electrodes within the mold so that upon introduction of the polymeric material into the mold the electrodes will be appropriately placed and fixed within the substrate alternatively the electrodes and other elements may be added after the substrate is formed using well known microfabrication methods e g sputtering or controlled vapor deposition methods followed by chemical etching and the like in operation the materials stored in the reservoirs are transported electroosmotically through the channel system delivering appropriate volumes of the various materials to one or more regions on the substrate in order to carry out a desired analysis or synthesis to provide such controlled electroosmotic flow the microfluidic system includes a voltage controller electrically connected to electrodes placed or fabricated into the various reagent wells on the device the voltage controller is capable of applying selectable voltage levels to each of the ports or reservoirs including ground such a voltage controller can be implemented using multiple voltage dividers and multiple relays to obtain the selectable voltage levels desired typically the voltage controller is interfaced with a computer or other processor e g a pc compatible pentium microprocessor based or macintosh power pc computer which is programmed to instruct appropriate application of voltages to the various electrodes in operation fluid transport within these devices is carried out by applying a voltage gradient along the path of desired fluid flow thereby electroosmotically driving fluid flow along that path some methods for affecting electroosmotic fluid flow incorporate a u201c floating port u201d fluid direction system where a sample fluid in one reservoir and channel is drawn across the intersection of that channel with another channel by applying a voltage.