Highly Sensitive Detection of Bio-magnetic Fields and Relevant Applications of Diamond Quantum Sensors
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-12-05 |
| Journal | The Brain & Neural Networks |
| Authors | Masaki Sekino |
| Institutions | The University of Tokyo |
| Analysis | Full AI Review Included |
Diamond Quantum Sensors for Highly Sensitive Biomagnetic Detection: A 6CCVD Technical Analysis
Section titled “Diamond Quantum Sensors for Highly Sensitive Biomagnetic Detection: A 6CCVD Technical Analysis”This document analyzes the research presented on Nitrogen-Vacancy (NV) diamond quantum sensors for highly sensitive biomagnetic field detection (MEG, MCG, Sentinel Lymph Node mapping) and outlines how 6CCVD’s advanced MPCVD diamond materials and fabrication services enable the replication and advancement of this critical technology.
Executive Summary
Section titled “Executive Summary”This paper confirms the critical role of diamond Nitrogen-Vacancy (NV) centers as next-generation quantum sensors for biomagnetic field measurement, offering significant advantages over traditional cryogen-dependent technologies like SQUID.
- Room Temperature Operation: NV diamond sensors function effectively at room temperature, eliminating the need for bulky, expensive cryogenic cooling required by SQUID systems, enabling compact and wearable devices.
- High Sensitivity & Dynamic Range: The technology achieves high sensitivity (target 10 pT Hz-1/2) and a wide dynamic range, crucial for detecting extremely weak biomagnetic signals (picoTesla to femtoTesla levels) in real-world, unshielded environments.
- Versatile Scale Integration: NV centers support sensing across a vast range of scales, from atomic-level resolution for cellular observation to millimeter-scale bulk diamond sensors suitable for Magnetoencephalography (MEG) and Magnetocardiography (MCG).
- Key Applications Validated: Successful application demonstrated in millimeter-scale rat MCG mapping and the development of compact magnetic probes for Sentinel Lymph Node (SLN) detection using magnetic nanoparticles (MNPs).
- Core Methodology: Optically Detected Magnetic Resonance (ODMR) is the primary readout technique, utilizing green laser excitation (532 nm) and red fluorescence detection (638-800 nm) to monitor Zeeman splitting induced by external magnetic fields.
- 6CCVD Material Requirement: Replication and scaling of this research require high-purity, low-strain Single Crystal Diamond (SCD) with precise, controlled nitrogen doping for optimal NV center formation and coherence.
Technical Specifications
Section titled “Technical Specifications”The following parameters highlight the performance requirements and operational characteristics of the NV diamond quantum sensors discussed in the research.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Excitation Wavelength | 532 | nm | Green laser source for ODMR initialization |
| NV Center Fluorescence Wavelength | 638-800 | nm | Red fluorescence signal used for magnetic readout |
| NV Center Ground State Transition | 2.87 | GHz | Zero-Field Splitting frequency (ODMR) |
| Target DC Sensitivity (Goal) | 10 | pT Hz-1/2 | Required sensitivity for biomagnetic field measurement (Ref 23) |
| Rat MCG Magnetic Field Detected | NanoTesla (nT) | nT | Measured field strength during millimeter-scale MCG mapping |
| Spatial Resolution Achieved (MCG) | Millimeter | mm | Achieved resolution for mapping cardiac current distribution |
| SLN Probe Size (Prototype) | 1 | cm | Compact size of the handheld magnetic probe (Figure 4b) |
| Diamond Operating Temperature | Room | °C | Key advantage over SQUID technology |
| SQUID Cryogen Requirement | Liquid He/N2 | N/A | Limitation of traditional high-sensitivity sensors |
Key Methodologies
Section titled “Key Methodologies”The research relies on the fundamental properties of the NV center in diamond, primarily utilizing Optically Detected Magnetic Resonance (ODMR) for magnetic field sensing.
- NV Center Initialization: The NV center (a nitrogen atom adjacent to a lattice vacancy) is initialized by irradiation with a 532 nm green laser, promoting the electron spin from the 3A2 ground state to the 3E excited state.
- Spin Readout (Fluorescence): The system relaxes back to the ground state, emitting red fluorescence (638-800 nm). The intensity of this fluorescence is spin-state dependent, allowing optical measurement of the spin state.
- Microwave Manipulation: Microwave radiation (near 2.87 GHz) is applied to drive transitions between the $m_s = 0$ and $m_s = \pm 1$ spin sublevels of the ground state.
- Zeeman Splitting Detection: An external magnetic field (B) causes Zeeman splitting of the $m_s = \pm 1$ sublevels. This splitting shifts the microwave resonance frequency.
