The primary method for neuronal communication involves the extracellular release of small molecules that are packaged in secretory vesicles. We have developed a platform to separate, lyse, and electrochemically measure the contents of single vesicles using a hybrid capillary-microfluidic device. This device incorporates a sheath-flow design at the outlet of the capillary for chemical lysis of vesicles and subsequent electrochemical detection. The effect of sheath-flow on analyte dispersion was characterized using confocal fluorescence microscopy and electrochemical detection. At increased flow rates, dispersion was minimized, leading to higher separation efficiencies but lower detected amounts. Large unilamellar vesicles (diameter approximately 200 nm), a model for secretory vesicles, were prepared by extrusion and loaded with an electroactive molecule. They were then separated and detected using the hybrid capillary-microfluidic device. Determination of size from internalized analyte concentration provides a method to characterize the liposomal suspension. These results were compared to an orthogonal size measurement using dynamic light scattering to validate the detection platform.