Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity

Abstract

Magnetic fields generated by human and animal organs, such as the heart, brain and nervous system carry information useful for biological and medical purposes. These magnetic fields are most commonly detected using cryogenically-cooled superconducting magnetometers. Here we present the first detection of action potentials from an animal nerve using an optical atomic magnetometer. Using an optimal design we are able to achieve the sensitivity dominated by the quantum shot noise of light and quantum projection noise of atomic spins. Such sensitivity allows us to measure the nerve impulse with a miniature room-temperature sensor which is a critical advantage for biomedical applications. Positioning the sensor at a distance of a few millimeters from the nerve, corresponding to the distance between the skin and nerves in biological studies, we detect the magnetic field generated by an action potential of a frog sciatic nerve. From the magnetic field measurements we determine the activity of the nerve and the temporal shape of the nerve impulse. This work opens new ways towards implementing optical magnetometers as practical devices for medical diagnostics.The magnetic field generated around a signaling nerve fiber is of key interest both from a basic scientific and a clinical point of view. The transmembrane potentials have been extensively measured with electrophysiological techniques. Magnetic field measurements are insensitive to the transmembrane currents as the fields from the opposite currents in and out of the membrane cancel. Instead, magnetic field measurements allow for a true measurement of the axon's axial net current, which is the depolarizing wavefront driving the action potential. Magnetic field recordings also allow for non-invasive measurements of the conduction velocity of peripheral nerves 1 which is necessary for diagnostics of multiple sclerosis, myotonia and intoxication in patients.The magnetic field of a nerve impulse was first measured by Wikswo et al. 2 using a combination of a superconducting SQUID magnetometer and a toroidal pick-up coil through which the nerve had to be pulled. This method is not compatible with in vivo diagnostics and yields the magnetic field values which are much higher than that in an animal because the return currents in the surrounding tissue are not measured. Here we are able to detect the nerve impulse with the sensor placed beside the nerve, several millimeters away, the setting compatible with in vivo studies. Detection of nerve impulses with a magnetometer based on Nitrogen-Vacancy centers in diamond has recently been reported 3 . Such magnetometers seem promising for magnetic field microscopy applications where the magnetometer can be placed at micrometer distance or closer to the biological object.Sensitivity of atomic magnetometers 4 improves with the number of atoms sensing the field, which for vapor magnetometers is defined by volume and temperature. For example, femtoTesla sensitivity has been achieved with magnetometers operating at a temperature of seve...

Quantum sensing

“…Vapor cells have been miniaturized to few mm 3 small volumes (Shah et al, 2007) and have been used to demonstrate entanglement-enhanced sensing (Fernholz et al, 2008;Wasilewski et al, 2010). The most advanced application of vapor cells is arguably the detection of neural activity (Jensen et al, 2016;Livanov et al, 1978), which has found use in magnetoencephalography (Xia et al, 2006). Vapor cells also promise complementary access to high-energy physics, detecting anomalous dipole moments from coupling to exotic elementary particles and background fields beyond the standard model (Pustelny et al, 2013;Smiciklas et al, 2011;Swallows et al, 2013).…”

Reconstruction-Free Quantum Sensing of Arbitrary Waveforms

“…For slowly varying signals, the transition frequency of the sensor can be tracked in real time [13], permitting detection of arbitrary waveforms in a single shot. By using a large ensemble of quantum sensors detection bandwidths of up to ∼ 1 MHz have been demonstrated [14,15], with applications in MRI tomograph stabilization [14], neural signaling [16,17], or magnetoencephalography [18].For rapidly changing signals the waveform can no longer be tracked, and a general waveform cannot be recorded in a single shot. However, if a waveform is repetitive or can be re-triggered, multiple passages of the waveform can be combined to reconstruct the full waveform signal.…”

Effects of pressure on suspended micromechanical membrane arrays

“…Schematic sideviews of single-membrane (a) and doublemembrane (b) resonators. c) Photograph of a double-membrane resonator.ing for realizing integrated micromechanical cells for pressure sensing and ultrasound transduction applications [26], spectroscopy [27] or for collective and hybrid optomechanics [28][29][30][31][32].A schematic of the suspended membrane drums used in this work is shown in Fig. 1.…”