Background defocusing and clearing in ferrofluid-based capture assays

A system for extracting target particles from a ferrofluid, the system comprising:

• a microchannel configured to receive a flow comprising a plurality of target particles and background particles in a ferrofluid;
• at least two sets of electrodes arranged proximate the microchannel, the at least two sets of electrodes configured to generate a first magnetic field and a second magnetic field, wherein
• the first magnetic field corresponds to a focusing excitation and the second magnetic field corresponds to a defocusing excitation,
• the focusing excitation generated by a first of the at least two sets of electrodes generating a first alternating current and a second of the at least two sets of electrodes generating a second alternating current, wherein the first alternating current is out of phase with the second alternating current by a phase differential,
• the defocusing excitation generated by reversing the phase differential of the focusing excitation;
• and
• a capture region functionalized with a plurality of capture molecules, each capture molecule configured to bind with one target particle, wherein
• the focusing excitation focuses the flow of target particles toward the capture region, wherein a plurality of the target particles bind with the capture molecules and a plurality of unbound background particles collect in the capture region, and
• the defocusing excitation removes the unbound background particles from the capture region without removing the target particles bound to the capture molecules;
• and
• a detector to detect the bound target particles.

A system for extracting target particles from a ferrofluid, the system comprising:

• a microchannel configured to receive a plurality of target particles and background particles in a ferrofluid;
• a plurality of electrodes arranged proximate the microchannel, the electrodes configured to generate a first magnetic field and a second magnetic field, wherein the first magnetic field corresponds to a focusing excitation and the second magnetic field corresponds to a defocusing excitation;
• and
• a capture region functionalized with a plurality of capture molecules, each capture molecule configured to bind with one target particle.

A method for extracting target particles from a ferrofluid, the method comprising:

• receiving a plurality of target particles and background particles in a ferrofluid in a microchannel;
• generating a first magnetic field corresponding to a focusing excitation from a first set of electrodes;
• capturing a plurality of target particles in the capture region via the binding of the target particles with the capture molecules, wherein a plurality of unbound particles collect in the capture region;
• generating a second magnetic field corresponding to a defocusing excitation to remove unbound particles from the capture region without removing target particles bound to the capture molecules.