Noncovalent force spectroscopy using wide-field optical and diamond-based magnetic imaging

At a Glance

Metadata	Details
Publication Date	2019-11-18
Journal	Journal of Applied Physics
Authors	S. Lourette, L. Bougas, M. Kayci, S. Xu, D. Budker
Institutions	University of Houston, Helmholtz Institute Mainz
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond-Based Force Spectroscopy

Executive Summary

This research demonstrates a significant advancement in biomolecular force spectroscopy by integrating diamond Nitrogen-Vacancy (NV) center magnetometry with Force-Induced Remnant Magnetization Spectroscopy (FIRMS). This approach is critical for high-throughput diagnostics and drug screening.

Quantum Sensing for Biomolecular Studies: Realization of a diamond-based FIRMS technique utilizing an ensemble of NV color centers for high-sensitivity detection of noncovalent molecular interactions (e.g., biotin-streptavidin bonds).
Massively Enhanced Sensitivity: The NV-based detection system boosts the measured magnetic field signal by nine orders of magnitude (maximum measured field 0.3 G) compared to traditional vapor cell magnetometers.
High Resolution & Parallelism: Achieves optical diffraction-limited, single-microsphere resolution, enabling the simultaneous tracking and quantitative force measurement of dozens of individual particles.
Material Requirements: Requires high-purity, electronic grade CVD diamond plates (≈100 µm thick) implanted with ¹⁵N ions to create a shallow (≈100 nm), high-density NV layer.
Quantitative Force Measurement: Successfully quantified the rupture force of biotin-streptavidin bonds, estimating the value at 20(8) pN under oscillating force application.
Future Scalability: The technique is highly adaptable for massively parallel, lab-on-a-chip screening systems, promising utility in drug testing and diagnostics.

Technical Specifications

The following hard data points were extracted from the research paper detailing the material and experimental parameters:

Parameter	Value	Unit	Context
Diamond Substrate Type	Electronic Grade CVD	Plate	Used for NV center creation
Diamond Thickness	≈ 100	µm	Nominal thickness of plates
Target NV Layer Depth	≈ 100	nm	Uniform, high-density layer created via ¹⁵N implantation
¹⁵N Implantation Energy Range	10 to 100	keV	Range used across five implantation steps
Maximum ¹⁵N Implantation Dose	2.2.10¹³	cm^-2	Highest dose used (at 100 keV)
Annealing Temperature 1	800	°C	2 hours duration
Annealing Temperature 2	1100	°C	4 hours duration
Excitation Laser Wavelength	525	nm	Green diode laser
Applied Magnetic Field (Bias)	≈ 50	G	Aligned to one of the four NV axes
Zero-Field Splitting (NV)	2.8	MHz/G	Gyromagnetic ratio used for magnetic field conversion
Magnetic Microsphere Diameter (Mean)	2.10	µm	Streptavidin-coated ferro-magnetic particles
Microsphere Density	1.8	g/cm³	Polystyrene cores and CrO₂ coatings
Estimated Rupture Force (Biotin-Streptavidin)	20(8)	pN	Measured force value
Effective Loading Rate	≈ 70	pN/s	Calculated rate for oscillating force application
Maximum Measured Magnetic Field	0.3 (3 × 10^-5)	G (T)	Detected by NV ensemble

Key Methodologies

The experiment relied on precise material engineering and sophisticated optical/magnetic detection techniques:

