Photophysics of DFHBI bound to RNA aptamer Baby Spinach

The discovery of the GFP-type dye DFHBI that becomes fluorescent upon binding to an RNA aptamer, termed Spinach, led to the development of a variety of fluorogenic RNA systems that enable genetic encoding of living cells. In view of increasing interest in small RNA aptamers and the scarcity of their photophysical characterisation, this paper is a model study on Baby Spinach, a truncated Spinach aptamer with half its sequence. Fluorescence and fluorescence excitation spectra of DFHBI complexes of Spinach and Baby Spinach are known to be similar. Surprisingly, a significant divergence between absorption and fluorescence excitation spectra of the DFHBI/RNA complex was observed on conditions of saturation at large excess of RNA over DFHBI. Since absorption spectra were not reported for any Spinach-type aptamer, this effect is new. Quantitative modelling of the absorption spectrum based on competing dark and fluorescent binding sites could explain it. However, following reasoning of fluorescence lifetimes of bound DFHBI, femtosecond-fluorescence lifetime profiles would be more supportive of the notion that the abnormal absorption spectrum is largely caused by trans-isomers formed within the cis-bound DFHBI/RNA complex. Independent of the origin, the unexpected discrepancy between absorption and fluorescence excitation spectra allows for easily accessed screening and insight into the efficiency of a fluorogenic dye/RNA system.

Preparation and photoluminescence study of Alumin o-boro silicate YAG fluorescent glass for White LED

The YAG: Eu 3+ fluorescent glass for NUV(near ultraviolet) white LEDs was obtained firstly by synthesizing Y 3 Al 5 O 12 (YAG): Eu 3+ precursors through a simple co-precipitation method, and then mixing precursor with B 2 O 3 -Al 2 O 3 -SiO 2 -Na 2 O-BaO glass powder calcined at 1400°C for 2.5 hours. The as-prepared YAG glass-ceramic phosphor was investigated by DTA, XRD, SEM, and photoluminescence (PL). Influence of YAG: Eu 3+ precursor and Eu 3+ doping on excitation and emission spectra also have been studied. The results show that: the phosphor's emission peak located at 393nm is correspond to the 7 F 0 - 5 L 6 transition of Eu 3+ ions, which matches good with UV LED chips; the phosphor gives intense emission at 593nm originating from the 5 D 0 - 7 F 1 transition of Eu 3+ ions. When the YAG precursor is 0.9g and amount of Eu 3+ doped is 0.08, the fluorescence excitation spectra of glass and emission spectra of the peak intensity reach its maximum value. The YAG: Eu 3+ fluorescence glass could be a promising material for the production of near ultraviolet chip white light-emitting diode.

Asymmetry in the Qy Fluorescence and Absorption Spectra of Chlorophyll a Pertaining to Exciton Dynamics

Significant asymmetry found between the high-resolution Qy emission and absorption spectra of chlorophyll-a is herein explained, providing basic information needed to understand photosynthetic exciton transport and photochemical reactions. The Qy spectral asymmetry in chlorophyll has previously been masked by interference in absorption from the nearby Qx transition, but this effect has recently been removed using extensive quantum spectral simulations or else by analytical inversion of absorption and magnetic circular dichroism data, allowing high-resolution absorption information to be accurately determined from fluorescence-excitation spectra. To compliment this, here, we measure and thoroughly analyze the high-resolution differential fluorescence line narrowing spectra of chlorophyll-a in trimethylamine and in 1-propanol. The results show that vibrational frequencies often change little between absorption and emission, yet large changes in line intensities are found, this effect also being strongly solvent dependent. Among other effects, the analysis in terms of four basic patterns of Duschinsky-rotation matrix elements, obtained using CAM-B3LYP calculations, predicts that a chlorophyll-a molecule excited into a specific vibrational level, may, without phase loss or energy relaxation, reemit the light over a spectral bandwidth exceeding 1,000 cm−1 (0.13 eV) to influence exciton-transport dynamics.

Plasmon enhancement of fluorescence of phthalocyanines metallocomplexes in solutions of silver nanoparticles

A method of creation of aqueous solutions with silver nanoparticles for studying of fluorescence of hydrophobic compounds has been proposed for metallocomplexes of phthalocyanines. The effect of silver nanoparticles on the fluorescence of phthalocyanines metallocomplexes at room and low temperatures was studied. The addition of silver nanoparticles leads to plasmonic enhancement of signals in fluorescence and fluorescence excitation spectra of the compounds of interest from 1,5 to more than 7 times. The lifetimes and quantum yield of fluorescence were measured for solutions of metallophthalocyanines in binary mixtures and in binary mixtures with the addition of silver triangular nanoplates with shells of silicon dioxide.

Single-Cell and Bulk Fluorescence Excitation Signatures of Seven Phytoplankton Species During Nitrogen Depletion and Resupply

Phytoplankton play a vital role as primary producers in aquatic ecosystems. One common approach to classifying phytoplankton is fluorescence excitation spectroscopy, which leverages the variation in types and concentrations of pigments among different phytoplankton taxonomic groups. Here, we used a fluorescence imaging photometer to measure excitation ratios (“signatures”) of single cells and bulk cultures of seven differently pigmented phytoplankton species as they progressed from nitrogen N-replete to N-depleted conditions. Our objective was to determine whether N depletion alters the fluorescence excitation signature of each species and, if so, how quickly they recover when N (as nitrate) was resupplied, because these factors affect our ability to classify the species correctly. Of the seven species studied, only Proteomonas sulcata, a marine cryptophyte, showed measurable changes in single-cell fluorescence excitation ratios and bulk fluorescence excitation spectra. These changes were likely due to decreases in the cellular concentration of phycoerythrin, a N-rich pigment, as N became scarce. Within 3 h of resupply of N, fluorescence signatures began returning to pre-depletion values and were indistinguishable from N-replete cells by 80 h after resupply. These data suggest that our classification approach is robust for non-PE containing phytoplankton. PE-containing phytoplankton might exhibit systematic changes in their signatures depending on their level of N depletion, but this could be detected and the phytoplankton re-classified following a few hours of incubation in N replete conditions.

Structural and time-domain peculiarities of the fluorescence excitation spectra of single Mg-TAP in a polymer at low temperatures

The results of low-temperature measurements of spectral trails (temporal evolutions of individual fluorescence excitation spectra) of single molecules Mg-tetraazaporphyrin embedded in polyisobutylene are presented. Spectral trails were recorded in a broad spectral range (up to 4000 GHz) at a temperature 6K. Spectral diffusion in a broad spectral range has been found. Individual spectra of single molecules with a broad peak shifted with respect to zero-phonon line at ~14 – 15 cm-1 were recorded. These broad peaks can be interpreted as the phonon sidebands.