Nanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamonds
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-06 |
| Journal | ACS Nano |
| Authors | Jan BartoĆ, Michal Gulka, JĂĄn TarĂĄbek, Yuliya Mindarava, Zhenyu Wang |
| Institutions | Center for Integrated Quantum Science and Technology, Charles University |
| Citations | 108 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Nanoscale Dynamic Redox Readout using NV Centers
Section titled âTechnical Documentation & Analysis: Nanoscale Dynamic Redox Readout using NV CentersâThis document analyzes the research paper âNanoscale Dynamic Readout of a Chemical Redox Process Using Radicals Coupled with Nitrogen-Vacancy Centers in Nanodiamondsâ to extract critical technical specifications and align them with the advanced MPCVD diamond solutions offered by 6CCVD.
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a highly sensitive, nanoscale quantum sensing tool capable of dynamically monitoring chemical redox reactions using Nitrogen-Vacancy (NV) centers in nanodiamonds (NDs).
- Core Breakthrough: Achieved ultra-sensitive detection of paramagnetic species (nitroxide radicals) by magnetically coupling them to NV centers in a polymer shell.
- Ultimate Sensitivity: Demonstrated detection down to ~10 single radical spins per ND particle, corresponding to a localized readout of approximately $10^{-23}$ mol.
- Sensing Mechanism: The $T_1$ longitudinal spin relaxation time of the NV center is shortened significantly upon interaction with the fluctuating magnetic field generated by the radicals.
- Methodology: Utilized all-optical, Microwave (MW)-free $T_1$ relaxometry at the single-particle level, enabling dynamic monitoring of the reduction of nitroxide radicals by ascorbic acid (Vitamin C) in an aqueous, ambient environment.
- Material Requirement: The success relies on high-quality fluorescent nanodiamonds with controlled NV concentration (one to few NV centers per particle) and precise surface functionalization (poly(glycerol) shell).
- 6CCVD Value Proposition: 6CCVD provides the high-purity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) substrates necessary for developing next-generation, scalable quantum sensors with superior control over NV depth, concentration, and surface quality compared to conventional nanodiamond powders.
Technical Specifications
Section titled âTechnical SpecificationsâThe following critical parameters were extracted from the experimental results and characterization data:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sensing Mechanism | $T_1$ Longitudinal Spin Relaxation | ”s | Optically detected, MW-free relaxometry |
| Ultimate Spin Sensitivity | ~10 | spins per ND particle | Limit for nitroxide radical detection |
| Molar Sensitivity (Localized) | $\approx 10^{-23}$ | mol | Achieved in the localized detection volume |
| $T_1$ Time (Max Radical Load ND5) | 22.0 | ”s | 134 stable nitroxide radicals/particle |
| $T_1$ Time (Min Radical Load ND1) | 99.0 | ”s | 0 stable nitroxide radicals detected |
| Polymer Layer Thickness (Native) | $17.0 \pm 8.8$ | nm | Poly(glycerol) shell thickness (Cryo-TEM) |
| ND Core Size (Precursor) | 0-50 | nm | Commercial HPHT Nanodiamonds (MSY 0-0.05 ”m) |
| NV Center Concentration | 1 to few | NV centers per particle | Estimated concentration in ND0 |
| NV Creation Method | 16.6 MeV Electron Beam Irradiation | $1.25 \times 10^{19}$ particles cm-2 | Followed by $900$ °C annealing |
| Dynamic Readout Resolution | 1-2 | minutes | Acquisition time per single ND site |
Key Methodologies
Section titled âKey MethodologiesâThe experimental procedure involved precise material synthesis and advanced quantum optical measurement techniques:
- ND Precursor Preparation: HPHT nanodiamonds (NDs) were oxidized, treated with acids/bases, and purified.
- NV Center Creation: NDs were subjected to high-energy 16.6 MeV electron beam irradiation followed by high-temperature annealing at 900 °C for 1 hour to create fluorescent NV centers.
- Surface Functionalization (ND0-PG): The NDs were coated with a hyperbranched poly(glycerol) layer terminated with alkyne functional groups to ensure colloidal stability and provide anchoring sites.
- Radical Attachment (ND1-5): TEMPO-based nitroxide radicals were covalently attached to the polymer shell using Cu(I)-catalyzed azide-alkyne cycloaddition (âclick chemistryâ).
- Radical Quantification: Bulk Electron Paramagnetic Resonance (EPR) spectroscopy was used to quantify the absolute number of radicals attached (up to 134 radicals/particle for ND5).
