Magnetometry of neurons using a superconducting qubit

Iron plays important physiological and pathological roles in the human body. However, microscopic analysis including redox status by a conventional electron spin resonance (ESR) spectrometer is difficult due to limited spatial resolution and sensitivity. Here we demonstrate magnetometry of cultured neurons on a polymeric film using a superconducting flux qubit that works as a sensitive magnetometer in a microscale area towards realizing ESR spectroscopy. By changing temperature (12.5–200 mK) and a magnetic field (2.5–12.5 mT), we observe a clear magnetization signal from the neurons that is well above the control magnetometry of the polymeric film itself. From ESR spectrum measured at 10 K, the magnetization signal is identified to originate from electron spins of iron ions in neurons. This technique to detect a bio-spin system can be extended to achieve ESR spectroscopy at the single-cell level, which will give the spectroscopic fingerprint of cells. Iron is one of the most abundant trace elements in the human body, however, detection at a single-cell level with redox status is challenging. Here, the authors demonstrate magnetometry of neurons with a microscale magnetometer using a superconducting flux qubit, and Fe (III) ions in the cells are identified at a single-cell level spatial resolution.