In Situ Measurement of Intracellular Thermal Conductivity Using Diamond Nanoparticle
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | Seibutsu Butsuri |
| Authors | Shingo Sotoma |
| Institutions | The University of Osaka |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research details the development and application of a novel hybrid nanosystem, Fluorescent Nanodiamonds coated with Polydopamine (FND-PDA), for high-resolution, localized measurement of intracellular thermal conductivity.
- Core Value Proposition: Integration of a quantum thermometer (NVC in FND) and a photothermal heater (PDA) into a single nanoparticle allows in situ thermal conductivity measurement at the nanoscale, overcoming limitations of bulk methods (e.g., 3ω method).
- Sensing Mechanism: The temperature rise of the FND-PDA probe upon irradiation is inversely proportional to the thermal conductivity of the immediate surrounding environment.
- High Precision: The system utilizes Optically Detected Magnetic Resonance (ODMR) for temperature readout, achieving a high resolution of 0.1 °C.
- Key Finding (Intracellular): The measured thermal conductivity inside HeLa and MCF-7 cells is approximately 0.11 W/mK, which is significantly lower (about 1/6th) than that of pure water (0.61 W/mK).
- Biological Implication: The low thermal conductivity and high spatial variability observed suggest that localized temperature gradients within the cell are substantial enough to potentially regulate specific biochemical reactions.
- Robustness: The NVC sensor is embedded within the rigid diamond lattice, ensuring its temperature measurement is robust against variations in the cellular environment (pH, viscosity, salt concentration).
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Intracellular Thermal Conductivity | 0.11 | W/mK | Measured in HeLa and MCF-7 cells |
| Temperature Rise (HeLa) | 3.0 ± 1.0 | °C | Measured by FND-PDA upon photothermal heating |
| Temperature Rise (MCF-7) | 2.9 ± 0.8 | °C | Measured by FND-PDA upon photothermal heating |
| ODMR Temperature Resolution | 0.1 | °C | High-precision quantum sensing method |
| All-optical (ZPL) Temperature Resolution | 0.5 | °C | Alternative method using Zero Phonon Line shift |
| ZPL Wavelength Shift Sensitivity | 0.015 | nm/K-1 | Required sensitivity for all-optical measurement |
| Water Thermal Conductivity (Reference) | 0.61 | W/mK | Used for system validation |
| Air Thermal Conductivity (Reference) | 0.026 | W/mK | Used for system validation |
| Mineral Oil Thermal Conductivity (Reference) | 0.135 | W/mK | Used for system validation |
| NVC Energy State | Spin Angular Momentum 1 | - | Quantum state used for magnetic resonance |
| NVC Base State Splitting (D) | Temperature Dependent | MHz | Zero-Field Splitting used for ODMR readout |
Key Methodologies
Section titled “Key Methodologies”The methodology centers on creating a dual-function nanoparticle (FND-PDA) and employing high-resolution quantum sensing techniques for readout.
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Probe Synthesis (FND-PDA):
- Fluorescent Nanodiamonds (FNDs), containing Nitrogen-Vacancy Centers (NVCs), are synthesized or acquired.
- The FND surface is coated with Polydopamine (PDA), a polymer derived from dopamine, which serves as the photothermal heating element.
- The resulting FND-PDA hybrid acts as a self-contained, localized heater and thermometer.
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Heating Mechanism (PDA):
- The PDA coating is irradiated with light (wavelength not specified, but typically visible/near-infrared for photothermal effect).
- PDA absorbs the light and converts the energy into heat, generating a localized temperature increase.
-
Temperature Sensing (FND/NVC):
- The NVC center within the FND measures the temperature of the immediate surrounding environment (the PDA/cytoplasm interface).
- ODMR (Optically Detected Magnetic Resonance) Method: This is the preferred method due to its high resolution (0.1 °C). It measures the shift in the zero-field splitting (D) of the NVC electronic spin states, which is highly sensitive to temperature.
- Alternative: All-optical measurement relies on the shift of the Zero Phonon Line (ZPL) in the fluorescence spectrum, offering lower resolution (0.5 °C).
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Intracellular Delivery and Measurement:
- FND-PDA nanoparticles are introduced into living cells (HeLa and MCF-7).
- The temperature rise (ΔT) is measured by the NVC upon irradiation.
- Thermal Conductivity Calculation: The measured ΔT is inversely correlated with the thermal conductivity (κ) of the surrounding medium. Calibration curves established using reference liquids (air, water, mineral oil) are used to convert ΔT into κ.
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Data Validation:
- Bayesian statistical analysis was employed to confirm that the observed large variability in temperature rise among individual nanoparticles was genuinely due to differences in local thermal conductivity within the cytoplasm, rather than inherent variations in the FND-PDA particles themselves.
Commercial Applications
Section titled “Commercial Applications”This technology leverages the unique properties of NVC nanodiamonds and localized thermal control, applicable across several high-tech sectors.
| Application Area | Specific Use Case | Technical Relevance |
|---|---|---|
| Quantum Sensing & Metrology | High-resolution temperature mapping in complex environments (e.g., biological systems, microfluidic chips). | Utilizes the superior coherence and stability of NVC centers for robust, non-invasive sensing. |
| Biomedical Research & Diagnostics | Monitoring localized thermal effects of drug delivery or hyperthermia treatments within single cells or organelles (e.g., mitochondria). | Provides crucial data on how heat dissipation affects protein folding and chemical reaction kinetics in vivo. |
| Micro/Nanoelectronics | Thermal management characterization in advanced semiconductor devices (MEMS/NEMS). | Allows mapping of heat flow and hot spots at the nanoscale, critical for preventing thermal runaway in high-density circuits. |
| Materials Science | Characterization of thermal transport properties in heterogeneous soft matter, polymers, and composite materials. | Enables precise measurement of thermal conductivity in environments where traditional bulk methods fail due to size constraints or complexity. |
| Nanoparticle Engineering | Development of multifunctional probes combining sensing (FND) and actuation (PDA) capabilities for targeted cellular manipulation. | Focuses on surface functionalization and integration of disparate material properties (quantum emitter + photothermal absorber). |
View Original Abstract
ナノ温度計として機能する蛍光性ナノダイヤモンドとナノヒーターとして機能するポリドーパミンを融合させることによって，ナノ領域の熱伝導率を計測可能なナノシステムを新開発した．細胞の熱伝導率を計測した結果，従来考えられてきた水よりも著しく低く，細胞内構造に由来する大きなばらつきを持つことが示唆された．