Detection of biological signals from a live mammalian muscle using an early stage diamond quantum sensor

Abstract

The ability to perform noninvasive and non-contact measurements of electric signals produced by action potentials is essential in biomedicine. A key method to do this is to remotely sense signals by the magnetic field they induce. Existing methods for magnetic field sensing of mammalian tissue, used in techniques such as magnetoencephalography of the brain, require cryogenically cooled superconducting detectors. These have many disadvantages in terms of high cost, flexibility and limited portability as well as poor spatial and temporal resolution. In this work we demonstrate an alternative technique for detecting magnetic fields generated by the current from action potentials in living tissue using nitrogen vacancy centres in diamond. With 50 pT/$$\sqrt{\text {Hz}}$$ Hz sensitivity, we show the first measurements of magnetic sensing from mammalian tissue with a diamond sensor using mouse muscle optogenetically activated with blue light. We show these proof of principle measurements can be performed in an ordinary, unshielded lab environment and that the signal can be easily recovered by digital signal processing techniques. Although as yet uncompetitive with probe electrophysiology in terms of sensitivity, we demonstrate the feasibility of sensing action potentials via magnetic field in mammals using a diamond quantum sensor, as a step towards microscopic imaging of electrical activity in a biological sample using nitrogen vacancy centres in diamond.

In-vitro Recordings of Neural Magnetic Activity From the Auditory Brainstem Using Color Centers in Diamond: A Simulation Study

“…Although NV sensor technology is not currently able to image neural magnetic signals to allow distinguishing between different neural sources along the investigated pathway, as is currently done using e.g., fluorescent imaging, the present results suggest that detecting the neural magnetic fields by spatial averaging the field over a whole mm-sized diamond (as done by Barry et al, 2016 ; Webb et al, 2021 ) would likely be possible. In order to reach maximal field strengths, the presented model and stimulation results are highly useful for determining good sample positioning for such methods.…”

“…In this section we discuss how the simulated magnetic fields can be detected by the use of current setups of NV diamond sensors. The aim was to predict the signal from an experimental setup similar to the one described in Webb et al (2021) . However, the modeled magnetic fields are independent on the sensor setup.…”

“…However, the modeled magnetic fields are independent on the sensor setup. In an experimental NV sensor setup, as seen in e.g., ( Webb et al, 2021 ), the diamond sensor is illuminated from below with a laser with a wavelength of 532 nm (green), and the resulting fluoresce light at ∼650 nm (red) is measured which has an intensity that is directly proportional to the magnetic field. The light is collected through a 600 nm long pass filter to remove any potential interference from the blue light used for ontogenetic stimulation.…”

“…However, they have very low absorption at this wavelength, and the effect would be negligible. Furthermore, in Webb et al (2021) the light was shielded from the brain slice with a layer of reflective aluminum, so that the interferences between the two different optical setups (i.e., optogenetic stimulation from above, and NV diamond sensor excitation from below) become negligible.…”

“…Although sensitivities in the sub-pT/Hz 1/2 range have recently been reported for NV-based magnetic field sensing ( Fescenko et al, 2020 ; Zhang et al, 2021 ), measurements of biological samples so far only reached picotesla ranges. This includes 15 pT/Hz 1/2 sensitivity for measurements on an invertebrate sample ( Barry et al, 2016 ) and 50 pT/Hz 1/2 for mouse tissue ( Webb et al, 2021 ), with a noise level of 12 pT being reached after 8 h of optical stimulation at 0.5 Hz. These sensitivities are already sufficient to measure the expected signals in the range of 0.5 nT and lower.…”