Abstract
Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centres in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centres, demonstrating magnetic field sensitivity of approximately 100 pT/$\sqrt{Hz}$ in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated.
Highlights
Many biological processes generate electrical signals, for example synaptic transmission and muscular contraction
We use an inverted microscope geometry, where laser excitation and light collection is performed with the diamond held on a raised platform, above a microwave antenna board and below a custom-3D printed bath chamber for holding a biological sample (C and D, Figure 1), with the solution fed via capillary tubes (I) from a peristaltic pump
By using field coils to generate a counter field to the noise, can reduce it but this is hard to achieve for multi-axis sensing at a small √1–2 mm diamond, at kHz bandwidth and operating at sub-nT/ Hz sensitivity
Summary
Many biological processes generate electrical signals, for example synaptic transmission and muscular contraction. Such signals give key information on the functioning on biological systems, either for clinical diagnostic purposes (such as electrocardiography) or for fundamental understanding of processes and structure. Measuring these signals is typically performed using electrical probes carefully positioned in the desired region. This poses difficulties if this region is not accessible, such as inside the brain, or where signals must be highly spatially resolved. Existing techniques for this, such as magnetoencephalography (MEG) or magnetocardiography (MCG) are limited by reliance on superconducting quantum
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