Three independently built diamond sensors recorded the heart's magnetic field at room temperature

An NV center is a gap in the diamond lattice sitting directly next to a nitrogen atom that has taken a carbon's place ^[5]. Its energy levels respond to what surrounds it, and reading them gives magnetic and electric fields, temperature and mechanical stress with high precision ^[6]. That is why the hardware can be small: the sensitive part is the crystal. Take the cube root of half a cubic millimetre and you get 0.79, so an equivalent cube would sit under 0.8 mm on a side ^[21].

Two of the three instruments applied a magnetic bias field to filter out interference from their surroundings, and one did not ^[22]. The one that did not is the Mainz fiber-based magnetometer, built as a portable endoscope ^[8].

Magnetocardiography demands very sensitive magnetometers, and that requirement is what has tied it to costly, complex instruments such as SQUIDs and optically pumped magnetometers ^[12]. The phys.org account of the study does not state the sensitivity the three diamond systems achieved ^[20]. Room-temperature operation is demonstrated ^[10]. Whether a diamond probe resolves a cardiac trace as well as a SQUID, which does not run at room temperature ^[10], decides whether one can stand in for the other.

Arne Wickenbrock, who coordinates the DIAQNOS project from Mainz ^[2], dated the effort. "These results are the product of over 10 years of development work," he said ^[16]. He described the group's approach as working "closely with neurosurgeons to ensure that our technologies do not remain confined to the laboratory but find clear practical applications" ^[17]. Of the sensors themselves, he said they are "characterized by fast initialization, excellent biocompatibility and stable operation over a wide temperature range" ^[18].

The comparison the group draws is with electrodes. ECG is the widely used method and it is susceptible to the differing conductivity of body tissues; on burn wounds, electrodes cannot be placed on the skin at all ^[13]. A magnetic measurement needs no contact and is only minimally affected by conductivity ^[11]. The researchers also name myocarditis and epilepsy as conditions a sensitive enough sensor could catch early, and they frame those as possible future uses ^[15].