Integrated microfluidic isolation platform for magnetic particle manipulation in biological systems

We have developed a micromachined fluid-cell platform that consists of patterned magnetic thin-film elements supported on a thin silicon-nitride membrane. In the presence of an external magnetic field, the field gradients near the magnetic elements are sufficiently large to trap magnetic particles that are separated from the patterned films by a 200 nm thick nitride membrane. The two main applications of this fluid-cell platform are to provide a means to control and position magnetic microparticles, which can be tethered to biological molecules, and also to sort superparamagnetic microparticles based on their size and magnetic susceptibility. We determine the characteristic trapping forces of each trap in the array by measuring the Brownian motion of the microparticle as a function of applied external field. Typical force constants and forces on the superparamagnetic particles are 4.8x10(-4)+/-0.7x10(-4) N/m and 97+/-15 pN, respectively.