Modification of ferrography method for analysis of lymphocytes and bacteria

Abstract Problems associated with the analysis of low magnetically susceptible or diamagnetic biological particles in ferrography are related to the unoptimal fluid dynamics, the low magnetic field strength and gradients and the lack of effective magnetizing agents. Flow geometry optimization in slide ferrography has been undertaken with the specific aims of obtaining a thinner flow channel, better-defined fluid flow geometry, uniform distribution of particles within the flowing volume, containment of the flowing liquid sample, exposure of all flowing particles to the magnetic field, and differentiation of deposition layers formed by different forces, i.e. magnetic, gravitation and flow related. These specific aims were attained by adopting a novel slide scheme which at present reduces the fluid flow thickness by tenfold and increases the peak relative magnetostatic force by up to three orders of magnitude, compared with the conventional slide ferrography. The novel slide ferrography scheme, combined with the use of the strongest permanent magnet available, is better suited to the analysis of biological particles than conventional ferrography is. Where native mononuclear blood cells showed no response to the magnetic field when treated with erbium, mononuclear cells which had been cultured for as short as 24 h and as long as 72 h show magnetically induced deposition after erbium treatment. Non-specific labeling with cationized ferritin causes the magnetic deposition of all cells studied, i.e. native and cultured human lymphocytes, and mouse lymphoma cells (YAC-1). Modified slide ferrography shows that the bacterium Escherichia coli has a high affinity for erbium ions and becomes readily magnetized and separated. Observations of bacterial magnetic deposition are possible in unstained slide mounts using scattered light. Scattered-light intensity correlated with the bacterial cell concentration in the samples analyzed by ferrography.