A pump for dispensing a fluid from a reservoir provides a drive system seal within the pump. Such methods involve contacting a patient sample with an excess of a detectable crystal-tagging compound reactive with a plurality of crystal species under conditions that allow the detectable crystal-tagging compound to react with a plurality of crystal species, if present, to form tagged crystal species complexes. Concave portions are internally formed at the surfaces of the protrusion electrodes facing each other, and extensions are formed at the peripheries of the surfaces of the protrusion electrodes.