Plant biomagnetism and magnetic resonance with atomic magnetometry

Abstract

This thesis explores the unique intersection of two subjects, magnetic fields and living plants, using the tool of atomic magnetometry. The choice of tool, also known as optical magnetometry or optically pumped magnetometry, is motivated by the relatively weak (sub-picotesla) fields under study. Atomic magnetometers have emerged in recent years as the most sensitive human-made magnetic-field detectors, rivaling even superconductingquantum-interference-device (SQUID) magnetometers. Because atomic magnetometers are noncryogenic, miniaturizable, and can be engineered for portability, they lend themselves to diverse practical applications and have so far been commercialized for biomedicine and geophysics. However, from existing technical literature it has not necessarily been straightforward to understand exactly how these devices fit into the wider landscape of magnetometry, as well as their various different operating principles. To this end, we begin with a tutorial on the physics of atomic magnetometry and review the state of the field. Then, two different plant-based lines of research are described. The first experiment focuses on plant biomagnetism, i.e. magnetic fields produced by electrical activity in living plants. We detect the magnetic component of the action potential (AP) from the Venus flytrap, a beloved carnivorous plant, employing heat transfer from the thermal sensor to induce autonomous AP firing. This work opens the door to noninvasive studies of current distributions and long-distance electrical signaling in plants and fungal networks, not fully possible using traditional electrophysiological techniques. The second experiment involves construction and testing of a zero-to-ultralow-field nuclear-magnetic-resonance (ZULF-NMR) spectrometer with a novel signal-enhancing detection scheme. This setup is applied to monitor water dynamics in intact tree leaves, tracking water content and proton-relaxation behavior as a function of dehydration and tree genus. Other applications of the setup are also briefly presented.