- Magnetic Field Quantification: By monitoring the change in red fluorescence intensity (the ODMR spectrum) as a function of the microwave frequency, the magnitude of the external magnetic field (B) can be precisely determined.
- Application Specific Setup (MCG): For Magnetocardiography (MCG), a bulk polycrystalline diamond sensor was placed in close proximity (millimeter distance) to the heart of a rat, enabling high-resolution spatial mapping of cardiac current sources.
- Application Specific Setup (SLN Probe): For Sentinel Lymph Node (SLN) detection, a compact magnetic probe was developed, integrating a solenoid coil (to magnetize MNPs) and a small diamond quantum sensor for localized detection of the resulting magnetic field.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the high-specification MPCVD diamond materials and custom fabrication services required to replicate and advance the quantum sensing research detailed in this paper.
Applicable Materials for Quantum Sensing
Section titled “Applicable Materials for Quantum Sensing”To achieve the high sensitivity (10 pT Hz-1/2) and long coherence times necessary for biomagnetic detection, the highest quality Single Crystal Diamond (SCD) is essential.
| Material Specification | 6CCVD Offering | Relevance to Research |
|---|---|---|
| Optical Grade SCD | High-purity, low-strain SCD wafers. | Required for maximizing NV center coherence time (T2) and minimizing background noise. |
| Controlled N-Doping | Custom nitrogen incorporation during growth. | Essential for precise control over NV center density, balancing sensitivity (high density) and coherence (low density). |
| Substrate Thickness | SCD plates from 0.1 µm up to 500 µm. | Allows researchers to select optimal thickness for either bulk sensing (millimeter scale MCG) or thin-film integration (nanocavity structures, Ref 24). |
| Polycrystalline Diamond (PCD) | High-quality PCD wafers up to 125 mm diameter. | Suitable for large-area imaging applications or where bulk material is preferred for mechanical stability. |
Customization Potential for Advanced Sensor Integration
Section titled “Customization Potential for Advanced Sensor Integration”The development of compact, integrated quantum magnetometers (like the SLN probe or wearable MEG systems) requires precise material engineering beyond standard wafer supply.
- Custom Dimensions and Shaping: 6CCVD offers laser cutting and shaping services to produce the small, custom-sized diamond elements required for compact probes (e.g., the 1 cm prototype shown in Figure 4b) or for integration into microwave delivery structures.
- Ultra-Low Roughness Polishing: Quantum sensing performance is highly dependent on surface quality. 6CCVD guarantees Ra < 1 nm polishing for SCD, minimizing surface defects that degrade NV center coherence and optical coupling efficiency.
- Integrated Metalization Services: The ODMR technique requires efficient microwave delivery (e.g., coplanar waveguides) and electrical contacts. 6CCVD provides in-house custom metalization using materials critical for microwave circuits, including:
- Ti/Pt/Au stacks for robust, low-loss contacts.
- W and Cu for specialized thermal or electrical requirements.
Engineering Support and Global Logistics
Section titled “Engineering Support and Global Logistics”6CCVD’s in-house PhD team specializes in MPCVD diamond growth and material science, offering direct consultation to optimize material selection for specific quantum sensing projects.
- Application Expertise: Our team can assist researchers in selecting the optimal SCD grade and nitrogen concentration required to replicate or extend the Highly Sensitive Biomagnetic Detection projects described in this paper (MEG, MCG, SLN detection).
- Global Supply Chain: We ensure reliable, global delivery of custom diamond wafers, offering both DDU (Delivered Duty Unpaid) default and DDP (Delivered Duty Paid) options to streamline international research procurement.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
本稿では，生体磁気計測のための次世代型量子センサとして期待されているダイヤモンド窒素—空孔中心について，計測技術の現状と今後の応用可能性について述べる．心臓の電気活動に由来する微弱な磁場のマッピングから心臓内の電流分布を推定して機能的評価を行う心磁図や，同様に脳の機能的評価を行う脳磁図は，基礎研究から臨床の検査まで幅広い応用を有している．これらを中心とする超高感度の生体磁気計測には，超伝導量子干渉計が長く用いられてきたが，冷媒が必要なため普及に課題があった．近年，冷媒を必要としない超高感度磁気センサが急速に発達しており，中でもダイヤモンド窒素—空孔中心は，究極的には原子レベルの高分解能を有し，固体であることから集積化に向いており，ダイナミックレンジが高くリアルワールドでの応用に適するなどの特徴から，注目を集めている．生体計測の具体的事例として，動物の心磁図の計測や，リンパ節へ取り込まれた微量の磁性ナノ粒子の検出などが報告されている．機器のコンパクト性を活かして，今後は自動車のドライバーの脳機能計測や遠隔医療など，応用の開拓が期待されている．