Mobility of green fluorescent protein in hydrogel-based drug-delivery systems studied by anisotropy and fluorescence recovery after photobleaching.

Modified hydroxyethyl starch is photo-crosslinked in the presence of a green fluorescent protein (GFP) (mTagGFP) to obtain loaded hydrogels as model for a drug-delivery system. An important factor for the protein release is the crosslinking density since a dense network should lead to hindered diffusion. To obtain information on the rotational and translational diffusion of GFP in the hydrogel, mTagGFP is analyzed by fluorescence anisotropy and fluorescence recovery after photo-bleaching experiments using two-photon excitation. The mTagGFP shows a viscosity-retarded rotational and strongly hindered translational diffusion, depending on the polymer concentration. A comparison of anisotropy studies with mTagGFP-loaded microparticles and hydrogel disks allows the polymer concentration to be determined for the microparticles, which has been previously unknown.