Self-Assembled Magnetic Nanoparticle–Graphene Oxide Nanotag for Optomagnetic Detection of DNA

In this work, a two-dimensional self-assembled magnetic nanoparticle–graphene oxide (MNP-GO) nanocomposite is reported for the detection of DNA. Single-stranded DNA (ssDNA) coils, generated through a rolling circle amplification (RCA) reaction triggered by the hybridization of target oligos and padlock probes, have a strong interaction with MNP-GO nanotags through several mechanisms including π–π stacking, hydrogen bonding, van der Waals, electrostatic, and hydrophobic interactions. This interaction leads to a hydrodynamic size increase or aggregation of MNP-GO nanotags, which can be detected by a simple optomagnetic setup. Due to the high shape anisotropy, MNP-GO nanotags provide stronger optomagnetic signal than individual MNPs. Moreover, the avoidance of DNA probes (i.e., short ssDNA sequences as the biosensing receptor) provides easier material preparation and lower measurement cost. From real-time measurements of interactions between MNP-GO and RCA products amplified from a highly conserved Escherich...