Multifunctional Core/Shell Diamond Nanoparticles Combining Unique Thermal and Light Properties for Future Biological Applications

At a Glance

Metadata	Details
Publication Date	2023-12-12
Journal	Nanomaterials
Authors	S. A. Grudinkin, Kirill Bogdanov, V. A. Tolmachev, М. А. Баранов, Ilya E. Kaliya
Institutions	Ioffe Institute, ITMO University
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Multifunctional Core/Shell Diamond Nanoparticles

Executive Summary

This research demonstrates a significant advancement in diamond-based theranostics by successfully synthesizing multifunctional Core/Shell Diamond Nanoparticles (CSNDs) using a two-stage Hot Filament Chemical Vapor Deposition (HFCVD) process.

Core Functionality: The core consists of heavily Boron-Doped Diamond (BDD) (64,000 ppm B/C), engineered for high absorption of 532 nm laser radiation, enabling efficient photoinduced heating (hyperthermia).
Shell Functionality: The shell is a thin, transparent CVD diamond layer containing negatively charged Silicon-Vacancy (SiV^-) color centers, providing both fluorescent imaging and precise local nanothermometry.
Thermometry Mechanism: Temperature sensing is achieved by monitoring the spectral shift of the SiV Zero-Phonon Line (ZPL), which shifts from 738.9 nm to 741.1 nm upon heating.
Biomedical Relevance: The CSNDs achieved temperatures relevant for photothermal therapy (45-50 °C) at incident laser power densities (44-52 W/cm²) considered safe for biological systems.
Synthesis Method: The two-stage HFCVD technique successfully created a functional heterostructure, demonstrating precise control over doping profiles (B in the core, SiV in the shell) and material interfaces.
Proof of Concept: This work provides a robust proof-of-concept for integrating distinct functional properties (heating, sensing, imaging) into a single diamond nanostructure for advanced biomedical applications.

Technical Specifications

The following hard data points were extracted from the synthesis and characterization of the Core/Shell Diamond Nanoparticles (CSNDs):

Parameter	Value	Unit	Context
Core Material	Boron-Doped Diamond (BDD)	N/A	High absorption photothermal core
Core Doping Concentration (B/C)	64,000	ppm	Ratio in the gas mixture (Diborane/Methane)
Shell Material	CVD Diamond with SiV Centers	N/A	Luminescent shell for sensing/imaging
Core Size (Diameter)	800-1100	nm	Size of the initial BND particle
Shell Thickness	~500	nm	Thickness of the SiV-doped CVD layer
Total Particle Diameter	~1.3	µm	Final Core/Shell Nanodiamond size
SiV ZPL Wavelength (Baseline)	738.9	nm	Measured at low excitation power
SiV ZPL Wavelength (Max Shift)	741.1	nm	Observed at 52.0 mW incident power
Target Hyperthermia Temperature	45-50	°C	Temperature range relevant for thermotherapy
Laser Power Density (Hyperthermia)	44-52	W/cm²	Required to achieve 45-50 °C
Maximum Observed Temperature	150	°C	Achieved at 40 mW (532 nm) laser power
Substrate Material	Synthetic Opal Film on Fused Silica	N/A	Used to promote spherical particle growth

Key Methodologies

The multifunctional CSNDs were fabricated using a highly controlled, two-stage Hot Filament Chemical Vapor Deposition (HFCVD) process:

Substrate Preparation:
- Synthetic opal films (9-15 monolayers of 250 nm a-SiO₂ spheres) were grown on fused silica wafers.
- The surface was seeded with detonation nanodiamonds (~4 nm) at a density of ~10⁷ cm^-2 to serve as nucleation centers.
Stage 1: Boron-Doped Core (BND) Synthesis:
- Method: HFCVD.
- Substrate Temperature: 800 °C.
- Tungsten Coil Temperature: 2000-2200 °C.
- Reactor Pressure: 48 Torr.
- Gas Flow: Hydrogen (480 sccm), Methane (4%).
- Doping Source: Diborane (B₂H₆) introduced to achieve a 64,000 ppm Boron-to-Carbon (B/C) ratio.
- Growth Time: ~3 hours, resulting in 0.8-1.2 µm BND cores.
Stage 2: SiV-Embedded Shell Synthesis:
- Method: HFCVD applied to the BND cores.
- Substrate Temperature: 750 °C.
- Tungsten Coil Temperature: 2000-2200 °C.
- Reactor Pressure: 50 Torr.
- Gas Flow: Hydrogen (500 sccm), Methane (4%).
- Si Source: A crystalline silicon wafer was placed on the substrate holder, allowing atomic hydrogen etching to generate volatile SiH_x radicals, which were incorporated into the growing diamond shell.
- Growth Time: 1.5 hours, resulting in a ~500 nm transparent shell containing luminescent SiV centers.
Post-Processing (Potential):
- The SiO₂ substrate can be removed via etching (Hydrofluoric acid/Ammonium Fluoride solution) to obtain a colloidal suspension of CSNDs for direct biomedical application.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to support and scale the development of advanced diamond theranostic platforms, offering the precise material control and customization required to replicate and extend this core/shell technology.

