Magnetic nanoparticles for novel biodetection assay techniques

Abstract: Water-based suspensions of single-core iron-oxide particles with nominal sizes 15 - 50 nm were studied by AC and DC magnetometry techniques, in order to determine their suitability for use in the volume amplified nanobead detection assay (VAM-NDA). The VAM-NDA can detect specific bio molecules, which have been magnetically tagged and volume amplified, by measuring the difference in the Brownian relaxation rate compared to a negative control sample. Single-core nanoparticles are expected to have a stronger low-field magnetic response, narrower size distributions and to better be described by the theoretical model constituting the foundation of the VAM-NDA, as opposed to particles consisting of a multi-grained cluster embedded in a non-magnetic coating, which previously have been used in the assay. Experiments showed that all particles exhibit signs of spin disorder, including a diminished magnetic response. The particles with nominal core diameters 25, 30 and 40 nm were superparamagnetically blocked at room temperature and were very narrowly distributed in size. Therefore, in spite of their diminished magnetic response, they could be useful for improving the assay.