Fiber-optic control and thermometry of single-cell thermosensation logic

At a Glance

Metadata	Details
Publication Date	2015-11-13
Journal	Scientific Reports
Authors	И. В. Федотов, N. A. Safronov, Yulia G. Ermakova, Mikhail E. Matlashov, D. A. Sidorov‐Biryukov
Institutions	Institute of Bioorganic Chemistry, Russian Quantum Center
Citations	50
Analysis	Full AI Review Included

Technical Documentation & Analysis: Fiber-Optic Diamond Thermometry

Executive Summary

This paper presents a foundational development in cellular thermogenetics, utilizing a specialized diamond-based fiber-optic probe for ultra-localized heating and simultaneous thermometry at the single-cell level. 6CCVD is positioned as the ideal material partner to replicate and advance this technology due to our expertise in high-NV CVD diamond synthesis and custom microfabrication.

Core Value Proposition: Demonstration of precise, localized temperature control and measurement in biological systems using an integrated fiber-optic probe and a diamond microcrystal quantum sensor.
Methodology: The diamond microcrystal serves a dual purpose: it acts as a localized heat source (absorbing 532 nm laser light) and as a highly sensitive thermometer via the temperature-dependent frequency shift of Optically Detected Magnetic Resonance (ODMR) of Nitrogen-Vacancy (NV) centers.
Key Material Requirement: Successful operation relies on high-quality, high-NV density diamond material (10¹⁶-10¹⁷ cm^-3) integrated with custom microwave transmission lines.
Achievement in Precision: Achieved temperature measurement accuracy > 0.1°C during calibration, enabling the determination of highly precise activation thresholds ($T_a \approx 27.3\text{°C}$) for TRPA1 channels in HEK-293 cells.
Technological Integration: The system successfully integrates optical delivery (laser heating/polarization), microwave manipulation (spin resonance), and local temperature sensing within a fiber-optic architecture suitable for complex cell culture environments.
6CCVD Advantage: We provide the required custom-sized, high-NV density Single Crystal Diamond (SCD) or Polycrystalline Diamond (PCD) materials and specialized metalization services necessary for advanced probe fabrication.

Technical Specifications

The core material and performance parameters extracted from the research paper are summarized below.

Parameter	Value	Unit	Context
Diamond Type	HPHT/CVD	N/A	High-pressure, high-temperature synthesis used; necessary for high NV concentration.
Required NV Center Density	10¹⁶-10¹⁷	cm^-3	Required concentration for efficient ODMR thermometry signal generation.
Diamond Microcrystal Diameter	30-250	µm	Dimensions specified for attachment to fiber tip.
Thermometry Sensitivity (Calibration Slope)	≈ -75 ± 2	kHz/K	Slope of the zero-field splitting frequency versus temperature dependence (34°C to 49°C range).
Temperature Measurement Accuracy	> 0.1	°C	Achieved accuracy during thermostat calibration.
Optical Fiber Core Diameter	200	µm	Used for 532 nm heating/polarization laser delivery.
Microwave Transmission Line	Two-Wire Copper, 50	µm	Used to deliver 2.87 GHz microwave field for NV manipulation.
Heating Laser Wavelength	532	nm	CW Nd:YAG second harmonic output.
Cell Activation Threshold ($T_a$) Mean	27.3 ± 0.6	°C	For HEK-293 cells expressing rattlesnake TRPA1.
Median Activation Temperature ($T_m$) Mean	28.0 ± 0.5	°C	Corresponds to the median point of the TRPA1 activation curve.

