Published in Review of Scientific Instruments, Volume 72, Issue 6, June 1, 2001, pages 2724-2730.
Copyright © 2001 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments and may be found at http://dx.doi.org/10.1063/1.1361079.
An electronic control system for the measurement of hysteresis curves of microscopically observed magnetic structures such as chains of magnetosomes in magnetotactic bacteria suspended or swimming in water is described. Using continuous magnetic fields generated by four coils for guidance or orientation of the bacteria or other magnetic structures, and pulsed magnetic fields in two additional coils for changing the degree of magnetization in small steps, hysteresis curves can be traversed. The circuits described can be constructed with readily available components. The guiding- and pulsed-field coils can be fashioned in any standard machine shop. The typical sensitivity of the system is better than 10−12 ergs/G, which makes a wide range of bacteria accessible to quantitative measurement of their magnetosome chains. The electronic circuits as well as the coil systems are described in detail.