Highly Sensitive Quantum Magnetometry for Tracing Magnetotactic Bacteria Behavior in the Microfluidic Chip.

Magnetotactic bacteria (MTB) possess intrinsic magnetic navigation via chain-organized magnetosomes, enabling targeted transport in complex biological environments. There is a lack of techniques for MTB drug transport evaluation based on precise behavior monitoring. Here, we proposed a nanotesla-level magnetic detection method for dynamic MTB behavior tracing, which has a sensitivity of 21.6 nT/√Hz under ambient conditions, enabling robust signal acquisition even at very low cell density. This capability was realized by a biocompatible microfluidic-quantum sensing platform that couples a diamond nitrogen-vacancy (NV) center probe with a vascular-mimicking microchannel and a microwave antenna. By linking magnetic signal evolution with bacterial motility, three quantitative indicators were identified, including fitting quality, the early-stage growth rate of the magnetic signal, and the peak rate of signal change. These indicators enabled the predictive classification of enrichment dynamics and guided regulation strategies. This label-free, real-time, and biocompatible framework provides a powerful tool for behavior-resolved analysis of MTB and offers a scalable route toward closed-loop, magnetically guided drug delivery.