Magnetic Field Imaging of Superparamagnetic Particles Using High‐Density, Perfectly Oriented NV Centers in Diamond CVD Film

Abstract

The spatial and temporal resolutions of bio‐imaging with magnetic nanoparticles (MNP) as a label and a diamond substrate as a magnetic field imager are investigated. To realize fast and accurate magnetic field imaging even for a substrate with unresolved hyperfine peaks, relative fluorescence is measured at four operation points corresponding to the steepest slopes of two dips in the ODMR spectrum. The (111) diamond substrate with a 3.5‐μm thick chemical vapor deposition film with an NV− density of 1.6 × 1016 cm−3 allows us to detect 1‐μm MNPs scattered on its surface with an accumulated exposure time of 19 s under external DC magnetic field of 1.3 mT. Theoretical limit of temporal sensitivity is estimated to be more than four orders of magnitude smaller than measured. Although for measurement in culture medium, an objective lens with longer working distance is required and the condition will become somewhat worse, a spatiotemporal resolution of <1 s and <1 μm for the density and quality of the NV centers used in this study is expected if the already reported sensitivity enhancement technologies are further incorporated.

Magnetic Field Mapping Around Individual Magnetic Nanoparticle Agglomerates Using Nitrogen‐Vacancy Centers in Diamond

“…The dark features in the fluorescence images are caused by the magnetic agglomerates themselves blocking the NV center fluorescence signal on the passage toward the detector, thereby allowing the user to find the magnetic structures of interest directly in the fluorescence intensity images, rather than indirectly by their effect on the energy level splitting that can be observed after radio frequency sweeping and fitting of the ODMR traces to determine local magnetization. The direct identification of MNPA agglomerates in fluorescence intensity scans is more convenient compared with the approaches shown in Tetienne [ 28 ] and Hatano [ 29 ] due to easier access/visibility of the particles/agglomerates and thus has some advantages, despite the fact that this method cannot be used to differentiate magnetic field orientations, which requires an external directional magnetic bias‐field. Our approach enables the measurement of magnetic field maps around magnetic structures with extensions on the micrometer scale.…”

“…[ 28 ] and Hatano et al. [ 29 ] report on using MNPs on top of diamond slabs with implanted NV center layers close to the surface to measure magnetic fields produced by MNPs while external magnetic fields are applied. By using applied external magnetic bias fields (B 0 ) to measure relative changes (∆B z ) in the magnetic field along the NV center axis (B z ) around MNPs following B z = B 0 + ∆B z , both these works reach magnetic field sensitivity in the order of μT and nanometer spatial resolution.…”

Towards a quantum interface between spin waves and paramagnetic spin baths

“…with the optical pumping rate, proportional to the pumping intensity (see Appendix B). These ensembles can reach NV center densities nv as high as nv ∼ 10 5 μm −3 [76,77,85,86] and even larger [87,88], although in such cases the extreme concentrations prove harmful for the coherence and decay times of NV centers. The shift β is shown in the left panel of Fig.…”

Towards a quantum interface between spin waves and paramagnetic spin baths

“…with Ω the optical pumping rate, proportional to the pumping intensity (see Appendix B). These ensembles can reach NV centre densities nv as high as nv ∼ 10 5 (µm) −3 [72,73,80,81] and even larger [82,83], although in such cases the extreme concentrations prove harmful for the coherence and decay times of NV centres. The shift Γ β is shown in the left panel of Fig.…”