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Quantum sensing of paramagnetic analytes by nanodiamonds in levitated microdroplets and aqueous solutions

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-01-01
JournalChemical Science
AuthorsEmily K. Brown, Zachary R. Jones, Adrisha Sarkar, Brandon J. Wallace, Ashok Ajoy
InstitutionsLawrence Berkeley National Laboratory, University of California, Berkeley
AnalysisFull AI Review Included

Technical Documentation: Quantum Sensing with MPCVD Diamond

Section titled “Technical Documentation: Quantum Sensing with MPCVD Diamond”

Executive Summary

Section titled “Executive Summary”

This documentation analyzes a study demonstrating the quantitative quantum sensing of paramagnetic analytes (Gd+3) using Nitrogen-Vacancy (NV) centers in nanodiamonds (ND-NV-) within complex aqueous and microdroplet environments. The findings underscore the critical role of precise material engineering—specifically diamond size, shape, and surface chemistry—for reproducible quantum sensor performance.

  • Validated Quantum Sensing Modality: Confirmed ND-NV- as a robust, room-temperature quantum sensor for paramagnetic species (Gd+3) in picoliter volumes (microdroplets).
  • Adsorption-Driven Detection: Established that the Optically Detected Magnetic Resonance (ODMR) response is non-linear and governed by the thermodynamic adsorption of Gd+3 to the diamond surface, modeled accurately by a Langmuir isotherm.
  • Critical Material Parameters: Demonstrated that ODMR sensitivity is strongly dependent on pH (controlling surface charge), ND size (70 nm particles showed highest sensitivity), and particle shape (non-spherical/ellipsoidal geometry is required for accurate modeling).
  • Thermodynamic Constant: Determined the equilibrium constant (Keq) for Gd+3 adsorption to carboxylated ND surfaces to be (1 ± 0.5) x 105 M-1, corresponding to a thermodynamically favorable free energy of adsorption (ΔG°) of (-28 ± 1) kJ mol-1.
  • Microenvironment Effects: Observed a significant shift in sensing sensitivity between bulk solutions and microdroplets due to solution phase depletion of Gd+3 caused by the high surface-area-to-volume ratio of NDs in small compartments.
  • 6CCVD Value Proposition: 6CCVD provides the high-purity Single Crystal Diamond (SCD) precursors necessary for manufacturing next-generation ND-NV- sensors with controlled NV density, precise surface termination, and customized geometries required to replicate and advance this quantitative sensing research.

Technical Specifications

Section titled “Technical Specifications”

The following hard data points were extracted from the experimental results and theoretical modeling:

ParameterValueUnitContext
NV Center Concentration~3ppmNanodiamonds used in experiments
ODMR Transition Frequency2.865GHzMicrowave frequency for ms = 0 to ms = ±1 transition
Laser Excitation Wavelength532nmOptical excitation source
Laser Power (Droplet Measurement)0.5WSpot size ~1 mm2
Microwave Power (Transmitted)~6WAverage power delivered to antenna
Nanodiamond Nominal Diameters70, 100, 140, 750nmHydrodynamic diameter (DLS)
Microdroplet Radius (Average)17”mLevitated in quadrupole trap
Relative Humidity (Trap)80 ± 3.5%Maintained stability for droplet experiments
Gd+3 Concentration Range (Bulk)10 nM to 1.5mMTested range for ODMR response
Gd+3 Adsorption Equilibrium Constant (Keq)(1 ± 0.5) x 105M-1Adsorption to carboxylated ND surface
Free Energy of Adsorption (ΔG°)-28 ± 1kJ mol-1Thermodynamically favorable adsorption
Optimal ND Size Sensitivity70nmExhibited largest ODMR response (72% saturation)
NV Exclusion Depth6nmAssumed depth of NV0 state near surface

Key Methodologies

Section titled “Key Methodologies”

The quantitative quantum sensing was achieved through precise control of the diamond material and the microenvironment:

