| Metadata | Details |
|---|
| Publication Date | 2020-10-19 |
| Journal | Frontiers in Physics |
| Authors | James L. Webb, Luca Troise, Nikolaj Winther Hansen, Jocelyn Achard, Ovidiu Brinza |
| Institutions | Centre National de la Recherche Scientifique, Technical University of Denmark |
| Citations | 38 |
| Analysis | Full AI Review Included |
- Core Achievement: Demonstrated a diamond Nitrogen Vacancy (NV) center magnetometer setup achieving a DC/low frequency magnetic field sensitivity of ~100 pT/âHz, optimized for biological measurements.
- Material Basis: High-quality, 20 ”m 12C purified CVD diamond layer (5 ppm 14N) was used, yielding a narrow ODMR linewidth (FWHM ~1 MHz) essential for high sensitivity.
- Setup Optimization: The system utilizes an inverted microscope geometry with 532 nm laser illumination coupled at Brewsterâs angle to maximize fluorescence output (up to 6 mW) and minimize laser leakage into the sample.
- Noise Mitigation: Technical noise (laser fluctuations) was rejected using balanced photodetectors, and strong ambient magnetic noise (50/150 Hz mains) was effectively removed using adaptive FFT-based phase drift correlation and subtraction, eliminating the need for bulky shielding.
- Biocompatibility: Thermal management was addressed using Aluminum Nitride (AlN) plates and thin Kapton/Al foil insulation to dissipate heat from the 2 W pump laser while maintaining the biological sample (mouse brain slice) at viable temperatures (35-37°C).
- Pulsed Sensing: Measured the ensemble readout time for pulsed magnetometry to be approximately 1 ms, which can be reduced to 200-300 ”s at high laser intensity (1.5 kW/cm2).
- Imaging Limitations: Identified and characterized systematic artifacts in widefield imaging (e.g., MW field inhomogeneity, vibration wobble) that can falsely resemble magnetic field patterns, limiting current imaging sensitivity to ~50 nT/âHz per pixel.
| Parameter | Value | Unit | Context |
|---|
| DC/Low Frequency Sensitivity | ~100 | pT/âHz | Achieved bulk magnetometry sensitivity. |
| Theoretical Shot Noise Limit | 10-20 | pT/âHz | Estimated maximum sensitivity for DC/low frequency. |
| Widefield Imaging Sensitivity (Est.) | ~50 | nT/âHz | Estimated per pixel sensitivity (shot noise limited). |
| NV Layer Thickness | 20 | ”m | CVD-grown 12C purified layer. |
| Nitrogen Doping Concentration | 5 | ppm | 14N concentration in the CVD layer. |
| Annealing Temperature | 800 | °C | Post-irradiation thermal treatment. |
| ODMR Linewidth (FWHM) | ~1 | MHz | Measured on the high-quality diamond sample. |
| Maximum ODMR Contrast | 5.1 | % | Achieved at maximum field sensitivity point. |
| Pump Laser Wavelength | 532 | nm | DPSS laser source. |
| Maximum Pump Power | 2 | W | Used for bulk magnetometry. |
| Fluorescence Output (Max) | 5-6 | mW | Collected from the diamond at 2 W pump power. |
| DC Offset Magnetic Field | ~1.6 | mT | Used to Zeeman split the ms = ±1 states. |
| Ensemble Readout Time (Decay) | ~1 | ms | Typical decay time; reduced to 200-300 ”s at 218 mW laser power. |
| Laser Intensity (Pulsed Readout) | 1.5 | kW/cm2 | Estimated intensity at the diamond surface during high-power readout. |
| Biological Sample Temperature | 35-37 | °C | Optimal range maintained using thermal management. |
| MW Frequency Modulation | 33 | kHz | Modulation frequency used for CW ODMR detection. |
- Diamond Material Engineering: Used a 12C isotopically purified CVD diamond layer (20 ”m thick, 5 ppm 14N doping) to minimize 13C spin bath effects, followed by H+ irradiation and 800°C annealing to maximize NV density while maintaining narrow linewidth.
- Optical Excitation: Implemented Brewsterâs angle illumination (67.5°) using a tilted mirror and half-wave plate to maximize 532 nm pump light coupling into the diamond and increase internal reflection, boosting fluorescence generation.
