ends act as ports to introduce the contents of the reservoirs 42 and 44 into the microchannel structure 22 each reservoir 42 and 44 is similar in construction to the other reservoirs with the ends of the second transverse portion being in fluid communication with the bottom of each respective reservoir 42 and 44 one or more types of single stranded dna probes 46 are attached at individual sites within the microchannel portion 24 of the microchannel structure 22 the design and fabrication of microchips and the electrokinetic transport of fluids through the microchannels is described in u s ser no 08 283 769 filed aug 1 1994 hereby incorporated by reference the microchips described therein include planar glass substrates into which the microchannels are etched photolithographically the reservoirs typically hold analyte solutions buffers reagents etc typical microchannel dimensions are 10 u03bcm by 50 u03bcm depth u00d7 width although channel widths of 1 u03bcm to gt 100 u03bcm and channel depths of lt 1 u03bcm to gt 100 u03bcm may be used voltages are applied to solutions as described in the aforementioned application to produce electroosmotic flow of fluids or electrophoretic migration of charged species through the channels alternatively pressure or vacuum may be applied to one or more fluid reservoirs to cause reagent flow through the channels the individual dna probes may be arranged in a linear pattern as shown in fig2 an alternative embodiment is shown.