Researchers have developed a quantum sensing method using a nitrogen-vacancy (NV) center in single nanodiamond sensors, enabling the identification and evaluation of molecules in physiological in situ settings, a crucial goal in biological sciences. This method offers high sensitivity and biocompatibility. However, analyzing the movement of nanodiamonds in real cells reveals that they rotate at random both inside and on the cell membrane, rendering the existing conventional magnetic resonance detection methods worthless.
The research team devised an amplitude-modulation sequence to generate a series of equally spaced energy levels on the NV core to tackle this difficulty. When the NV center’s energy level matches the measured target’s energy level, resonance occurs, and the NV center’s state changes. The electron paramagnetic resonance (EPR) spectroscopy of the target can be obtained by scanning the modulation frequency, and the spatial orientation of the NV center no longer impacts the position of the spectral peak.
In this study, the ions in the nanodiamond solution environment were evaluated using EPR spectroscopy in situ. To detect the solution of oxygen vanadium ions, the research team recreated the movement of nanodiamonds in the cell.
When there is nanodiamond rotation, accurate quantum manipulation of NV centers is difficult, but the zero-field EPR spectrum of oxo-vanadium ions can still be detected.
This discovery shows that it is theoretically possible to employ the NV center in single nanodiamond sensors to detect intracellular physiological in-situ magnetic resonance. The oxygen vanadium ions discovered in this study have biological roles. The EPR spectrum acquired by a single moving nanodiamond can be used to evaluate and get the ultra-fine constant of oxygen vanadium ions. Previously, the research team relaxed the detection parameters of single-molecular magnetic resonance detection from solid conditions to an aqueous solution environment, and this work has advanced it to the in situ environment.
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