Flow-through 
assay reaction chamber (6) of cassette has back and forth liquid mixing in 
narrow gap (G) over array of capture agent (S), with net flow advance to waste confinement (19), produced by reversible pumps (3 or 12), operable with rolling diaphragm action with at least limited elastic 
recovery that advance sample or buffer liquids through conditioning paths (4A, 8, 8′, 9, 14, 15, 15′) before reaching the 
reaction chamber (6). A single pump produces accurate flow control, liquid conditioning, e.g., liquefying dry 
reagent from internal surfaces of flow-dividing material (14a, 15A, 15A′, e.g. 
open cell foam or 
frit), heating (4A), and 
air bubble removal (8, 8′, 9), as well as replenishment of 
reagent while accomplishing mixing within the flow-through 
reaction chamber (6). Lower 
viscosity buffer liquid is arranged to propel higher 
viscosity reagent, the flow-dividing 
storage material preserving reagent concentration. A 
blister pack (11) acts as a reversible pump (12) in producing accurate forward and backward flows with the net flow advance. Cascaded bubble traps (8, 9) on the cassette render the 
system tolerant of minor pumping error during cassette priming.