Patent ID: 7829350

Claim:
A method for determining the presence of a target molecule in a sample, the method comprising obtaining a mixture of at least two different populations of conjugates that specifically bind to the target molecule to form an aggregate, wherein each conjugate in the first population comprises a nanoparticle comprising a magnetic metal oxide linked to a plurality of first binding moieties that bind to a first binding site on the target molecule, and wherein each conjugate in the second population comprises a nanoparticle comprising a magnetic metal oxide linked to a plurality of second binding moieties that bind to a second binding site on the target molecule different than the first binding site; contacting the mixture with a fluid sample under conditions that enable the first and second binding moieties to specifically bind to any target molecules in the sample and form an aggregate of conjugates; and determining the presence of one or more aggregates in the sample by measuring the spin-spin (T 2 ) relaxation time of the fluid sample, wherein the one or more aggregates remain in solution for at least the duration of the T 2 measurement, wherein an increase in the number of aggregates within the fluid sample reduces the measured T 2 relaxation time, and wherein a decrease in the T 2 relaxation time of the fluid indicates the presence of the target molecule in the sample.