  1. Material Selection: Carboxylated (-COOH) red fluorescent nanodiamonds (ND) with nominal hydrodynamic diameters ranging from 70 nm to 750 nm and an NV concentration of approximately 3 ppm were utilized.
  2. Microdroplet Setup: Individual droplets (average radius 17 ”m) were charged and levitated in a branched quadrupole trap maintained at 80 ± 3.5% relative humidity (using a 55% water/45% glycerol solvent mixture).
  3. ODMR Measurement: Optically Detected Magnetic Resonance (ODMR) spectra were acquired by exciting the NV centers with a 532 nm laser and applying modulated microwave irradiation (2.825 to 2.925 GHz) via an antenna inserted into the trap.
  4. Self-Referential Collision Scheme: Two oppositely charged droplets (one containing NDs, one containing Gd+3) were collided to enable self-referential ODMR measurement, quantifying the change in contrast upon analyte addition.
  5. Quantitative Modeling: A photophysical model was developed, embedding a Langmuir adsorption isotherm to link the bulk concentration of Gd+3 to the surface spin density (σ) detected by the NV centers.
  6. Shape Correction: The ND shape was modeled as an ellipsoid (aspect ratio ~3) rather than a sphere to accurately account for the short-range (nanometer scale) interaction between the adsorbed Gd+3 and the internal NV centers, confirming the importance of particle geometry.
  7. Environmental Analysis: Experiments were conducted across a range of pH values (2.5 to 11) and in the presence of competitive ions (ZnCl2) and ligands (Zn-acetate) to quantify their impact on Gd+3 adsorption and subsequent ODMR response.

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

This research highlights the necessity of highly controlled, customized diamond materials for advancing quantitative quantum sensing. 6CCVD, as an expert supplier of MPCVD diamond, is uniquely positioned to meet the stringent material requirements for replicating and extending this work into commercial applications.

Research Requirement6CCVD Material Solution & CapabilityValue Proposition for Engineers/Scientists
High-Purity NV Precursors (3 ppm NV density, controlled depth)Single Crystal Diamond (SCD) Wafers: We supply ultra-low defect, high-purity SCD plates (up to 500 ”m thick) grown via MPCVD. This material is the ideal foundation for precise NV center creation via ion implantation and annealing, ensuring reproducible sensor performance.Guaranteed Foundation: Start your quantum sensing project with the highest quality, lowest strain SCD, maximizing NV coherence time (T2) and yield.
Custom Geometries & Shape Control (Ellipsoidal/disk-like shape critical for accurate modeling)Custom Dimensions & Polishing: We provide SCD and PCD plates up to 125mm in diameter. Our advanced laser cutting and polishing services (Ra < 1nm for SCD, < 5nm for PCD) enable the creation of custom substrates or precursor materials optimized for subsequent controlled milling into NDs of specific, non-spherical geometries.Tailored Dimensions: Receive diamond plates cut and polished to exact specifications, facilitating integration into microfluidic or Lab-on-a-Chip systems.
Microfluidic Integration & Substrates (Need for thin films and integrated components)Thin Film SCD/PCD: We offer thin diamond films down to 0.1 ”m thickness, ideal for minimizing optical path length and maximizing signal collection when integrating sensors into microfluidic channels or microdroplet traps.Seamless Integration: Utilize thin, robust diamond films that maintain superior thermal and optical properties for complex micro-scale experiments.
Surface Functionalization & Integration (Need for carboxylated surfaces, metal contacts)Custom Metalization Services: 6CCVD offers in-house metal deposition (Au, Pt, Pd, Ti, W, Cu) for creating precise electrical contacts or surface functionalization layers necessary for controlling analyte adsorption kinetics (Keq) in sensing devices.Integrated Sensor Platforms: Simplify your fabrication process by receiving diamond materials pre-metalized and ready for bonding or electrochemical functionalization.
Quantitative Sensing Support (Need to correlate material properties with photophysical models)Expert Engineering Support: Our in-house PhD team specializes in diamond material science and quantum defect engineering. We provide consultation on optimizing NV density, depth, and surface termination to match the requirements of advanced quantitative models like the Langmuir adsorption framework used in this study.Accelerated R&D: Leverage 6CCVD’s expertise to select the optimal diamond specifications, reducing development time and ensuring material consistency for high-precision chemical sensing.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The role of the aqueous phase environment ( e.g. , pH and salt concentration) on the adsorption of gadolinium to the surface of nanodiamonds with nitrogen-vacancy (NV − ) centers is investigated in microdroplets and in bulk solution.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2023 - arXiv [Crossref]

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