Formation, structure and wettability of fluorescent nanolayers of oligoperoxide europium complexes adsorbed to glass surface

Formation kinetics and the nanolayer structure are determined for fluorescent complexes, which are composed of oligoperoxide and europium (OP-Eu), and are adsorbed to glass from water-ammonia solutions. The effective surface fraction x modified by OP-Eu is evaluated (with the Cassie equation) from receding contact angles. Its temporal behavior is repeated by the average adlayer thickness d, determined from ellipsometry, indicating rapid adsorption followed by gradual desorption. The fraction x increases with d to saturate at ∼ 90% for 57 nm. Atomic Force Microscopy micrographs and refractive indices do not reflect simple composite surfaces. Therefore a thickness effect on OP-Eu surface energy is also advocated. Fluorescent microscopy confirms luminescent properties of OP-Eu, applicable for protein detection.     

Near-field microscopy of collapsed Langmuir–Blodgett films

Fluorescence near-field scanning optical microscopy (FL-NSOM) is used to probe the nanoscale structure in stained phospholipid monolayers deposited on glass substrates at moderate surface pressures. The FL-NSOM images reveal new liquid-expanded (LE) and liquid-condensed (LC) domains, including one-to-one correlation between fluorescence contrast and film topography. In particular, films of the phospholipid DPPC stained with DiIC₁₂ exhibit multilayer structures that are observed within the solid phase domains and have LE-like fluorescence signals. These features are attributed to clusters of dye molecules resulting from the localized collapse of the film upon compression. Such collapsed features are also observed in supported films of 100% DiIC₁₂ deposited at high surface pressure. In these films, spatially-resolved spectroscopy shows that the collapsed structures are amorphous based on the fluorescence spectrum while the molecules within the solid phase of the film have a fluorescence spectrum indicative of molecular aggregates.     

EEM fluorescence spectroscopy as a fast method to assess the brine composition of salted herring

Ripening of barrel-salted herring (Clupea harengus) is evaluated by the use of fluorescence spectroscopy and protein determinations. During ripening, protein degradation takes place in the herring and protein is extracted into the brine. The present study aims at identifying parameters which are correlated to the ripening characteristics of barrel-salted herring and which can provide a better understanding of the ripening process. Front face fluorescence landscapes were obtained by measuring directly on the brine from barrel-salted herring. These data were analyzed by parallel factor analysis (PARAFAC), which revealed four fluorophores, tryptophan (two states), vitamin B6 and riboflavin. All four parameters showed an increase in concentration during the storage period corresponding to an increase in protein content that varied from 3 g/100 g at day 60 to 5 g/100 g after 277 days of storage. It was not possible to see a difference in the development of the four fluorophores during the ripening period. The protein content was predicted from the fluorescence landscapes by partial least squares (PLS). The use of unfolded fluorescence spectra gave an RMSECV of 0.26 g/100 g and a correlation between the measured protein content and the predicted values of 0.86.     

Concentration effects on Pr luminescence in LaAlO3 crystals

Concentration dependant emission spectra and fluorescence dynamic profiles have been investigated in Pr_xLa_1−xAlO₃ single crystals in order to better understand processes responsible for concentration quenching of the praseodymium ³P₀ and ¹D₂ emissions. The cross-relaxation transfer rates were experimentally determined as a function of Pr³⁺ concentration. Decays were modeled and nearest-neighbor trapping rates were calculated.     

A benzothiazole-based semisquarylium dye suitable for highly selective Hg sensing in aqueous media

A novel semisquarylium dye was synthesized by the reaction between 3,4-dibutoxy-3-cyclobutene-1,2-dione and a benzothiazolium salt and its metal ion sensing properties were investigated using absorption and emission spectroscopy. These misquarylium exhibited high selectivity for Hg²⁺ ions, as compared with Ca²⁺, Pb²⁺, Al³⁺, Ce²⁺, Ba²⁺, Ni²⁺, Cd²⁺, Zn²⁺ and Mg²⁺ ions in DMSO/H₂O (9:1, v/v), which was attributed to the formation of a 2:1 BSQ:Hg²⁺ coordination complex, the formation of which was supported by the calculated geometry of the complex.     

New optical material europium EDTA complex in polyvinyl pyrrolidone films with fluorescence enhanced by silver plasmons

In our search for efficient Luminescent Solar Concentrators (LSC) we have prepared polyvinyl pyrrolidone (PVP) films incorporated by ethylenediamine tetraacetic acid (EDTA) complex of europium and co-doped with silver nanoparticles (NPs). Steady state fluorescence was studied under weak and strong excitation. Dynamical study was performed by second harmonic of Nd laser. Under weak excitation the fluorescence of europium co-doped with silver plasmons increased by a factor of three and excited by continuous laser by a factor of 50. The lifetimes of films doped by the complex were 755 μs and co-doped with silver nanoparticles 946 μs. This is the first finding that the photon density accumulates the number of plasmons interacting with electronic states of europium increasing its transition probability resulting in the strong intensification of fluorescence. In dynamical measurements of lifetimes a single pulse does not provide enough energy to create such number of plasmons.     

Cover Picture: Preparation and Application of Novel Microspheres Possessing Autofluorescent Properties (Adv. Funct. Mater. 16/2007)

On p. 3153, Guang‐Hui Ma and co‐workers report on the development of autofluorescent chitosan microspheres with tunable color based on different crosslinking reagents and further chemical modification. The fluorescent intensity can also be controlled by the particle size and crosslinking degree. The autofluorescent microspheres may be useful in fluorescence assays as bright, inexpensive, and stable probes for qualitative and quantitative studies of biological interactions and drug delivery. Fluorescent microspheres are widely used as biological tracers. In this study, uniformly sized chitosan microspheres crosslinked with glutaraldehyde (CG microspheres) and formaldehyde (CF microspheres) are successfully prepared by the Shirasu Porous Glass (SPG) membrane emulsification technique. Selectively reduced CG microspheres (SRCG microspheres) are obtained by NaBH₄ reduction. These chitosan microspheres are found to exhibit fluorescent properties without conjugation to any fluorescent agent. The fluorescence color varies with different crosslinkers and can be modulated by further chemical reduction, whereas the fluorescence intensity can be controlled by tuning the particle size and degree of crosslinking. The autofluorescence of the microspheres is applied to study the phagocytosis of HepG2 cells using the microspheres as novel tracers. Quantitative and qualitative evaluations show that these chitosan microspheres serve as bright, inert, durable, and extremely photostable tracers.     

An FFT-based method for attenuation correction in fluorescence confocal microscopy

A problem in three-dimensional imaging using a confocal scanning laser microscope (CSLM) in the (epi)fluorescence mode is the darkening of the deeper layers due to absorption and scattering of both the excitation and the fluorescence light. A new method is proposed to correct for these effects. The approach, valid for weak attenuation, consists of multiplying the measured fluorescence intensity by a correction factor involving a convolution integral of the measured signal, which can be computed efficiently by the fast Fourier transform. Analytical and numerical estimates are given for the degree of attenuation under which the method is valid, and the method is applied to various test images. A real CSLM image is restored. Finally, the method is compared with a recent iterative method with regard to numerical accuracy and computational efficiency.     

丙酮酸荧光分光光度法在黄原胶质量控制上的应用

对影响丙酮酸荧光的各种因素进行了研究,最后得到利用丙酮酸荧光强度控制黄原胶质量的最佳条件,即30%的乙醇溶液,其中Ba2+为0.04mol/L时,pH值为1.71。在激发波长为233nm、发射波长为343nm处测黄原胶水解产物的荧光强度,可有效地控制黄原胶的质量。