Abstract: A cartridge for analyzing a biological fluid, comprises an array of channels defining a plurality of analysis paths. Each channel is defined by at least two channel walls facing each other and defining a channel height. A wall of at least one channel has a step for defining on either side of the step: —a first segment of the channel wherein the wall has a first surface energy and a first elevation defining a first height of the channel; —a second segment of the channel wherein the wall has a second surface energy and a second elevation defining a second height of the channel. The first height of the channel and the first surface energy of the wall are greater than the second height of the channel and the second surface energy, respectively.