deformation (AMD). The effect of an external potential induced by the presence of nearby chains of closed-shell counterions is also accounted for. The linear coupling of the electrons to an arbitrary number of intramolecular modes and to one longitudinal acoustic phonon branch is treated in the adiabatic linear-response approximation. No direct electron-electron interaction is explicitly included but the limit case of noninteracting spinless fermions in a large-U system can be dealt with in the present scheme. The results of the model can be directly applied to the analysis of the experimental infrared data of many conducting organic radical salts of 2:1 stoichiometry where LD and/or AMD of small amplitude occur and the on-site electron-electron correlation is thought to play a major role. The model fitting of the data can be used to obtain information on the one-electron bandwidth, the individual contributions to the total gap of charge density waves components centered on the bonds and on the sites, the relevance of the counterion potential, and the strength of the electron-phonon and electron-molecular vibration interactions. Some of these potentialities as well as the \u2018\u2018selection rules\u2019\u2019 governing the infrared activity of the intramolecular and intermolecular modes as phase phonons are illustrated by numerical model calculations. Self-consistent relations and practical criteria that allow one to use the minimal number of adjustable parameters in the calculations are also presented

Bridging Energetics and Dynamics of Exciton Trapping in Core\u2013Shell Quantum Dots

The widespread application of quantum dots greatly profits from their broad absorption band. However, the variable nature of excitations within these bands is expected to result in undesired excitation energy dependence of steady state emission properties. We demonstrate the different role played by hot and cold carrier trapping in determining fluorescence quantum yields. Our analysis relates the energetic parameters with the available knowledge on the dynamics of charge trapping. It turns out that detrapping processes play a pivotal role in determining steady state emission properties. We studied excitation dependent photoluminescence quantum yields (PLQY) in different CdSe/CdxZn1–xS (x = 0, 0.5, and 1) quantum dots to identify best performing heterostructures in terms of shell thickness and composition. Our rationalization of the observed behavior is focused on the modulation of trapping and detrapping rates. The combination of experimental results and PLQY kinetics modeling reveals the need to consider hot-carrier trapping, supporting recent dynamics observations. This work provides a deeper insight into the trapping process in quantum dots, relating its energetics and dynamics