Saturday, July 2, 2022

Quantum Diamond Microscope to Image Magnetic Fields

Researchers tap fluorescence changes in special, diamond sensor to image time-varying regions

Researchers tap fluorescence changes in special, diamond sensor to image time-varying regions

Researchers at the Indian Institute of Technology (IIT) in Mumbai and Kharagpur have created a microscope that can image magnetic fields within microscopic two-dimensional samples that change in milliseconds. This has a great potential for scientific applications, such as measuring the biological activity of neurons and the dynamics of vortices in superconductors. The work, led by Professor Kasturi Saha from the Department of Electrical Engineering, IIT Bombay, is published in scientific report. This is the first time that such an instrument has been built to image magnetic fields that change within milliseconds.

capturing change

Ms. Saha explains that the ideal frame rate to capture a changing magnetic field is one that captures data at twice the frequency of the changing field. Signals in nature exhibit a range of frequencies – magnetism in geological rock samples and rare earth magnets can be stable over months; The aggregation of magnetic nanoparticles inside living cells occurs within minutes; Action potentials in neurons are rapid, taking milliseconds, whereas in complex molecules the precession of nuclear spin only takes microseconds. The device this team has built works in the millisecond range.

The key aspect of this sensor is the “nitrogen vacancy (NV) defect center” in diamond crystals. Such NV centers act as pseudo-atoms with electronic states that are sensitive to their surrounding fields and gradients (magnetic field, temperature, electric field and strain).

“Specifically, the fluorescence emanating from these NV centers encodes magnetic field information,” says Ms. Saha. “During the measurement of ultra-small magnetic fields, the change in fluorescence levels is extremely small and, therefore, limits the imaging frame rate and reduces the signal-to-noise ratio of the measurement.”

To overcome this limitation, the researchers employed a “lock-in detection scheme”, which selects light fluctuations of a small frequency range, rejects others, and thereby allows small changes in fluorescence. improves the sensitivity of

better frame rate

The previously reported magnetic field imaging frame rates were close to 1–10 min per frame. This will increase to about half an hour per frame for challenging samples such as biological cells. The instrument produced by this group exhibits an imaging frame rate of approximately 50–200 frames per second, which would translate into a frame acquisition time of approximately 2–5 milliseconds. “This could enable the detection of millisecond scale magnetization changes in micro-magnets, dynamic micro scale thermometry in cells and further improvements in mammalian neurons,” says Ms. Saha.

A special diamond crystal, one micrometer thick, embedded with a high density of such NV centers is created. It acts as a sensor when a thin two-dimensional sample is brought close to it – less than 10 micrometers. Using this technique, researchers can image 150 micrometers across an area of ​​150 micrometers, which is quite an achievement.

“The NV center imaging technique is a unique tool in terms of imaging the subtle magnetic field variations in any sample,” says Ms. Saha.

The team started collaboration with IIT Kharagpur in 2017 with the ambitious goal of creating a new system to image the brain. He collaborated with Sharba Bandyopadhyay, who specialized in neurobiology and bioengineering, to complement the knowledge of quantum optics, quantum computing and quantum sensing, which Ms. Saha characterized.

“We, in collaboration with PhD student Madhur Parashar, have developed an algorithm to image neurons in 3D using NV quantum sensors,” says Ms. Saha.

This work. was published in communication physics in 2020. We have jointly filed a patent for the present work, she adds.

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