Effect of albumin on the fluorescence quantum yield of porphyrin -based agents for fluorescent diagnostics

Abstract

BackgroundAmong modern methods of tumor diagnosis, fluorescent methods are considered one of the most prospective. Diagnostic agents (DAs) spread throughout the body by the bloodstream, so, the DA molecules are often transported by albumins and can be affected by these proteins. In our study we evaluate the effect of complex formation between bovine serum albumin (BSA) and three fluorescence DA’s (Photolon, Photoditazin and Dimegin) on their fluorescent quantum yields. MethodsElectron absorption spectroscopy and fluorescence spectroscopy were carried out to calculate fluorescence quantum yields of the DAs using Rhodamine 6G as a standard fluorescent dye. ResultsFor all three DA’s dissolved in phosphate buffer with pH 7.5 (close to that of blood) the addition of albumin resulted in bathochromic shift of the Soret band as well as change of amplitudes of absorption bands. Similar changes were observed for fluorescence spectra of all DAs that are connected with complex formation between DA and albumin. The presence of isobestic point suggests that DA can present in the solution only in two states, free and BSA-bound. Chlorine-based DA’s demonstrate about 1.5-times higher fluorescence quantum yield in PBS than Dimegin. Nevertheless, the addition of BSA to the solutions of all DA’s decreases sharply their fluorescence quantum yield to approximately equal values. ConclusionThe complex formation between DA and albumin equalize fluorescence efficacies of all studied DAs, so the results of photodymanic diagnostics using the specific DA will depend on other factors.