Diagnostics with magnetic nanoparticles: the VAM-NDA method
Figure caption: Schematic illustration of the volume-amplified magnetic nanobead detection assay. A collection of single-stranded target DNA molecules are indicated in blue. After addition of matching padlock probes (grey), circularized padlock probes form upon hybridization and the ends of the padlock probe molecules are joined together by ligation. The circularized padlock probes are then amplified by the RCA mechanism, creating random-coiled DNA macromolecules. To detect the presence of RCA products, single-stranded oligonucleotidefunctionalized magnetic beads (brown) are added, which are incorporated by base pair hybridization to the RCA coils. The bead incorporation results in a spectrum of the complex magnetization (positive sample, blue magnetization curve) substantially different from the response of a sample containing free beads only, i.e., the absence of RCA products (negative sample, green magnetization curve). The two relaxation events in the blue curve have been resolved (bold black curves) using a Cole–Cole fitting procedure, and the peak frequency values are indicated.