Lightly Boron-Doped Nanodiamonds for Quantum Sensing Applications

At a Glance

Metadata	Details
Publication Date	2022-02-10
Journal	Nanomaterials
Authors	Masfer Alkahtani, Д. К. Жарков, A. V. Leontyev, A. G. Shmelev, В. Г. Никифоров
Institutions	King Abdulaziz City for Science and Technology, Kazan Scientific Center
Citations	8
Analysis	Full AI Review Included

Executive Summary

The research demonstrates the successful engineering of lightly Boron-Doped Nanodiamonds (BNDs) for simultaneous NIR heating and high-sensitivity quantum sensing, creating promising dual-function bio-probes.

Dual Functionality: BNDs are designed for use in hyperthermia/thermoablation therapy (heating) combined with real-time, nanoscale temperature and magnetic field sensing (quantum sensing).
Enhanced Heating: BNDs exhibit strong absorption around 800 nm, enabling efficient heating. Under 808 nm laser irradiation (50 W·cm^-2), BND solutions showed a 15 °C temperature rise, significantly higher than undoped nanodiamonds (2 °C).
NV Center Stabilization: Nitrogen (N) implantation (50 keV, 2 x 10¹² ion/cm²) and subsequent annealing were critical to stabilize the desired negatively charged NV^- center, overcoming the quenching effect typically caused by boron acceptors.
High Thermal Sensitivity: The NV^- centers in the BNDs achieved a thermal sensitivity of 250 mK/√Hz, suitable for monitoring temperature changes across the biological range (298 K to 330 K).
Viable Spin Coherence: Despite the boron co-doping, the NV centers maintained usable spin properties, demonstrating a longitudinal relaxation time (T₁) of 370 µs and a spin coherence time (T₂) of 5 µs, supporting quantum sensing applications.

Technical Specifications

Parameter	Value	Unit	Context
Boron Doping Level	~0.5	wt%	Lightly doped BNDs
Nanodiamond Size (Average)	50-70	nm	Used in suspension
Heating Wavelength (NIR)	808	nm	Tissue transparency window
Heating Laser Intensity	50	W·cm^-2	Continuous irradiation test
Temperature Rise (BNDs)	15	°C	After 20 min irradiation
NV Center Thermal Sensitivity (η)	250	mK/√Hz	Calculated sensitivity
ODMR Frequency Shift Slope (dM/dT)	-72	kHz/K	Temperature calibration
ODMR Linewidth (Γ)	17	MHz	Inhomogeneous width
ODMR Contrast (C)	4	%	Ensemble measurement
Spin Longitudinal Relaxation (T₁)	370	µs	NV center ground state
Spin Coherence Time (T₂)	5	µs	Measured via Hahn-echo sequence
Nitrogen Implantation Energy	50	keV	NV center creation
Nitrogen Implantation Dose	2 x 10¹²	ion/cm²	NV center creation
Annealing Temperature	750	°C	Vacuum annealing for 30 min

Key Methodologies

The lightly boron-doped nanodiamonds (BNDs) were processed through a series of chemical and physical steps to optimize NV center stability and concentration for quantum sensing.

Acid Cleaning:
- BNDs (~0.5 wt% Boron) were cleaned in a boiling mixture of Nitric and Sulfuric acids (HNO₃:H₂SO₄ = 1:1) at 120 °C.
- Purpose: Selectively etch graphitic carbon from the ND surfaces.
Surface Oxidation:
- Air oxidation was performed at 550 °C for 10 minutes.
- Purpose: Remove residual sp² carbon that could quench NV center luminescence and block ion implantation.
Nitrogen Implantation:
- Nitrogen ions were implanted at 50 keV energy with a dose of 2 x 10¹² ion/cm².
- Purpose: Introduce substitutional nitrogen (P1) centers, which act as donors to stabilize the NV^- charge state.
NV Center Formation (Annealing):
- Samples were annealed in a vacuum at 750 °C for 30 minutes.
- Purpose: Mobilize vacancies to combine with implanted nitrogen atoms, forming the NV centers.
Optical and Spin Characterization:
- A custom-built confocal scanning microscope (equipped with 532 nm and 808 nm lasers) was used for measurements.
- Optically Detected Magnetic Resonance (ODMR) was performed by sweeping microwave frequencies (2700 MHz to 3000 MHz) while monitoring fluorescence.
- Pulsed microwave sequences were used to measure Rabi oscillations, spin longitudinal relaxation (T₁), and spin coherence time (T₂, via Hahn-echo).

Commercial Applications

The unique combination of NIR absorption and quantum sensing capabilities positions these co-doped nanodiamonds for high-impact applications in biomedicine and advanced metrology.

Targeted Cancer Therapy (Hyperthermia/Thermoablation):
- BNDs serve as highly efficient photothermal agents, selectively heating tumor cells when excited by deep-penetrating 808 nm lasers, minimizing damage to surrounding healthy tissue.
In Vivo Nanoscale Thermometry:
- Enables real-time, non-invasive temperature monitoring inside biological systems (e.g., living cells, embryos) during hyperthermia treatment, ensuring precise thermal dosage control.
Advanced Bio-Sensing and Diagnostics:
- The NV center’s sensitivity allows for nanoscale imaging and sensing of local magnetic fields, potentially enhancing Magnetic Resonance Imaging (MRI) contrast or probing cellular magnetic environments.
Quantum Information Science:
- The stable NV^- centers in the co-doped diamond lattice provide robust solid-state qubits, suitable for developing quantum memory or quantum computing components, especially where integration with thermal management is required.
Materials Science Metrology:
- Used as atomic-sized sensors to diagnose magnetic properties and spin textures in novel materials, such as superconductors or magnetic films, under ambient conditions.

View Original Abstract

Unlike standard nanodiamonds (NDs), boron-doped nanodiamonds (BNDs) have shown great potential in heating a local environment, such as tumor cells, when excited with NIR lasers (808 nm). This advantage makes BNDs of special interest for hyperthermia and thermoablation therapy. In this study, we demonstrate that the negatively charged color center (NV) in lightly boron-doped nanodiamonds (BNDs) can optically sense small temperature changes when heated with an 800 nm laser even though the correct charge state of the NV is not expected to be as stable in a boron-doped diamond. The reported BNDs can sense temperature changes over the biological temperature range with a sensitivity reaching 250 mK/√Hz. These results suggest that BNDs are promising dual-function bio-probes in hyperthermia or thermoablation therapy as well as other quantum sensing applications, including magnetic sensing.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano12040601

References

2018 - Fluorescent nanodiamonds: Past, present, and future [Crossref]
2012 - Room-Temperature Quantum Bit Memory Exceeding One Second [Crossref]
2011 - Nanodiamond Therapeutic Delivery Agents Mediate Enhanced Chemoresistant Tumor Treatment [Crossref]
2017 - Nanometer-scale luminescent thermometry in bovine embryos [Crossref]
2013 - Nanometre-scale thermometry in a living cell [Crossref]
2018 - Fluorescent nanodiamonds for luminescent thermometry in the biological transparency window [Crossref]
2017 - Nanodiamond-enhanced MRI via in situ hyperpolarization [Crossref]
2015 - Single proteins under a diamond spotlight [Crossref]
2013 - Optical magnetic imaging of living cells [Crossref]
2011 - Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells [Crossref]