- Thermal Management and Sample Interface: Utilized an Aluminum Nitride (AlN) plate as a thermally conductive, electrically insulating heatsink, with the diamond placed in a laser-cut hole. Thin Kapton tape and aluminum foil were used as insulation layers between the diamond and the biological sample to minimize heat transfer while maintaining close proximity.
- Magnetic Noise Cancellation (Software-Based): Employed Fast Fourier Transform (FFT) post-processing, including correlation with a reference mains signal, to track and subtract phase drift and amplitude fluctuations of 50/150 Hz ambient magnetic noise, achieving effective filtering without physical shielding.
- CW Magnetometry: Performed continuous wave (CW) ODMR sensing using a broadband PCB antenna and a three-frequency drive method, detecting the fluorescence change via a balanced photodetector and lock-in amplifier at the maximum slope point of the resonance curve.
- Pulsed Magnetometry: Used a TTL pulse generator (Spincore Pulseblaster) and fast switches (RF/AOM) to generate initialization and readout pulses, measuring the ensemble reinitialization time to assess bandwidth limitations for DC sensing.
- Biocompatible Setup: Designed a custom 3D-printed bath chamber for biological samples, allowing constant flow of carbogenated solution (5% CO2, 95% O2) via a peristaltic pump to maintain tissue viability for extended averaging periods (thousands of stimulations).
- Non-Cryogenic Biomagnetometry: Provides a solid-state alternative to SQUID systems for Magnetoencephalography (MEG) and Magnetocardiography (MCG), eliminating the need for expensive cryogenic cooling and magnetically shielded rooms.
- High-Resolution Biosensing: Enables high spatial resolution (micrometer scale) imaging of magnetic fields generated by biological currents (e.g., neural activity) in tissue slices, a capability difficult to achieve with competing techniques.
- Quantum Material Manufacturing: Requires and drives the development of high-purity, isotopically enriched (12C) CVD diamond substrates with controlled nitrogen doping and precise defect creation (irradiation/annealing).
- Advanced Microscopy Systems: Applicable in specialized inverted microscopy setups requiring high-power laser delivery, efficient fluorescence collection (using objectives/condenser lenses), and integration of fast RF/optical switching for pulsed quantum measurements.
- Thermal Management Solutions: The use of AlN plates as electrically insulating, thermally conductive heatsinks is relevant for any high-power solid-state quantum device where heat dissipation near sensitive components is critical.
View Original Abstract
Sensing of signals from biological processes, such as action potential propagation\nin nerves, are essential for clinical diagnosis and basic understanding of physiology.\nSensing can be performed electrically by placing sensor probes near or inside a\nliving specimen or dissected tissue using well-established electrophysiology techniques.\nHowever, these electrical probe techniques have poor spatial resolution and cannot easily\naccess tissue deep within a living subject, in particular within the brain. An alternative\napproach is to detect the magnetic field induced by the passage of the electrical signal,\ngiving the equivalent readout without direct electrical contact. Such measurements are\nperformed today using bulky and expensive superconducting sensors with poor spatial\nresolution. An alternative is to use nitrogen vacancy (NV) centers in diamond that promise\nbiocompatibilty and high sensitivity without cryogenic cooling. In this work we present\nadvances in biomagnetometry using NV centers, demonstrating magnetic field sensitivity\nof âŒ100 pT/âHz in the DC/low frequency range using a setup designed for biological\nmeasurements. Biocompatibility of the setup with a living sample (mouse brain slice)\nis studied and optimized, and we show work toward sensitivity improvements using a\npulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic\nartifacts in NV-ensemble widefield fluorescence imaging are investigated.
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- 2020 - Miniaturized magnetic sensors for implantable magnetomyography [Crossref]
- 2018 - Moving magnetoencephalography towards real-world applications with a wearable system [Crossref]
- 2008 - High-sensitivity diamond magnetometer with nanoscale resolution [Crossref]
- 2011 - Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells [Crossref]
- 2010 - Optical properties of the nitrogen-vacancy singlet levels in diamond [Crossref]
- 2014 - Magnetometry with nitrogen-vacancy defects in diamond [Crossref]
- 2014 - Nitrogen-vacancy centers in diamond: nanoscale sensors for physics and biology [Crossref]
- 2020 - Sensitivity optimization for NV-diamond magnetometry [Crossref]