| Metadata | Details |
|---|
| Publication Date | 2022-01-01 |
| Journal | Biophysics and Physicobiology |
| Authors | Shingo Sotoma, Hirotaka Okita, Shunsuke Chuma, Yoshie Harada |
| Institutions | The University of Osaka, Quantum (Australia) |
| Citations | 13 |
| Analysis | Full AI Review Included |
- Core Value Proposition: Fluorescent Nanodiamonds (FNDs), incorporating Nitrogen-Vacancy (NV) centers, serve as robust, biocompatible quantum sensors for measuring physical quantities (angle, temperature, thermal conductivity) within the nanometric region of single living cells.
- Sensing Mechanism: FNDs utilize Optically Detected Magnetic Resonance (ODMR) to optically read out the quantum states of the NV electron spin, providing high sensitivity and stability without photobleaching.
- Precision Measurements: The technology enables 3D rotational tracking of biomolecules (e.g., F1ATP-ase, EGFR) with an angular uncertainty of 3° (1.7 s resolution), linking membrane dynamics to intracellular cytoskeleton density.
- Intracellular Thermometry: FNDs measure local temperature by monitoring the shift in the NV zero-field splitting (D). Measurements in living cells (e.g., HeLa, C. elegans) achieved a precision of 0.1 K (4-s measurement) and ±0.22 °C (in vivo).
- Thermal Conductivity Mapping: A hybrid polydopamine (PDA)-coated FND acts as a two-in-one heater/thermometer, revealing that intracellular thermal conductivity (e.g., 0.11 W/mK) is significantly lower than that of pure water.
- Development Challenge: Current FNDs (50-100 nm) are too large for precise organelle-specific sensing. Future work requires synthesizing smaller, single-digit nanometer FNDs that retain high fluorescence and ODMR signal quality.
| Parameter | Value | Unit | Context |
|---|
| FND Particle Size (General Use) | 50-100 | nm | Standard size for biomedical applications. |
| NV- Zero-Field Splitting (D) | 2870 | MHz | Triplet ground state splitting frequency. |
| Thermal Shift Coefficient (dD/dT) | -75 | kHz/K | Temperature dependence of D. |
| Temperature Sensing Precision (HeLa cells) | 0.1 | K | Achieved with 4-s measurement time (ODMR). |
| Temperature Sensing Precision (C. elegans) | ±0.22 | °C | Real-time in vivo measurement precision. |
| Angular Uncertainty (3D Tracking) | 3 | ° | Achieved at 1.7 s time resolution. |
| Intracellular Thermal Conductivity (HeLa/MCF-7) | 0.11 ± 0.04 | W/mK | Measured using FND-PDA hybrid sensor. |
| Intracellular Thermal Conductivity (Alternative Method) | 0.31 | W/mK | Measured using optically heated gold nanoparticles (Song et al.). |
| Thermal Diffusivity (Intracellular) | 2.7 x 10-8 | m2s-1 | Calculated from heat propagation (5.3-fold lower than water). |
| NV- Zero-Phonon Line (ZPL) | 637 | nm | Used for all-optical temperature sensing. |
| ZPL Thermal Shift | 0.015 | nm/K-1 | Wavelength shift used for all-optical sensing. |
- FND Synthesis and NVC Creation: Nanodiamonds are processed (often detonation synthesis followed by irradiation/annealing) to create stable Nitrogen-Vacancy (NV) centers, which are structurally protected deep within the robust diamond lattice.
- Surface Functionalization: FNDs are coated to achieve water solubility, colloidal stability, and biocompatibility. Common non-covalent coatings include Bovine/Human Serum Albumin (BSA/HSA) and Polyethyleneimine (PEI). Covalent coatings include Silica, Hyperbranched Polyglycerol (HPG), and Polydopamine (PDA).
- Optically Detected Magnetic Resonance (ODMR): The NV- centers are excited using a green laser (e.g., 532 nm). MW radiation is applied near the zero-field splitting frequency (2870 MHz) to induce electron spin magnetic resonance, resulting in a measurable decrease in fluorescence intensity (optical readout of quantum state).
- Angular Sensing (Tomographic Vector Magnetometry): A three-axis magnet system generates a known external magnetic field. The Zeeman splitting of the NV- spin sublevels is measured via ODMR. The magnitude of this splitting is dependent on the angle between the NV axis and the magnetic field vector, allowing 3D orientation tracking (roll-pitch-yaw).
- Temperature Sensing (ODMR): Temperature is determined by monitoring the shift in the NV- zero-field splitting frequency (D). This shift is calibrated against temperature and is used for robust intracellular thermometry, independent of local pH or viscosity.
- Thermal Conductivity Measurement (FND-PDA Hybrid): FNDs are coated with PDA. The PDA layer absorbs light and acts as a localized heater (photothermal effect). The FND NV center simultaneously measures the local temperature rise. The rate of heat dissipation allows calculation of the thermal conductivity of the surrounding intracellular environment.
- Quantum Sensing and Metrology: Development of highly localized, robust quantum sensors for non-magnetic physical quantities (temperature, strain, electric field) in complex environments.
- Nanomedicine and Drug Delivery: FNDs serve as stable, non-photobleaching fluorescent labels for long-term tracking of drug carriers or biomolecules, and as carriers themselves (e.g., FND-PEI for DNA delivery).
- Advanced Diagnostics: Spin-enhanced nanodiamond biosensing (using ODMR) offers ultrasensitive detection systems, such as the 105-fold sensitivity increase demonstrated in lateral flow immunoassays (e.g., COVID-19 detection).
- Biophysics Research Tools: Enabling quantitative, real-time measurement of cellular dynamics, including 6-D motion (3D translation and 3D rotation) of membrane proteins and monitoring metabolic activity in single mitochondria.
- Thermal Biology: Tools for mapping intracellular heat transfer and thermoregulation, crucial for understanding cellular processes like non-shivering thermogenesis and differentiation in stem cells.
View Original Abstract
Measuring physical quantities in the nanometric region inside single cells is of great importance for understanding cellular activity. Thus, the development of biocompatible, sensitive, and reliable nanobiosensors is essential for progress in biological research. Diamond nanoparticles containing nitrogen-vacancy centers (NVCs), referred to as fluorescent nanodiamonds (FNDs), have recently emerged as the sensors that show great promise for ultrasensitive nanosensing of physical quantities. FNDs emit stable fluorescence without photobleaching. Additionally, their distinctive magneto-optical properties enable an optical readout of the quantum states of the electron spin in NVC under ambient conditions. These properties enable the quantitative sensing of physical parameters (temperature, magnetic field, electric field, pH, etc.) in the vicinity of an FND; hence, FNDs are often described as âquantum sensorsâ. In this review, recent advancements in biosensing applications of FNDs are summarized. First, the principles of orientation and temperature sensing using FND quantum sensors are explained. Next, we introduce surface coating techniques indispensable for controlling the physicochemical properties of FNDs. The achievements of practical biological sensing using surface-coated FNDs, including orientation, temperature, and thermal conductivity, are then highlighted. Finally, the advantages, challenges, and perspectives of the quantum sensing of FND are discussed. This review article is an extended version of the Japanese article, In Situ Measurement of Intracellular Thermal Conductivity Using Diamond Nanoparticle, published in SEIBUTSU BUTSURI Vol. 62, p. 122-124 (2022).