Study of pH gradient on liposomes trapping efficiencie by spectrophotometry: using neutral red

The purpose of this study was to establish a new experimental, rapid, simple and cost effective approach to study liposomes. NR (Neutral red) was selected as a model of lipophilic and hydrophilic drug. NR is an indicator of pH and a weak base with pka=6.7 which is red while ionized in acidic media but yellow while non-ionized in alkaline media and is used in vital staining. In this study the effects of pH internal (5) and external media (5- 9) on liposomes trapping efficiencies in wavelength of 533nm were examined. %EE is (the entrapment efficiency of liposome) increased between (%24-%87) in pH (external media) range 5-9. CBC (CBC, contrast between liposomal compartment for visualized by LM) and EBC (EBC, exchanged between liposomal compartment) and EE were calculated. Liposomes with the internal (pH = 5) and external media (pH = 9) is the most suitable option for staining with NR. No significant correlations were observed among the two index with a 95% coefficient interval (EBC with CBC, r2 = 0.93, p<0.05, and EE with CBC r2=0.93, p 0.05). Significant correlations were also observed among the EBC index and EE index with a 95% coefficient interval (EBC with EE r2=0.66, p<0.05). NR accumulates in liposomes in ionized form therefore, giving sharp contrast with the surrounding media of liposomes. This makes them to be visualized by LM (light microscope).