Hyper-high-sensitivity wash-free magnetoreduction assay on biomolecules using high-Tc superconducting quantum interference devices

In this work, we develop a platform for assaying biomolecules involving the measurement of alternating current (ac) magnetoreduction of magnetic reagent mixed with a detected sample. The magnetic reagent contains magnetic nanoparticles coated with a given kind of antibody, which associates with conjugated biomolecules. Then, the biomolecules can be quantitatively detected by measuring the ac magnetoreduction of magnetic reagent. To achieve hyper-high-sensitivity assay, a system utilizing a high-transition-temperature rf superconducting quantum interference device (SQUID) as a sensor to probe the magnetoreduction of reagent due to the association between biomolecules and magnetic nanoparticles. Examples to assay multiactive epitope, single-active epitope, and small molecules are given to demonstrate the validity of the assay platform, as well as the hyper-high sensitivity.