Engineering sub-10 nm fluorescent nanodiamonds for quantum enhanced biosensing

At a Glance

Metadata	Details
Publication Date	2023-06-02
Journal	Frontiers in Quantum Science and Technology
Authors	Masfer Alkahtani, Yahya A. Alzahrani, Philip Hemmer
Institutions	Texas A&M University, King Abdulaziz City for Science and Technology
Citations	4
Analysis	Full AI Review Included

Technical Analysis: Engineering Sub-10 nm Fluorescent Nanodiamonds for Quantum Enhanced Biosensing

This document analyzes the research concerning the synthesis and characterization of high-quality, sub-10 nm fluorescent nanodiamonds (FNDs) for advanced quantum sensing applications, specifically focusing on the Nitrogen-Vacancy (NV) and Silicon-Vacancy (SiV) color centers. The findings are mapped directly to 6CCVD’s capabilities in MPCVD diamond growth, custom doping, and advanced material processing.

Executive Summary

Core Challenge Addressed: The research focuses on overcoming the performance limitations of small FNDs (< 10 nm) by engineering growth methods (HPHT and LPLT) to achieve color center properties comparable to bulk diamond.
Methodology Validation: Diamond growth was rigorously validated not just by structural analysis (Raman, TEM) but critically by the successful creation and characterization of magnetically sensitive NV and SiV color centers.
Key Achievement (NV Quality): Optimized growth conditions resulted in NV centers exhibiting stable negative charge (NV^-) and low P1 nitrogen content, evidenced by a narrow Optically Detected Magnetic Resonance (ODMR) linewidth of 17.35 ± 3.07 MHz.
Growth Techniques Explored: Both high-pressure/moderate-temperature (HPHT, 8-10 GPa) and low-pressure/low-temperature (LPLT, 493 K hydrothermal) molecule-seeded synthesis routes were investigated to control nucleation and impurity incorporation.
Post-Processing Requirements: Successful color center creation required post-growth processing, including low-energy Si ion implantation (3 KeV) and high-temperature vacuum annealing (up to 1,100 °C).
Future Quantum Applications: The work lays the foundation for developing next-generation quantum sensors, including coupled NV centers (quantum registers) and magnetic gradiometers, requiring precise isotopic control (C¹³, N¹⁵).

Technical Specifications

The following hard data points were extracted from the analysis of FND synthesis and characterization:

Parameter	Value	Unit	Context
Target FND Size	< 10	nm	Required for biological applications (e.g., nuclear membrane passage)
HPHT Synthesis Pressure	8 - 10	GPa	Diamond Anvil Cell (DAC) experiments
HPHT Growth Temperature (Slow)	400	°C	Associated with low nitrogen incorporation
HPHT Growth Temperature (Fast)	650	°C	Associated with higher nitrogen incorporation
LPLT Hydrothermal Temperature	493 (220)	K (°C)	Used for nitrated aromatic hydrocarbon precursors
Si Implantation Energy	3	KeV	Used for shallow implantation to create SiV centers
High-T Annealing Temperature	1,100	°C	Vacuum annealing for color center activation
Low-T ODMR Linewidth (Mean ± SD)	17.35 ± 3.07	MHz	Indicates low P1 nitrogen content and high quality
High-T ODMR Linewidth (Mean ± SD)	23.44 ± 3.04	MHz	Indicates higher P1 nitrogen content
Diamond Raman Shift	1,328	cm^-1	Confirmed in LPLT synthesized NDs
Cubic Diamond Lattice Spacing	(111)	Å	Confirmed via TEM diffraction pattern

Key Methodologies

The research employed a combination of novel bottom-up synthesis and established post-processing techniques to engineer the FNDs:

