Ultralow detection limit of giant magnetoresistance biosensor using graphene composite nanoparticle label**Project supported by the National Natural Science Foundation of China (Grant Nos. 11074040, 11504192, 11674187, 11604172, and 51403114), the Natural Science Foundation of Shandong Province, China (Grant Nos. ZR2012FZ006 and BS2014CL010), and the China Postdoctoral Science Foundation (Grant Nos. 2014M551868 and 2015M570570).

Abstract

A special Fe3O4 nanoparticles–graphene (Fe3O4–GN) composite as a magnetic label was employed for biodetection using giant magnetoresistance (GMR) sensors with a Wheatstone bridge. The Fe3O4–GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization of approximately 48 emu/g, coercivity of 200 Oe, and remanence of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe3O4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe3O4–GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference between detecting and reference sensors undergoes the relationship of with an ultralow detection limit of 10 ng/mL (very close to the calculated limit of 7 ng/mL) and a wide detection range of 4 orders.