Magnetic levitation of nanoscale materials: the critical role of effective density

Abstract

The magnetic levitation (MagLev) of diamagnetic materials in a paramagnetic solution is a robust technique for the density-based separation, measurements, and analysis of bulk materials/objects (e.g., beads and plastics). There is a debate in the literature, however, about whether a MagLev technique is reliable for the separation and/or density measurements of nanoscale objects. Here, we show that MagLev can levitate nanoparticles; however, the transition from the bulk to an ‘effective’ density must be acknowledged and considered in density measurements at the nanoscale regime. We performed a proof-of-concept study on MagLev’s capability in measuring the ‘effective density’ of multiscale silver particles (i.e. microparticles, nanopowder, and nanoemulsion). In addition, we probed the effective density of nanoscale biomolecules (e.g. lipoproteins) using a standard MagLev system. Our findings reveal that the MagLev technique has the capability to measure both bulk density (which is independent of the size and dimension of the material) and the effective density (which takes place at the nanoscale regime and is dependent on the size and surrounding paramagnetic solution) of the levitated objects.