Microfluidic ratchets to separate leukocytes directly from whole blood. (A) Image of the sorting region of microfluidic ratchets infused with food color dyes illustrating the diagonal trajectory of the sample inlet flow. (B–E) Images of the leukocytes stained with Hoechst 33342 being separated from the whole blood and traversing diagonally through the funnel matrix. (F,G) Bright field and fluorescence images of the outlets showing the separate reservoirs into which RBCs and leukocytes are collected.