A microfluidic device includes a first layer of a porous material with pores having a first average pore size and a liquid-receiving area through which a liquid sample is received into the microfluidic device. A second layer of another porous material, with pores of a second average pore size, is stacked below the first layer and has a channel with a starting end positioned at least in part in an overlapping manner with the liquid-receiving area. The channel has a terminating end extending laterally at a predetermined wicking distance from the starting end. The first average pore size and the second average pore size cause a wicking effect in which at least some of the liquid sample flows along the channel at least a portion of the wicking distance between the starting end and the terminating end.