Ferromagnetic Resonance Biosensor for Homogeneous and Volumetric Detection of DNA

The ability to detect and analyze the state of magnetic labels with high sensitivity is of crucial importance for developing magnetic biosensors. In this work, we demonstrate, for the first time, a ferromagnetic resonance (FMR) based homogeneous and volumetric biosensor for magnetic label detection. Two different isothermal amplification methods, i.e., rolling circle amplification (RCA) and loop-mediated isothermal amplification (LAMP), are adopted and combined with a standard electron paramagnetic resonance (EPR) spectrometer for FMR biosensing. For the RCA-based FMR biosensor, binding of RCA products of a synthetic Vibrio cholerae target DNA sequence gives rise to the formation of aggregates of magnetic nanoparticles. Immobilization of nanoparticles within the aggregates leads to a decrease of the net anisotropy of the system and a concomitant increase of the resonance field. A limit of detection of 1 pM is obtained with a linear detection range between 7.8 and 250 pM. For the LAMP-based sensing, a synthetic Zika virus target oligonucleotide is amplified and detected in 20% serum samples. Immobilization of magnetic nanoparticles is induced by their coprecipitation with Mg₂P₂O₇ (a byproduct of LAMP) and provides a detection sensitivity of 100 aM. The fast measurement, high sensitivity, and miniaturization potential of the proposed FMR biosensing technology makes it a promising candidate for designing future point-of-care devices.