Optimization of Wide-Field ODMR Measurements Using Fluorescent Nanodiamonds to Improve Temperature Determination Accuracy

At a Glance

Metadata	Details
Publication Date	2020-11-18
Journal	Nanomaterials
Authors	Tamami Yanagi, Kiichi Kaminaga, Wataru Kada, Osamu Hanaizumi, Ryuji Igarashi
Institutions	Japan Science and Technology Agency, Gunma University
Citations	9
Analysis	Full AI Review Included

Executive Summary

This research focuses on optimizing Optically Detected Magnetic Resonance (ODMR) measurements using fluorescent nanodiamonds (FNDs) to achieve highly accurate, wide-field temperature mapping in microenvironments.

Core Achievement: Demonstrated a method for highly accurate wide-field temperature imaging over a 210 x 210 µm area, suitable for monitoring multicellular systems.
Optimization Strategy: A Monte Carlo simulation was performed to identify the optimal microwave frequency sweep range for fitting the ODMR spectrum with two Lorentzian functions.
Key Finding (Sweep Range): The optimal sweep range was determined to be 2860-2880 MHz, which is narrower than typical ranges (e.g., 2850-2890 MHz).
Performance Improvement: This optimized sweep range improved the temperature determination accuracy by a factor of approximately 1.5x.
Achieved Accuracy: Temperature determination accuracy reached 1 K/Hz^1/2 or higher in the wide-field setup.
Biological Relevance: The method enables monitoring of tissue homeostasis, differentiation in multicellular systems, and organelle-level mesoscopic temperatures (e.g., mitochondria).

Technical Specifications

Parameter	Value	Unit	Context
Optimal ODMR Sweep Range	2860-2880	MHz	Determined via Monte Carlo simulation for highest accuracy
Accuracy Improvement Factor	~1.5	Factor	Improvement over the 2850-2890 MHz sweep range
Achieved Temperature Accuracy	1	K/Hz^1/2	Highest accuracy obtained in wide-field imaging
Wide-Field Imaging Area	210 x 210	µm	Area measured simultaneously
NV Center Axial Anisotropy (D)	2869.34 ± 1.31	MHz	Mean value derived from 200 bright spots
NV Center Rhombic Anisotropy (E)	4.21 ± 0.31	MHz	Mean value derived from 200 bright spots
Temperature Dependence of D	77	kHz/K	Proportional constant due to thermal expansion
Excitation Wavelength	532	nm	Green laser source
Excitation Power Density	~1	kW/cm²	Used for fluorescence imaging
Microwave Output Power	< 700	mW	Applied via 1.5-turn copper coil
FND Particle Size Range	50-100	nm	Particle size distribution of fluorescent nanodiamonds
NV Centers per Particle (Average)	40	Centers	Concentration in the FNDs used
Temperature Stability (Ambient)	± 0.1	K	Change restricted during 2 min measurements

Key Methodologies

The methodology involved the preparation of fluorescent nanodiamonds (FNDs), Monte Carlo simulation for optimization, and wide-field ODMR measurement validation.

1. Fluorescent Nanodiamond (FND) Preparation

Starting Material: Nanodiamond powder (Micron + MDA 0-0.10 µm).
NV Center Creation:
- Electron irradiation (2 MeV, 1.0 x 10¹⁸ e^-/cm²).
- Thermal annealing at 800 °C for 2 h under vacuum.
Surface Treatment:
- Oxidation at 550 °C for 2 h to remove surface graphite.
- Acid treatment using H₂SO₄:HNO₃ (9:1 v/v) at 70 °C for 3 days to obtain negatively charged NV centers.
Cleaning: Treated with 0.1 M NaOH (90 °C, 2 h) and 0.1 M HCl (90 °C, 2 h), followed by three Milli-Q washes.

2. ODMR Measurement Setup (Wide-Field Imaging)

Excitation: 532 nm green laser (1000 mW) focused to ~1 kW/cm² power density.
Detection: Fluorescence collected using a 20x dry objective (NA 0.75) and detected by an electron-multiplying CCD (EMCCD) camera.
Microwave Application: Microwaves generated by a signal generator (N5172B), amplified, and applied via a 1.5-turn copper coil (1 mm diameter).
Temperature Control: Ambient temperature around the setup was controlled and stabilized (± 0.1 K fluctuation over 2 min) to avoid periodic fluctuations from feedback regulation.

3. Optimization and Data Analysis

Model Parameters: ODMR frequency spectra were obtained from 200 FND bright spots to establish mean values for the model curve parameters (D, E, a₁, a₂, and γ).
Monte Carlo Simulation: Simulated 50 points of digital sweep data, adding Gaussian noise (0-20% of signal strength), and performed curve fitting using two Lorentzian functions to determine the optimal sweep range.
Optimal Range Application: ODMR spectra were acquired using a 100-point digital sweep (2 s total time) to compare the performance of the optimized 2860-2880 MHz range against the broader 2850-2890 MHz range.
Accuracy Evaluation: Temperature determination stability was calculated from the standard deviation of the determined D values (D_obs) over 100 consecutive measurements (1 s sweep time).

Commercial Applications

This optimized wide-field thermometry technique is critical for advancing quantitative measurements in biological and materials science fields requiring high spatial and temporal resolution.

Cell Biology and Medicine:
- Intracellular Thermometry: Quantitative measurement of mesoscale temperature distributions within cells and organelles (e.g., mitochondria).
- Tissue Homeostasis Monitoring: Wide-field monitoring of temperature dynamics in multicellular systems and tissues, relevant to understanding canceration and aging.
- Differentiation Studies: High-throughput image cytometry for monitoring the differentiation of large numbers of stem cells based on intracellular temperature changes.
Quantum Sensing and Metrology:
- Nanometer-Scale Sensors: Development of robust, highly accurate nanoprobes for temperature sensing in complex chemical and physical microenvironments.
Drug Discovery and Screening:
- High-throughput screening of drug candidates by monitoring their effect on cellular thermogenesis and metabolic activity.

View Original Abstract

Fluorescent nanodiamonds containing nitrogen-vacancy centers have attracted attention as nanoprobes for temperature measurements in microenvironments, potentially enabling the measurement of intracellular temperature distributions and temporal changes. However, to date, the time resolution and accuracy of the temperature determinations using fluorescent nanodiamonds have been insufficient for wide-field fluorescence imaging. Here, we describe a method for highly accurate wide-field temperature imaging using fluorescent nanodiamonds for optically detected magnetic resonance (ODMR) measurements. We performed a Monte Carlo simulation to determine the optimal frequency sweep range for ODMR temperature determination. We then applied this sweep range to fluorescent nanodiamonds. As a result, the temperature determination accuracies were improved by a factor ~1.5. Our result paves the way for the contribution of quantum sensors to cell biology for understanding, for example, differentiation in multicellular systems.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano10112282

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