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6CCVD Research

Advanced post-treatment strategy for quantum-grade fluorescent nanodiamonds

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-09-25
JournalFrontiers in Quantum Science and Technology
AuthorsMasfer Alkahtani, Yahya Alzahrani, Ayla Hazrathosseini, Abdulmalik M. Alessa, Maabur Sow
AnalysisFull AI Review Included

Advanced Post-Treatment Strategy for Quantum-Grade Fluorescent Nanodiamonds

Section titled “Advanced Post-Treatment Strategy for Quantum-Grade Fluorescent Nanodiamonds”

Executive Summary

Section titled “Executive Summary”
  • Novel Purification Protocol: A multi-step KAA (KNO3-Acid-Alkaline) purification strategy was developed, integrating molten potassium nitrate (KNO3) oxidative etching with sequential wet-chemical cleaning (H2SO4/HNO3, NaOH, HCl).
  • Enhanced Spin Coherence: The protocol achieved an extended average spin-lattice relaxation time (T1) of 2045 ”s, nearly doubling the performance of untreated FNDs (1045 ”s).
  • High Quantum Readout Fidelity: The Optically Detected Magnetic Resonance (ODMR) contrast was significantly boosted to 11.5%, confirming stable NV charge environments and effective impurity removal.
  • Colloidal Stability: KAA-FNDs demonstrated excellent long-term colloidal stability, achieving a monodisperse hydrodynamic size of 100 nm and a strong negative zeta potential of -30 mV.
  • Impurity Mitigation: The combined approach effectively eliminates surface sp2 carbon, paramagnetic defects, and residual ionic contaminants (e.g., potassium and nitrate salts), which typically quench NV fluorescence and accelerate spin decoherence.
  • Scalability and Yield: The method is chemically rational, reproducible, and scalable, preserving the bulk material with a high recovery yield of approximately 96%.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Starting Material Size100nmHPHT FNDs (mean particle size)
KNO3 Etching Temperature580°CThermal oxidation step
KNO3 Etching Duration10minThermal oxidation step
Acid Oxidation Temperature75°CH2SO4/HNO3 (9:1 v/v) treatment
Acid Oxidation Duration72hH2SO4/HNO3 (9:1 v/v) treatment
KAA-FND T1 Relaxation Time2045”sAverage spin-lattice relaxation time (NV centers)
Untreated FND T1 Relaxation Time1045”sBaseline performance
KAA-FND ODMR Contrast11.5%Optically Detected Magnetic Resonance
Untreated FND ODMR Contrast3%Baseline performance
KAA-FND Hydrodynamic Size100nmDynamic Light Scattering (DLS)
KAA-FND Zeta Potential-30mVElectrostatic stability (highly stable colloid)
Material Recovery Yield96%Mass recovered after full KAA protocol

Key Methodologies

Section titled “Key Methodologies”

The KAA (KNO3-Acid-Alkaline) protocol involves two main stages designed for synergistic purification:

  1. Molten KNO3 Oxidative Etching (Step 1):

    • FNDs mixed with KNO3 (2 mg FNDs per 1 g KNO3).
    • Heated in a ceramic crucible at 580 °C for 10 minutes.
    • Purpose: Rapidly etches surface-bound sp2 carbon, removes disordered carbon, and induces morphological reshaping (from irregular to rounded/faceted).

  2. Sequential Wet-Chemical Cleaning (Step 2):

    • Acid Oxidation (Step 2.1):
      • Treated FNDs immersed in concentrated H2SO4/HNO3 (9:1 v/v).
      • Stirred continuously at 75 °C for 72 hours.
      • Purpose: Aggressively removes residual graphite and amorphous carbon, and grafts hydrophilic groups (-COOH, -OH) onto the surface.
    • Alkaline Wash (Step 2.2):
      • Resuspended in 0.1 M NaOH solution, heated at 90 °C for 2 hours.
      • Purpose: Neutralizes residual acids, converts -COOH groups to soluble -COO- carboxylates, dissolves remaining metal ions (including potassium), and enhances negative surface charge/solubility.
    • Final Acid Wash (Step 2.3):
      • Treated with 0.1 M HCl at 90 °C for 2 hours.
      • Purpose: Removes residual alkali or transition metal contaminants (e.g., Fe2+, Cu2+) by converting them into soluble chlorides, ensuring a clean, electronically quiet NV environment.

Commercial Applications

Section titled “Commercial Applications”

The production of high-purity, quantum-grade FNDs with enhanced spin coherence and colloidal stability is critical for several advanced technological sectors:

  • Quantum Sensing and Metrology:
    • Nanoscale Magnetometry: High T1 and ODMR contrast enable high-fidelity detection of local magnetic fields, crucial for probing spin dynamics in materials and biological systems.
    • Nanoscale Thermometry: FNDs are used for high-precision temperature sensing in ambient and biological environments.
  • Biophotonics and Bioimaging:
    • Super-resolution Bioimaging: Stable, bright, and non-toxic FNDs are ideal for tracking biological processes in living cells.
    • Drug Delivery: Excellent biocompatibility and colloidal stability allow FNDs to be used as carriers in fluid-phase delivery systems.
  • Nanophotonics and Spintronics:
    • On-Chip Device Engineering: FNDs serve as robust, optically active components for integrating quantum emitters into photonic and spintronic circuits.
  • Materials Science:
    • Nanocomposite Development: High purity and uniform morphology make FNDs suitable fillers for composites requiring exceptional hardness or thermal conductivity.
View Original Abstract

Fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV − ) centers are promising platforms for quantum sensing and bioimaging, but their performance is often limited by surface defects, residual graphitic carbon, and ionic contamination. Here, we report a multistep surface treatment strategy combining molten potassium nitrate (KNO 3 ) thermal oxidation with sequential acid and alkaline cleaning to produce high-quality, quantum-grade FNDs. Molten KNO 3 etching at 580 °C enables morphological reshaping and partial oxidation, while subsequent H 2 SO 4 /HNO 3 , NaOH, and HCl washes eliminate graphitic residues, neutralize surface charges, and remove metal ions. This protocol yields discrete, colloidally stable FNDs with enhanced photoluminescence, a high ODMR contrast of 11.5%, and extended average spin-lattice relaxation time (T 1 ≈ 2045 ”s). Dynamic light scattering and ζ-potential measurements confirm excellent dispersion (∌100 nm, −30 mV). The integration of chemical, morphological, and spin-performance improvements establishes a scalable route for producing FNDs suitable for high-fidelity quantum sensing and biophotonic applications.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2014 - Diamond nanophotonics [Crossref]
  2. 2023 - Silicon vacancy in boron-doped nanodiamonds for optical temperature sensing [Crossref]
  3. 2017 - Nanometer-scale luminescent thermometry in bovine embryos [Crossref]
  4. **** - Tin-vacancy in diamonds for luminescent thermometry [Crossref]
  5. **** - Fluorescent nanodiamonds: past, present, and future [Crossref]
  6. **** - Fluorescent nanodiamonds for luminescent thermometry in the biological transparency window [Crossref]
  7. 2023 - Engineering sub-10 nm fluorescent nanodiamonds for quantum enhanced biosensing [Crossref]
  8. 2020 - Nanoscale dynamic readout of a chemical redox process using radicals coupled with nitrogen-vacancy centers in nanodiamonds [Crossref]
  9. 2009 - High yield fabrication of fluorescent nanodiamonds [Crossref]
  10. 2018 - Effect of structure and composition of nanodiamond powders on thermal stability and oxidation kinetics [Crossref]

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