Fig. 1.

Using particle trajectory analysis (PTA) to observe particle focusing behavior in diluted blood. (a) Randomly distributed particles predominantly focus to two lateral positions centered on the long face of a straight microchannel with 2 : 1 aspect ratio. (b) The equilibrium positions result from a balance of a “wall effect” lift that acts away from the wall towards the channel centerline and a “particle shear” lift that acts away from the channel centerline towards the wall. (c) Particle focusing behavior is observed in the x–z plane from eight different vertical positions spanning the bottom half of the channel. Focused particles are shown to be in focus at y₈ = 48 µm (scale bar = 20 µm). (d) For high-speed bright-field (HSB) microscopy with an exposure time of 2 µs, individual white blood cells can be identified in physiological saline (f_RBC = 0) but not in diluted blood (f_RBC = 0.07). For long-exposure fluorescence (LEF) microscopy with an exposure time of 1 s, a bulk white blood cell distribution profile can be identified, but the profile cannot be de-constructed based on height position or particle diameter. For particle trajectory analysis (PTA) with an exposure time of 10 ns, individual white blood cells re-suspended in physiological saline or diluted blood can be identified at multiple vertical positions in the channel (scale bar = 20 µm). (e) At a flow rate Q = 450 µl min⁻¹, PTA images of polystyrene beads (R_p = 2.91 for f_RBC = 0), white blood cells (R_p = 2.41 for f_RBC = 0), and PC-3 prostate cancer cells (R_p = 9.11 for f_RBC = 0) suspended in physiological saline and diluted blood demonstrate that individual in-focus particles can be identified in starting samples with higher RBC volume fractions (f_RBC) without significant degradation in fluorescence signal quality.