Abstract: A backing sheet (101) is provided with a pattern of pathways (131,132,133) of (e.g.) silica or cellulose by a printing process (e.g., screen printing). There may be multiple pathways leading from an eluant application region (117) to a detection zone (116) and thence to a waste reservoir (118). Different pathways may have different fluid traversal times because they differ in length and/or material (e.g., nitrocellulose for slow traversal and fibrous cellulose for rapid traversal by an aqueous liquid). Thus analyte and reagents deposited at depots (112,113) on different pathways are sequentially delivered to the detection zone. Reagents may be applied by printing. The detection zone may have an electrode assembly (105), also applied by printing, for detecting the effects of analyte.