Fluorescence correlation spectroscopy for the characterisation of drug delivery systems

Fluorescence Correlation Spectroscopy (FCS) offers the possibility to measu re molecular interactions between active compounds and drug delivery system s such as cationic peptides or polymeric nanoparticles. In order to investi gate the potential of FCS for drug carrier design, a complex made of protam ine, a cationic peptide, and a 19mer oligonucleotide was characterised, Pro tamine was used to form proticles, agglomerates consisting of the oligonucl eotide and the cationic peptide. The binding kinetics and proticle formatio n was studied by FCS. Complete binding of the oligonucleotide to protamine was achieved at a 1:2.5 (w/w) ratio. From the diffusion coefficient, D, a m ean value for the hydrodynamic diameter was calculated at 53 nm, which was in agreement with data obtained from photon correlation spectroscopy (PCS). Oligonucleotide loading into cationic monomethylaminoethylmefhacryrate (MM AEMA) nanoparticles was also determined by this method at 5.6 % (5.6 mug pe r 100 mug of nanoparticles).