Quantum Sensing of Lanthandie Binding Tags with Relaxometer of NV Center in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-05-06 |
| Journal | Advanced Optical Materials |
| Authors | Zibo Gao, Zhengzhi Jiang, Qiyu Liang, Ruihua He, Van Cuong |
| Institutions | National University of Singapore, Jilin University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis outlines the development and validation of a highly sensitive quantum sensing platform utilizing Nitrogen-Vacancy (NV) centers in diamond for biomolecule detection.
- Core Technology: A relaxometer based on ensemble NV centers measures changes in the T1 spin relaxation time, which is perturbed by the strong magnetic noise generated by Gadolinium (Gd3+) ions.
- Probe System: Lanthanide Binding Tags (LBTs), fused with a specific nanobody, are loaded with Gd3+ and used as magnetic probes to target specific biomolecules.
- Key Achievement (Sensitivity): The system demonstrated a detection limit for the LBTs themselves of 25 fmol.
- Biomarker Detection: The platform was successfully applied to detect the Receptor-Binding Domain (RBD) of the SARS-CoV-2 spike protein using an immunomagnetic sandwich assay.
- Detection Threshold: The detection threshold for the RBD target protein reached approximately 1 pmol, surpassing the sensitivity of most optical lanthanide-based methods.
- Advantages: The method offers low cost, high sensitivity, and is inherently free from background fluorescence noise, providing a robust alternative to conventional optical biosensing.
- Adaptability: The technique is readily adaptable for detecting diverse protein targets by simply swapping the functionalization antibody and the LBT-nanobody probe.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| LBT Detection Limit | 25 | fmol | Magnetic detection capability validation. |
| RBD Protein Detection Limit | ~1 | pmol | Immunomagnetic assay threshold. |
| NV Center Zero Field Splitting (D) | ~2.87 | GHz | Energy gap between ms=0 and ms=±1 states. |
| Baseline T1 Relaxation Time | 3.02 | ms | Silanized diamond surface (0 fmol LBTs reference). |
| T1 Relaxation Time (73.5 fmol LBTs) | 0.77 | ms | Significant reduction due to Gd3+ adsorption. |
| T1-RBD Concentration Slope | -0.05 ± 0.0015 | ms/pmol | Linear relationship observed in the assay. |
| Nanobody Dissociation Constant (RBD) | 1.86 | nM | High affinity of the LBT-nanobody probe. |
| Diamond Pickling Temperature | 210 | °C | Cleaning and surface preparation (8 hours). |
| Piranha Hydroxylation Temperature | 75 | °C | Surface hydroxylation (45 minutes). |
| Diamond Silanization Temperature | 50 | °C | Incubation with APTES/Toluene (16 hours). |
| GdCl3 Concentration (LBT loading) | 2 | mM | Buffer concentration for Gd3+ binding. |
Key Methodologies
Section titled âKey MethodologiesâThe detection scheme relies on precise diamond surface engineering and a multi-step immunomagnetic assay:
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Diamond Surface Cleaning and Hydroxylation:
- Diamond is cleaned in 2M NaOH (ultrasonic) followed by pickling in 1:1 H2SO4/HNO3 at 210 °C for 8 hours.
- Hydroxylation is performed using Piranha solution (3:1 H2SO4/H2O2) at 75 °C for 45 minutes.
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Surface Silanization:
- The hydroxylated diamond is incubated in a solution of 2% 3-Aminopropyltriethoxysilane (APTES) in 98% toluene at 50 °C for 16 hours to introduce amine (NH2) functional groups.
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Probe Preparation (Gd3+ Loading):
- The LBT-nanobody fusion protein is mixed with 2 mM GdCl3 buffer and vortexed for 1 minute.
- The resulting Gd3+-LBT precipitate is washed three times with PBS buffer to remove unbound Gd3+ ions.
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Immunomagnetic Assay (Sandwich Structure Formation):
- Step 1 (Capture Antibody): Primary RBD polyclonal antibodies are immobilized onto the silanized diamond surface.
- Step 2 (Passivation): Bovine Serum Albumin (BSA) is applied to block unbound sites, preventing non-specific adsorption.
- Step 3 (Target Binding): The purified RBD target protein solution is introduced and incubated.
- Step 4 (Probe Binding): The Gd3+-containing LBTs (fused with anti-RBD nanobody) are introduced, forming the final antibody-RBD-LBT sandwich structure.
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Quantum Measurement:
- The diamond is placed in the NV relaxometer setup.
- The T1 relaxation time is measured using a sequence of green laser pulses (for initialization) and microwave pulses (for population shifting) to quantify the magnetic noise generated by the bound Gd3+ ions.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a robust platform for advanced biosensing and quantum measurement, relevant to several high-tech sectors:
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Medical Diagnostics and Clinical Research:
- Development of highly sensitive, rapid, and low-cost diagnostic tests for viral proteins (e.g., SARS-CoV-2) and other disease biomarkers.
- Platforms for detecting trace amounts of proteins in complex biological fluids without interference from background fluorescence.
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Quantum Sensing and Metrology:
- Advancement of room-temperature, solid-state quantum sensors based on NV centers for detecting ultra-small magnetic fields and magnetic noise in biological environments.
- Integration of NV relaxometry into portable or benchtop devices for chemical and biological analysis.
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Drug Discovery and Proteomics:
- High-throughput screening systems for analyzing protein-ligand binding kinetics and affinity using magnetic tags.
- Tools for studying biomolecular interactions where traditional optical methods lack sensitivity or specificity.
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Materials Science and Surface Engineering:
- Protocols for precise chemical functionalization (silanization, hydroxylation) of diamond and other wide-bandgap semiconductor surfaces for biosensor integration.
- Development of nanodiamond-based sensors for enhanced surface-to-volume ratio and improved sensitivity.
View Original Abstract
Abstract Lanthanide binding tags (LBTs) stand out as a prominent group of fluorescent probes that are extensively utilized in biological detection. However, research on LBTs has predominantly emphasized their fluorescence properties, which frequently compromised by background fluorescence noise. Investigating magnetic properties could optimize detection methodologies that offer enhanced sensitivity and specificity. This study measures the response of a relaxometer based on ensemble nitrogenâvacancy (NV) centers in diamond to various amounts of LBTs with gadolinium ions, determining the detection limit of LBTs to be 25 fmol. A detection scheme employing the NV relaxometer to detect specific binding between LBTs and target is then proposed and demonstrated. Specifically, the study assesses the relaxometerâs response to various concentrations of the interaction between the modified LBTs and ReceptorâBinding Domain (RBD) of SARSâCOVIDâ2 spike protein, with the detection threshold reaching â2 pmol. The research provides a potential application platform for biomarker detection under picomole concentration by using NV centers to detect the magnetism of LBTs.