Background defocusing and clearing in ferrofluid-based capture assays

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;
• capturing the plurality of target particles on a surface of a capture region via binding to capture molecules;
• and
• 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.

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;
• a plurality 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,
• a capture region arranged on a surface of the microchannel and 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, whereby 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 which have collected there without removing the target particles bound to the capture molecules.

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,
• wherein:
• the electrodes configured to generate a first magnetic field and a second magnetic field, and
• 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, wherein the defocusing excitation is configured to clear particles which collect in the capture region which do not bind with one or another of the plurality of capture molecules.