Diamond Selection and Implantation: Electronic grade CVD diamond plates (≈100 µm) were selected. ¹⁵N ions were implanted across multiple energies (10-100 keV) and doses to achieve a uniform, high-density NV layer approximately 100 nm deep.
NV Center Activation: A two-step high-temperature annealing process (800 °C for 2 hours, then 1100 °C for 4 hours) was performed to mobilize vacancies and form the NV centers.
Surface Functionalization: The diamond surface was chemically functionalized using an Alkene-EG-COOH crosslinker, followed by bonding to biotin to create the target surface for streptavidin-coated microbeads.
Microfluidic Chamber Assembly: A sealed chamber was constructed using glass coverslips and a 150 µm silicone gasket, with the NV-side-up diamond attached to the bottom coverslip.
Force Application: Piezoelectric actuators were attached to the chamber and driven in parallel with sinusoidal pulses (5 ms duration, 5-10 kHz frequency) of gradually increasing amplitude (0 V_p-p to 50 V_p-p) to apply inertial force to the microbeads.
Magnetic Imaging (ODMR): A Continuous Wave (CW) excitation scheme was used. The 525 nm laser illuminated the NV layer, and the microwave frequency was swept across the $m_s = {0 \rightarrow +1}$ transition. Lock-in detection synchronized with the microwave source enhanced signal quality.
Correlated Detection: Wide-field optical imaging (white light) tracked particle detachment and movement, while magnetic imaging provided background-free detection of particle position and orientation, resolving subtle angular changes (10(2) degrees).

6CCVD Solutions & Capabilities

The success of this NV-based FIRMS technique hinges on the quality and precision of the diamond substrate. 6CCVD is uniquely positioned to supply the necessary high-specification materials and customization required to replicate, scale, and advance this research.

Research Requirement	6CCVD Solution & Capability	Sales Advantage
High-Purity Substrate	Optical Grade SCD Plates: We provide high-ppurity, low-strain Single Crystal Diamond (SCD) grown via MPCVD. This material is essential for achieving long NV coherence times ($T_2$) and maximizing the signal-to-noise ratio required for high-sensitivity magnetometry.	Guaranteed material quality optimized for quantum sensing applications.
Custom Dimensions & Thickness	SCD/PCD Customization: The paper used ≈100 µm thick plates. 6CCVD offers SCD from 0.1 µm to 500 µm, and robust substrates up to 10 mm thick. We can supply custom dimensions up to 125 mm (PCD) for scaling to massively parallel arrays.	Flexibility to match current specifications or scale up to high-throughput, inch-size lab-on-a-chip devices.
Surface Quality for Functionalization	Ultra-Smooth Polishing: Our SCD surfaces are polished to an atomic level (Ra < 1 nm). This ultra-smooth finish is critical for uniform chemical functionalization (e.g., Alkene-EG-COOH crosslinker) and minimizing non-specific binding in molecular studies.	Ensures reliable, reproducible surface chemistry and optimal particle-to-NV distance.
Integration of Microwave/Electrodes	In-House Metalization Services: The experiment required precise positioning of a microwave wire (0.2 mm from the surface). 6CCVD offers custom metalization (Au, Pt, Pd, Ti, W, Cu) directly onto the diamond surface, allowing researchers to integrate planar microwave waveguides or dielectrophoresis electrodes (as suggested for future work) directly into the device structure.	Streamlines device fabrication by providing integrated, high-precision metal layers.
Material for Force Calibration	Engineering Support for BDD: The force calibration relies on the mechanical stability of the chamber. For future work requiring integrated sensing or actuation, 6CCVD can provide Boron-Doped Diamond (BDD) films, which can be used as highly stable, chemically inert electrodes or micro-electromechanical systems (MEMS) components.	Access to specialized materials for advanced device integration and sensing.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing CVD diamond for quantum and biological sensing applications. We can assist researchers in selecting the optimal diamond grade, orientation, and surface preparation necessary to maximize NV center yield and coherence for similar diamond-based magnetic imaging projects.

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

View Original Abstract

A realization of the force-induced remnant magnetization spectroscopy technique of specific biomolecular binding is presented, where detection is accomplished with wide-field optical and diamond-based magnetometry using an ensemble of nitrogen-vacancy color centers. This diamond-based technique that has both optical and magnetic detection modalities may be adapted for massively parallel screening of arrays of nanoscale samples.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.5125273

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