Applicable Materials and Doping Control

Research Requirement	6CCVD Material Solution	Customization & Control
High-Absorption Core	Heavy Boron-Doped Diamond (BDD)	We provide BDD materials with highly controlled doping profiles, essential for achieving the metallic conductivity and high absorption coefficient demonstrated in the core. Our MPCVD process ensures uniform boron incorporation up to the concentrations required for photothermal efficiency.
Luminescent Shell/Sensing	Optical Grade Single Crystal Diamond (SCD) with SiV Centers	6CCVD specializes in introducing Group IV color centers (SiV, GeV) during growth. We guarantee high-density, stable SiV^- centers in our SCD films, optimized for intense, narrowband Zero-Phonon Line (ZPL) emission near 738 nm, crucial for accurate nanothermometry and bioimaging.
Complex Heterostructures	Custom Multi-Layer CVD Growth	Replicating the two-stage core/shell structure requires precise control over gas switching and temperature profiles. 6CCVD offers custom growth recipes to seamlessly transition from heavily doped BDD to transparent, SiV-doped SCD/PCD layers, maintaining structural integrity and functional separation.

Customization Potential & Processing Services

The successful implementation of this technology relies on precise material dimensions and potential surface modification, areas where 6CCVD excels:

Custom Dimensions: While the paper focused on 1.3 µm particles, 6CCVD can provide large-area Polycrystalline Diamond (PCD) wafers up to 125mm or thick SCD substrates up to 10mm. This allows researchers to scale up synthesis or utilize bulk material for micro-structuring.
Thickness Control: We offer precise thickness control for both SCD and PCD layers, ranging from 0.1 µm to 500 µm, enabling optimization of the shell thickness for maximum SiV signal intensity without compromising core heating efficiency.
Surface Finish: For optimal optical coupling and subsequent biological functionalization, 6CCVD provides industry-leading polishing: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
Metalization Services: Biomedical applications often require specific surface chemistry. 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) to prepare the diamond surface for bio-conjugation, streamlining the transition from material synthesis to functional device testing.

Engineering Support

6CCVD’s in-house PhD team provides authoritative professional support to accelerate your research:

Material Selection Optimization: We assist researchers in selecting the optimal diamond matrix (SCD vs. PCD) and doping strategy for similar photoinduced hyperthermia and nanothermometry projects, ensuring the material properties meet the required thermal and optical performance metrics.
Recipe Development: Our experts can help refine CVD parameters (pressure, temperature, gas ratios) to achieve specific SiV ZPL characteristics (e.g., narrow linewidth, high intensity) or tailor BDD absorption profiles for different laser wavelengths (e.g., 633 nm or NIR sources, as suggested for future work).

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

View Original Abstract

We report the development of multifunctional core/shell chemical vapor deposition diamond nanoparticles for the local photoinduced hyperthermia, thermometry, and fluorescent imaging. The diamond core heavily doped with boron is heated due to absorbed laser radiation and in turn heats the shell of a thin transparent diamond layer with embedded negatively charged SiV color centers emitting intense and narrowband zero-phonon lines with a temperature-dependent wavelength near 738 nm. The heating of the core/shell diamond nanoparticle is indicated by the temperature-induced spectral shift in the intensive zero-phonon line of the SiV color centers embedded in the diamond shell. The temperature of the core/shell diamond particles can be precisely manipulated by the power of the incident light. At laser power safe for biological systems, the photoinduced temperature of the core/shell diamond nanoparticles is high enough to be used for hyperthermia therapy and local nanothermometry, while the high zero-phonon line intensity of the SiV color centers allows for the fluorescent imaging of treated areas.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano13243124

References

2022 - Conjugated Polymer Nanoparticles and Their Nanohybrids as Smart Photoluminescent and Photoresponsive Material for Biosensing, Imaging, and Theranostics [Crossref]
2020 - Boron-Doped Nanodiamonds as Anticancer Agents: En Route to Hyperthermia/Thermoablation Therapy [Crossref]
2017 - Boron-Doped Nanodiamonds as Possible Agents for Local Hyperthermia [Crossref]
2021 - Nanodiamonds: Synthesis, Properties, and Applications in Nanomedicine [Crossref]
2013 - Targeting Polymeric Fluorescent Nanodiamond-Gold/Silver Multi-Functional Nanoparticles as a Light-Transforming Hyperthermia Reagent for Cancer Cells [Crossref]
2023 - A Plasmonic Fluorescent Ratiometric Temperature Sensor for Self-Limiting Hyperthermic Applications Utilizing FRET Enhancement in the Plasmonic Field [Crossref]
2022 - Laser Synthesized Nanodiamonds with Hyper-Branched Polyglycerol and Polydopamine for Combined Imaging and Photothermal Treatment [Crossref]