A new microcapillary device based on an interdigitated electrode array is presented. Microcapillaries with metal electrodes at their bottom are formed as trenches in SiO2 and are open at the top. In an electrolyte solution, the ac current applied to electrodes flows from one capillary to another and is significantly affected by changes in surface conductance at the SiO2/electrolyte interface. The effect of electrostatically assembled charged polyelectrolyte layers on the surface conductance is studied.