Photophysical, rotational and translational properties of Radachlorin photosensitizer upon binding to serum albumins.

INTRODUCTION: Although photophysical properties of Radachlorin photosensitizer (PS) were extensively studied in solutions and cells, no data is available on variations of its characteristics upon binding to serum albumins, which are major transporters in blood and nutrients in cell culture media. OBJECTIVES: The primary objective of this study was to analyze changes in photophysical properties of Radachlorin molecules upon their binding to human and bovine serum albumins at different microenvironment properties. METHODS: Experiments were performed using time-resolved fluorescence spectroscopy and fluorescence recovery after photobleaching. Variations in fluorescence spectra and lifetime, fluorescence anisotropy, rotational and translational diffusion of PS molecules upon binding to albumins were studied in normal, basic and acidic conditions and at different concentrations of albumin and PS molecules. RESULTS: Radachlorin molecules effectively bind to both types of serum albumins, which causes changes in photophysical properties of the PS. A minor red shift of the fluorescence spectrum, an increase in fluorescence lifetime and anisotropy and substantial decrease of translational and rotational mobility of PS molecules were observed upon their binding to albumins. The analysis of rotational diffusion time provided robust evaluation of the bound fraction of PS molecules. Both the highly acidic microenvironment and increase in alcohol concentration above 40% resulted in detachment of PS molecules from albumins. Photophysical properties of Radachlorin in complexes with BSA and HSA were found to be slightly different. CONCLUSIONS: Binding of Radachlorin photosensitizer to either BSA or HSA affects significantly its photophysical properties, which may also vary with microenvironment acidity and alcohol concentration.

Fluorescence anisotropy in indole under two-photon excitation in the spectral range 385-510 nm.

This paper presents the detailed study of two-photon excited fluorescence in indole dissolved in propylene glycol produced by two-photon absorption from the molecular ground state to several high lying excited states. The experimental method involved excitation with linearly and circularly polarized femtosecond pulses and time-resolved detection of the polarized fluorescence decay. The fluorescence intensity, anisotropy, excited state lifetime, and rotation diffusion time as function of the excitation light wavelength in the spectral range 385-510 nm were determined in experiment. The theoretical fit of the experimental results obtained demonstrated the contributions of six highly excited molecular states of different symmetry to the two-photon absorption intensity and fluorescence anisotropy. An intense two-photon absorption peak was observed experimentally in the spectral range 385-480 nm and explained as contributions from four high lying electronic excited states. The temporal dependence of fluorescence intensity in indole was satisfactory characterized by a single excited state lifetime τf and a single rotational diffusion time τrot. As shown, the excited state lifetime τf depends on the excitation light wavelength, which was explained by taking into account nonradiative relaxation transitions in the molecular vibronic excited states. The rotation diffusion time τrot was found to be equal to τrot = 0.9 ± 0.5 ns and practically independent of the excitation wavelength. The determined molecular anisotropy changed substantially in the spectral area 385-480 nm taking positive and negative values, and the anisotropies referring to linearly and circularly polarized excitation light changed almost in opposite phases with each other. The experimental results obtained were interpreted using ab initio molecular structure computations and a model based on the Frank-Condon approximation and taking into account vibronic absorption bands.

Enhancement of spontaneous emission in Tamm plasmon structures.

It was theoretically and experimentally demonstrated that in metal/semiconductor Tamm plasmon structures the probability of spontaneous emission can be increased despite losses in metal, and theoretical analysis of experimental results suggested that the enhancement could be as high as one order of magnitude. Tamm plasmon structure with quantum dots has been fabricated and the emission pattern has been measured. Electromagnetic modes of the structure have been analyzed and modification of spontaneous emission rates has been calculated showing a good agreement with experimentally observed emission pattern.