In the project, a measurement setup will be developed which, by combining optically pumped magnetometers (OPM) and microfluidics (MF), allows for the first time to individually determine the magnetic moments of magnetosomes or magnetotactic bacteria (MTB) - hereinafter collectively referred to as magnetic microparticles - during the throughput of larger quantities. This measurement setup has relevance both for the characterization of MTB populations and for the characterization of biogenically produced magnetic nanoparticles. For the realization of this goal, physical working principles of OPM and MF are to be suitably selected, adapted and implemented in terms of instrumentation. The applicability will be demonstrated exemplarily in the final investigation of MTB populations.
The optically pumped magnetometers represent the core of the measurement setup. Their measuring principle is based on polarizing alkali atoms in the gas phase in an optical pumping process and measuring their interaction with the magnetic field B0. In the Mx mode used here [Bloom, 1962; Alexandrov, 1996; Groeger, 2006], pumping is performed with circularly polarized light, which aligns the spins of the alkali atoms in the propagation direction of the pump light. As a consequence of the interaction with the measurement field, which is preferably inclined at 45° to it, the spins precess with the Larmor frequency fL =γ∙B0 around the field direction. Here γ is the gyromagnetic ratio of the alkali atom used (3.5 kHz/μT for the cesium we used). The precession of the spins of the atoms is readily measurable as a modulation of the pump light at the Larmor frequency when they are synchronized in phase. We will use a magnetic field oscillating with the Larmor frequency, the so-called B1 field, for this purpose [Bloom, 1962], because this offers the possibility to use special noise reduction mechanisms developed at our institute (see below).

The project is supported by DFG grant number SCHU 2845/3-1; AOBJ: 638324.