ABSTRACT
The spectral behavior of calcein, a water-soluble self quenching fluorescent marker often used in biomedical analysis, can be considerably affected by the presence of surfactants. With this study we intend to obtain further information on the photophysical properties of calcein, in the presence of surfactants and in the concentration range commonly used to investigate the release of such marker from vesicle dispersions. The experiments were carried out both in water and in a physiological buffer (HEPES, pH 7.5), in the presence of Triton X-100, sodium dodecyl sulphate and centyltrimethylammonium bromide, both below and above their critical micelle concentration (c.m.c.). The obtained results confirm that calcein fluorescence can be affected by the presence of surfactants. Thus, environmental conditions must always be carefully checked for the actual quantitative evaluation of this dye. Furthermore, this study sheds some light on the nature and mechanism of calcein quenching.
Subject(s)
Cetrimonium Compounds/chemistry , Detergents/chemistry , Fluoresceins/analysis , Octoxynol/chemistry , Sodium Dodecyl Sulfate/chemistry , Cetrimonium , Evaluation Studies as Topic , Fluoresceins/chemistry , Fluoresceins/metabolism , Fluorescence , HEPES/chemistry , Micelles , Octoxynol/metabolism , Spectrometry, FluorescenceABSTRACT
Large phosphatydilcholine unilamellar vesicles appear to be suitable controlled and protective delivery systems of beta-galactosidase. Kinetic measurements carried out on intact loaded liposomes show that most of the enzyme is entrapped inside the liposomes and its activity is latent. Nevertheless, intact liposomes also show significant activity, which can be controlled by addition of detergent. At sublytic detergent concentrations, liposome enzymatic activity reaches values two or three times greater than those of intact liposomes. This increase seems to be due to membrane structure modification that also enhances the substrate permeability across the bilayer. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 261-266, 1997.
ABSTRACT
The spectral behaviour of calcein, a water-soluble self-quenching molecule that is often used as a marker in biomedical analysis, can be considerably affected by the presence of surfactants. The aim of this work was to investigate the spectral properties of calcein under conditions that are particularly significant in liposome studies. For this purpose the fluorescence and absorbance of this dye were determined in solutions of ionic and non-ionic surfactants (cetyltrimethylammonium bromide, sodium dodecyl sulphate and Triton X-100), at different concentrations below and above their critical micelle concentrations (c.m.c.) as well as in the presence of phospholipids in the form of liposomes and/or mixed micelles. Cationic surfactants induced changes in lambda max, absorbance and fluorescence but these changes were less noticeable in the phospholipid dispersions. The anionic and the non-ionic surfactants induced mainly changes in fluorescence intensity.