Key Methodologies

The experiment successfully employed a multi-modal fiber-optic probe combining thermal, optical, and microwave actuation:

Diamond Sensor Integration: High-NV density diamond microcrystals (30-250 µm) were mechanically manipulated and fixed via adhesive to the 200 µm core diameter tip of an optical fiber.
Microwave Circuit Fabrication: A two-wire copper transmission line (50 µm diameter) was integrated alongside the fiber, creating a short-circuit loop near the diamond to generate a localized microwave field maximum for electron spin manipulation.
Localized Heating & Polarization: Continuous-Wave (CW) 532 nm laser radiation transmitted through the fiber was absorbed by the diamond, establishing a spherical temperature gradient (T(r)) in the cell culture and simultaneously spin-polarizing the NV centers ($m_s=0$ state).
Quantum Thermometry (ODMR): A microwave field was applied to couple the spin sublevels. The resultant dip in the photoluminescence (PL) yield (Optically Detected Magnetic Resonance, ODMR) was measured as a function of microwave frequency. The temperature was inferred from the temperature-dependent shift of this ODMR resonance frequency.
Biological Verification: A 473 nm laser was used to excite the G-GECO 1.2 calcium indicator. Activation of the TRPA1 channels was confirmed by monitoring the increase in green fluorescence, which signifies enhanced Ca²⁺ ion flow caused by the diamond’s localized heating.

6CCVD Solutions & Capabilities

6CCVD provides the specialized MPCVD diamond materials and precision engineering services necessary to manufacture and optimize the quantum sensors used in this localized thermometry research. Our capabilities ensure high fidelity and reproducibility for complex biophysics applications.

Applicable Materials for Replication and Extension

To replicate or advance the fiber-optic thermometry probe design, researchers require diamond with precise defect engineering and physical dimensions.

6CCVD Material Grade	Specification Alignment	Rationale and Value Proposition
High-NV SCD/PCD	Controlled NV density (10¹⁶-10¹⁷ cm^-3) achievable through optimized Nitrogen doping during MPCVD growth.	Guarantees the necessary high concentration of NV centers for strong ODMR signal contrast and superior thermal sensitivity (key to the ≈ -75 kHz/K slope).
Optical Grade SCD Wafers	Available in thicknesses from 0.1 µm to 500 µm, up to 125mm in size, with Ra < 1nm polishing.	Provides stable, high-quality starting material for laser cutting or mechanical processing into customized micro-tips or planar sensing substrates.
Polycrystalline Diamond (PCD)	High purity PCD available up to 500 µm thickness and 125mm size.	Can serve as an economical, highly thermally conductive substrate alternative where single crystal coherence is not strictly essential, provided grain boundaries do not compromise localized ODMR readings.

Customization Potential

The successful fabrication of the sensor probe relies heavily on custom dimensions and integration methods, areas where 6CCVD excels:

Precision Diamond Shaping: 6CCVD offers precision laser cutting and dicing to produce microcrystals or custom-shaped diamond tips in the 30 µm to 250 µm diameter range used in this study, ensuring consistent geometry for predictable thermal gradients.
Integrated Metalization Services: While the paper used external copper wires, 6CCVD offers in-house thin-film metal deposition (Au, Pt, Ti, W, Cu) directly onto diamond surfaces. This capability allows for the creation of superior integrated microwave micro-antennae or strip-lines, improving coupling efficiency and thermal stability compared to glued external wires.
Surface Finishes: For future studies aiming for direct cellular integration or enhanced optical throughput, 6CCVD provides ultra-low roughness polishing (Ra < 1 nm for SCD, < 5 nm for inch-size PCD).

Engineering Support

6CCVD’s in-house PhD material science team offers expert assistance in specifying optimal diamond properties for quantum sensing. We consult on:

Material Choice: Selection between SCD (for superior spin coherence/longer $T_2^*$) and PCD (for cost and scalability) based on specific experimental requirements (e.g., maximizing coherence time versus signal throughput).
NV Defect Optimization: Fine-tuning nitrogen doping levels to meet the specific 10¹⁶-10¹⁷ cm^-3 density requirement for applications in Localized Thermogenetics and Quantum Nanometry.
Probe Design Consultation: Assisting engineers in designing metalization patterns and custom diamond geometries for next-generation fiber-integrated quantum sensors.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/srep15737