Patent ID: 8354234

Claim:
A method of assaying a target analyte in a sample comprising the steps of: a) providing a composition comprising antibody-conjugated magnetic nanoparticles (Ab-mNPs), wherein each of the Ab-mNPs comprises: i) a core iron oxide nanoparticle ranging in size from 0.1 to 500 nm; ii) cross-linkers, covalently conjugated to the surface of the core nanoparticle; iii) antibody molecules specific for a target analyte, covalently conjugated to the cross-linkers; and iv) methoxy ethylene glycol having the structure H 3 C—O—CH 2 CH 2 —O—CH 2 CH 2 —O—CH 2 CH 2 —NH 2 covalently conjugated through the amine group to cross-linkers that are unconjugated to the antibody molecules; b) exposing a sample that may contain the target analyte to the Ab-mNPs to allow the target analyte to be captured by the Ab-mNPs; c) subjecting the Ab-mNPs and the sample from step (b) to a magnetic field to separate the Ab-mNPs and the captured target analyte from the rest of the sample; and d) performing mass spectrometry on the Ab-mNPs and the captured target analyte from step (c) to obtain a mass spectrum for assaying the target analyte; wherein the target analyte is a compound selected from the group consisting of a protein, a polypeptide and a peptide.