To determine the amount of encapsulated b-galactosidase or formed by IVTT in liposomes, 10 ll of each liposome suspension was diluted in 90 ll Cell lytic B buffer (Sigma, Saint Louis, MO, USA) to disrupt the liposomes and release the produced protein. A same treatment was done with a blank liposomal formulation and standards to correct for possible interferences of lipid components and Cell lytic B buffer with generated fluorescent signal. Subsequently 100 ll of substrate (FDG, 1 mM) was automatically added to each sample and standard and generated fluorescent signal was measured every 0.5 s over a period of 120 s at 25°C using a fluorescent well-plate reader (FLU-Ostar OPTIMA, BMG-Labtech, Offenburg, Germany). To determine the concentration of encapsulated or expressed bgalactosidase, initial substrate conversion slopes (relative light unit (RLU)/s) were determined and compared to those of standards with known concentrations of b-galactosidase (Amidi et al. 2010) .