Fluorescein isothiocyanate labelled bovine serum albumin (FITC-BSA) as a model protein drug: opportunities and drawbacks.

In the therapy of various diseases, parenterally administered protein drugs are of steadily rising importance. In order to reduce the application frequency, these proteins can be incorporated into drug delivery systems, e.g. biodegradable microparticles from poly(lactic-co-glycolic acid) (PLGA). To evaluate the characteristics of these vehicles, fluorescent labelled proteins like fluorescein isothiocyanate labelled bovine serum albumin (FITC-BSA) may be used as model drugs to allow the visualisation of the protein localisation within the microparticle and the detection of microparticles in cell cultures or tissues. However, the quantification of protein by fluorescence spectroscopy failed. In this study we focused on the mechanism of fluorescence dequenching in a multi-FITC-labelled protein and its impact on a reliable protein determination.