Superparamagnetic nanoparticles (MNPs) have been utilized in biomedical sensing, detection, therapeutics, and diagnostics due to their unique magnetic response under different driving fields. In this letter, we report a multi-tracer tracking method that uses different kinds of MNPs as magnetic tracers along with two alternating magnetic fields that can be potentially used to build magnetic-based flow cytometry. By applying two driving fields at frequency f H and f L to MNPs, the response signal is measured at the combinatorial frequencies such as fH ï¿½ 2 fL(3rd harmonics), fH ï¿½ 4 f L (5th harmonics), fH ï¿½ 6 f L (7th harmonics), and so on. Each MNP has its own signature of phase and amplitude, and it is possible to differentiate individual MNPs in a mixture. We theoretically demonstrated colorizing up to 4-MNP tracers in one mixture with an error rate lower than 10%. The performance of multi-tracer imaging can be optimized by increasing the driving field frequency, choosing MNPs with higher saturation magnetization, and using MNP tracers with more centralized size distribution.
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