An electrode assembly (1) for resistive pulse spectroscopy comprises two flat electrodes (3) substantially equal in size and shape and supported in face-to-face, parallel relationship ot one another, and a plate-like fluid-tight insulator (2) positioned between the electrodes and extended beyond the periphery of the electrodes with the electrodes (3) being fixed to the insulator (2). Each electrode has a hole (4) extending through the electrode in a central region thereof (4), the holes (4) of the two electrodes (3) being aligned with one another. The insulator (2) has a cavity (5) which receives an initially separate element (40) having a preformed aperture (16) therein which is located substantially centrally with respect to the holes (4) in the electrodes (3) and has a smaller diameter than the said holes, the aperture (16) being located such as to allow a flow of liquid to pass therethrough and through the holes in the electrode.