- Quantum Sensing: Confocal microscopy was used to perform all-optical $T_1$ spin relaxometry on single ND particles in an aqueous environment.
- Dynamic Redox Monitoring: The $T_1$ time recovery was monitored in real-time (minute resolution) after the addition of ascorbic acid, demonstrating the dynamic readout capability of the nanosensor.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe groundbreaking work in nanoscale quantum sensing requires diamond materials with exceptional purity, precise defect engineering, and robust surface control. 6CCVD is uniquely positioned to supply the next generation of diamond platforms needed to advance and scale this research from nanodiamond powders to integrated solid-state devices.
Applicable Materials for Quantum Sensing Platforms
Section titled âApplicable Materials for Quantum Sensing PlatformsâTo replicate or extend this research onto more stable, scalable platforms (e.g., thin films or bulk substrates), 6CCVD recommends the following materials:
| 6CCVD Material | Recommended Grade | Application Relevance |
|---|---|---|
| Single Crystal Diamond (SCD) | Optical Grade SCD | Ideal for high-coherence quantum sensing platforms requiring low intrinsic noise and high purity. Essential for controlled NV creation via ion implantation (not used here, but superior for thin films). |
| Polycrystalline Diamond (PCD) | High-Purity PCD | Suitable for large-area sensing arrays (up to 125mm wafers) where high NV density ensembles are required for bulk sensing or scaling up the $T_1$ relaxometry technique. |
| Boron-Doped Diamond (BDD) | Heavy Boron Doped PCD | Relevant for electrochemical sensing extensions, where the BDD surface conductivity could be integrated with the NV sensing layer for combined redox/electrical readout. |
Customization Potential for Advanced NV Research
Section titled âCustomization Potential for Advanced NV ResearchâThe paper highlights the critical role of NV center concentration, depth, and surface quality in determining $T_1$ relaxation time and overall sensitivity. 6CCVD offers precise control over these parameters, enabling researchers to move beyond polydisperse nanodiamonds:
- Controlled NV Creation: While the paper used electron irradiation, 6CCVD provides high-purity SCD substrates optimized for subsequent ion implantation (e.g., Nitrogen or Silicon) to achieve precise, shallow NV layers (sub-10 nm depth control), which is crucial for maximizing coupling to surface-bound radicals.
- Surface Preparation: We offer ultra-low roughness polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD) to minimize surface noise ($T_{1}^{\text{noise}}$), thereby enhancing the signal contrast derived from the external radical spins.
- Custom Dimensions: For scaling up sensor prototypes, 6CCVD supplies plates and wafers up to 125mm (PCD), allowing for the fabrication of large-scale integrated quantum sensor arrays.
- Metalization Services: Although the paper focused on polymer coating, 6CCVD offers custom metalization (Au, Pt, Ti, Pd, W, Cu) for integrating diamond sensors into microfluidic or electronic readout systems, facilitating complex chemical transducer architectures.
Engineering Support
Section titled âEngineering SupportâThe successful implementation of $T_1$ relaxometry for dynamic redox monitoring depends heavily on optimizing the diamond material properties.
- NV Optimization: 6CCVDâs in-house PhD team specializes in optimizing diamond growth and post-processing (irradiation and annealing protocols) to achieve the desired NV density and coherence properties required for high-sensitivity chemical redox sensing projects.
- Material Selection: We provide consultation on selecting the optimal diamond type (SCD vs. PCD) and thickness (from 0.1 ”m thin films up to 10 mm substrates) to balance quantum coherence, optical access, and mechanical stability for specific biological or chemical environments.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive diamond materials directly to your research facility.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Biocompatible nanoscale probes for sensitive detection of paramagnetic species and molecules associated with their (bio)chemical transformations would provide a desirable tool for a better understanding of cellular redox processes. Here, we describe an analytical tool based on quantum sensing techniques. We magnetically coupled negatively charged nitrogen-vacancy (NV) centers in nanodiamonds (NDs) with nitroxide radicals present in a bioinert polymer coating of the NDs. We demonstrated that the T1 spin relaxation time of NV centers is very sensitive to the number of nitroxide radicals, with a resolution down to ~10 spins per ND (detection of approximately 10-23 mol in a localized volume). The detection is based on T1 shortening upon the radical attachment and we propose a theoretical model describing this phenomenon. We further show this colloidally stable, water-soluble system can be used dynamically for spatiotemporal readout of a redox chemical process (oxidation of ascorbic acid) occurring near the ND surface in an aqueous environment under ambient conditions.