Precursor Selection: Utilization of nitrogen-containing diamondoid seed molecules (e.g., 1-Adamantylamine) combined with sp³-rich hydrocarbons (e.g., tetracosane) to control nucleation and introduce nitrogen impurities deterministically.
High-Pressure Synthesis (DAC): Growth performed at extreme pressures (8-10 GPa) and moderate temperatures (400°C-650°C) to study the effect of growth rate on impurity exclusion and NV charge stability.
Low-Pressure Hydrothermal Synthesis: Growth of sub-4 nm NDs using nitrated aromatic hydrocarbons (e.g., naphthalene) dissolved in 0.2 M NaOH at low temperatures (493 K).
Purification and Cleaning: Samples were subjected to high-temperature oxidation (550°C) to remove non-diamond carbon (graphite/amorphous carbon) and extensive dialysis to remove residual growth chemicals.
Color Center Creation:
- Implantation: Low-energy silicon ion implantation (3 KeV) was used to introduce SiV centers.
- Annealing: High-temperature vacuum annealing (up to 1,100°C) was performed to mobilize vacancies and activate the implanted species into stable color centers (NV^-, SiV).
Quantum Characterization: Verification of diamond quality and color center performance using Photoluminescence (PL) spectroscopy and Optically Detected Magnetic Resonance (ODMR) to measure charge stability, zero-field splitting, and coherence-limiting linewidths.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-purity, precisely engineered diamond materials, both as substrates for FND anchoring and as bulk material for comparative studies. 6CCVD’s advanced MPCVD capabilities are ideally suited to support the replication and extension of this quantum biosensing research.

Research Requirement / Future Goal	6CCVD Solution & Capability	Technical Advantage for Quantum Sensing
High-Quality Substrates (For FND anchoring/growth)	Optical Grade Single Crystal Diamond (SCD)	SCD wafers up to 500 µm thick, polished to Ra < 1 nm. Provides an ultra-low defect platform essential for minimizing surface quenching effects and maximizing FND coherence times.
Custom Doping for Color Centers (N, Si, S, C¹³, N¹⁵)	Precision MPCVD Doping Services	While the paper uses implantation, 6CCVD offers controlled in-situ incorporation of Nitrogen (N) and Boron (B) during growth, enabling the creation of high-purity, low-P1 diamond necessary for long-coherence NV centers.
Isotopic Control (C¹³/N¹⁵ for quantum memory)	Isotopically Pure Diamond Growth	Capability to grow diamond using isotopically enriched precursors (e.g., C¹² or C¹³). This directly supports the goal of creating NV quantum registers with long-term quantum memories.
Custom Dimensions & Integration (Microfluidics, quantum chips)	Custom Dimensions & Laser Cutting	Plates/wafers available up to 125mm (PCD). Custom laser cutting and shaping services allow researchers to integrate diamond sensors into complex microfluidic or quantum chip architectures.
Quantum Device Integration (ODMR circuitry, Gradiometers)	Advanced Metalization Services	Internal capability for depositing thin films of Au, Pt, Pd, Ti, W, and Cu. This is crucial for fabricating the microwave/RF transmission lines required for high-fidelity ODMR measurements and coupled NV experiments.
Engineering Support (Material selection and optimization)	In-House PhD Engineering Team	6CCVD provides expert consultation on material selection, doping levels, and surface preparation to optimize diamond properties for similar NV/SiV quantum biosensing projects.

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

View Original Abstract

There is an increasing interest in the sensing of magnetic, electric, and temperature effects in biological systems on the nanoscale. While there are existing classical sensors, the possibility of using quantum systems promises improved sensitivity and faster acquisition time. So far, much progress has been made in diamond color centers like the nitrogen-vacancy (NV) which not only satisfy key requirements for biosensing, like extraordinary photostability and non-toxicity, but they also show promise as room-temperature quantum computers/sensors. Unfortunately, the most-impressive demonstrations have been done in bulk diamond, since NVs in fluorescent nanodiamonds (FNDs) tend to have inferior properties. Yet FNDs are required for widespread nanoscale biosensing. In order for FND-based quantum sensors to approach the performance of bulk diamond, novel approaches are needed for their fabrication. To address this need we discuss opportunities for engineering the growth of FNDs.

Tech Support

Original Source

DOI: https://doi.org/10.3389/frqst.2023.1202231

References

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