Figure 2.

Equilibrium separation by ratcheting magnetophoresis on gradient-pitch permalloy arrays. (a) Ratcheting of 2.8μm diameter particles (IO content 10.1pg) within the chip demonstrate bimodal transport behavior dependent on the array pitch. (b) When P ≤ P_crit the particle speed correlates linearly with frequency, but when P > P_crit particles will trap and concentrate on the pillar edge. (c &d) Fluorescently labeled particle mixtures of green 1μm diameter and red 4.6μm diameter (IO contents of 0.98 and 11.1pg respectively) were separated on a 10μm increment chip ratcheted at 30Hz. 83% of the 1μm particles equilibrated at the 10μm pitch and 92% of the 4.6μm particles equilibrated at the 20μm increment patch, demonstrating a >90% separation purity. (e & f) Particle mixtures of blue 2.8μm, green 4.6μm and red 5μm (IO contents 10.1, 11.1 and 67.4 pg respectively) were separated on a 2μm pitch increment chip at 30Hz. 77% of the 2.8 and 41% of the 4.6μm particles equilibrated in the 20μm pitch region. An additional 41% of the 4.6μm particles occupied the 22μm pitch region while 85% of the 5μm particles collected at 26 and 28μm pitches.