Encapsulation and Releasing of Calcein by Spontaneously Formed Zwitterionic/Anionic Vesicle without Separation

The encapsulation and releasing of fluorescence dye calcein by spontaneously formed vesicle, from the mixtures of anionic surfactant (sodium dodecyl benzene sulfonate) and zwitterionic surfactant (Lauryl sulfonate betaine), was characterized with a simple but sensitive and accurate fluorescence method, using cobalt chloride as a quenching agent. Different from the separation method, the whole process proceeded in the same solution without removing the free calcein. After cobalt chloride quenching the outer calcein, the releasing of the calcein from the vesicle to bulk solution starts and finally reaches a steady value depending on the equilibrium between the osmotic pressure and resistance of membrane. The entrapment quantity of the SDBS/LSB vesicles to the calcein could then be deduced according to the difference of fluorescence intensity before and after the quenching, which varies with the mixing ratios of the two kinds of surfactants. The addition of additives such as salt and especially the polymer (polyvinylpyrrolidone) reduces the releasing velocity by strengthening the bilayers, and increases the encapsulation quantity, even 3times at the most.