Magnetically Levitated Plasma Proteins.

Surprisingly, the densities of proteins in solution, which are important fundamental biophysical quantities, have not been accurately measured. The lack of such data can limit meaningful interpretation of physical and chemical features of proteins and enzymes. Here, we demonstrate a new technique using superparamagnetic iron oxide nanoparticles (SPIONs) for magnetic levitation (MagLev), which promises to more precisely measure the density of proteins in solution. As a test of our new technique, we have levitated human plasma proteins using MagLev. By using standard density glass beads for calibration, MagLev showed that the levitated plasma proteins have a measured density in solution of 1.03 ± 0.02 g/cm3, which is much lower than those reported or assumed in the past literature (i.e., ∼1.35 g/cm3). Our findings suggest that MagLev may provide useful insights into the measurement of densities for better understanding the solution properties of proteins and their interactions both with other proteins in solution and with solvating water molecules.