We characterized the properties of magnetic markers for liquid phase immunoassays using Brownian relaxation. Since magnetic markers are usually composed of aggregated magnetic nanoparticles, their properties are significantly affected by the degree of aggregation. Through the analysis of magnetization (M-H) and AC susceptibility measurements, we obtained the distribution of the magnetic moment m and the Neel relaxation time τN of the aggregated particles included in the markers. We also determined the relationship between m and τN. From the obtained result, we could classify the particles into three types: Type-1 particles with very small m and very short τN , Type-2 particles with medium values of m and τN, and Type-3 particles with large m and very long τN. The proportion of these three types of particles included in the marker was also evaluated. We show that Type-3 particles and some Type-2 particles with τ N > τB are primarily responsible for the observed signal in the liquid phase immunoassay using Brownian relaxation, where τB is the Brownian relaxation time. The obtained results are useful for evaluating suitable markers for liquid phase immunoassays using Brownian relaxation.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Electrical and Electronic Engineering