Background defocusing and clearing in ferrofluid-based capture assays

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

receiving a flow within a microchannel, the flow comprising a plurality of target particles and background particles in a ferrofluid;

generating a first magnetic field corresponding to a focusing excitation, the first magnetic field generated by at least two sets of electrodes arranged proximate the microchannel,

wherein

a first of the at least two sets of electrodes generates a first alternating current and

a second of the at least two sets of electrodes generates a second alternating current, wherein

the first alternating current is out of phase with the second alternating current by a phase differential;

the focusing excitation is configured to focus the flow of a plurality of target particles to a surface of a capture region, and

the surface of the capture region is functionalized with capture molecules each configured to bind with a target particle;

capturing a plurality of target particles on the surface of 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, different from the first magnetic field and after generation of the first magnetic field, the second magnetic field corresponding to a defocusing excitation,

wherein

the second magnetic field is generated by reversing the phase differential between the first alternating current and the second alternating current, and

the defocusing excitation is configured to remove unbound particles from the capture region without removing target particles bound to the capture molecules; and

detecting the bound target particles via a detector.

2. The method of claim 1 , wherein the detector is one of: an automated scanning microscope, a sensitive mass balance, and an electrochemical sensor.

3. The method of claim 1 , wherein the phase differential between the first alternating current and the second alternating current is 90°.

4. The method of claim 3 , wherein the focusing excitation caused by the first magnetic field rotates the particles in a particular direction.

5. The method of claim 4 , wherein the rotation of the particles in the particular direction causes the particles to focus.

6. The method of claim 3 , wherein the reverse phase differential between the first alternating current and the second alternating current is −90°.

7. The method of claim 6 , wherein the defocusing excitation caused by the second magnetic field rotates the particles in a second particular direction, wherein the rotation in the second particular direction causes the particles to defocus.

8. The method of claim 1 , wherein the phase differential is determined using a total number of sets of electrodes used, such that the phase differential is +180 divided by the number of sets of electrodes and the reverse phase differential is −180 divided by the number of sets of electrodes.

9. 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 on a surface of a capture region, the surface of the capture region being functionalized with capture molecules, wherein:

the capture molecules bind with the target particles, and

a plurality of unbound particles collect in the capture region;

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.