This report describes measurement of retention of electroactive ferricyanide (Fe(CN)(6)(3-)) entrapped within structurally stable photopolymerized vesicles composed of diacetylenic lipid 1-palmitoyl-2-(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (PC8,9PC). Vesicle size, shape, and dispersity were assessed by dynamic laser light scattering and rates of permeation of ferricyanide measured by cyclic voltammetry. Gold disk electrodes modified with 6-mercaptohexanol or 2-mercaptoethanamine (cysteamine) respond with quantitative sensitivity to extravesicular ferricyanide over a concentration range of 10,muM to 0.1 M, are insensitive to entrapped ferricyanide even at high applied oxidative potentials, arid resist fouling by vesicles, vesicle fragments, or vesicle-rupturing surfactant. Quantitative changes in ferricyanide peak current over time enabled straightforward determination of ferricyanide permeation rate constants as a function of pH and temperature. At 25 degreesC, ferricyanide permeability increased frown 1.1 x 10(-12) to 2.5 x 10(-12) cm/s with increasing pH from 6 to 8. At pH 7, ferricyanide permeability temperature dependency was found to fit an Arrhenius rate expression, increasing exponentially from 1.6 x 10(-12) to 5.8 x 10(-11) cm/s with increasing temperature from 25 to 70 degreesC, yielding a calculated energy barrier for permeation of 65 kJ/mol and a half-life for intravesicular ferricyanide loss as high as 2.4 weeks. Greater permeability observed at 15 degreesC relative to 25 degreesC is attributed to membrane defects present in the gel-phase. These results are. consistent with diffusion of Fe(CN)(6)(3-) across intact vesicle walls rather than a pore type mechanism and demonstrate the ability to tune retention of entrapped species by robust polymerized vesicles.