An open-source automated magnetic optical density meter for analysis of suspensions of magnetic cells and particles

We present a spectrophotometer (optical density meter) combined with electromagnets dedicated to the analysis of suspensions of magnetotactic bacteria. The instrument can also be applied to suspensions of other magnetic cells and magnetic particles. We have ensured that our system, called MagOD, can be easily reproduced by providing the source of the 3D prints for the housing, electronic designs, circuit board layouts, and microcontroller software. We compare the performance of our system to existing adapted commercial spectrophotometers. In addition, we demonstrate its use by analyzing the absorbance of magnetotactic bacteria as a function of their orientation with respect to the light path and their speed of reorientation after the field has been rotated by 90 degrees. We continuously monitored the development of a culture of magnetotactic bacteria over a period of 5 days and measured the development of their velocity distribution over a period of one hour. Even though this dedicated spectrophotometer is relatively simple to construct and cost-effective, a range of magnetic field-dependent parameters can be extracted from suspensions of magnetotactic bacteria. Therefore, this instrument will help the magnetotactic research community to understand and apply this intriguing micro-organism.

Automated summary

This article presents a spectrophotometer combined with electromagnets for analyzing suspensions of magnetotactic bacteria, as well as other magnetic cells and particles. The system, named MagOD, can be easily replicated, and its performance is compared to existing commercial spectrophotometers. The authors demonstrate the use of MagOD by analyzing the absorbance of magnetotactic bacteria based on their orientation and reorientation speed. The instrument allows researchers to extract various magnetic field-dependent parameters from the suspensions, aiding in the understanding and application of these intriguing microorganisms.