Determination of the magnetic susceptibility of labeled particles by video imaging

Abstract

Magnetic cell sorting is gaining in popularity as a method to separate and recover viable cells which differ in functionality, but not in physical characteristics. We are developing a continuous cell sorter to overcome the restrictions of current batch methods, which are limited in their throughput and separation efficiency and which can also subject cells to potentially detrimental physical stresses. Of primary importance in the design and operation of a continuous magnetic cell sorter is the degree of cell magnetization, which is characterized by a property called the magnetic susceptibility. Current techniques for measuring susceptibility give only population average values. We describe here a video-based technique for quickly measuring the susceptibility of large numbers of individual particles. Paramagnetic particles are pumped across the interpolar gap of a permanent magnet and the magnetic field-induced deflections are recorded by video microscopy. Susceptibility is computed from force balances and the measured velocities for individual particles. Our results show that this method can provide susceptibility values which agree well with values obtained from other established methods, while additionally providing population statistics not available by the other methods. The versatility of this method is also demonstrated.