Enhanced photoluminescence from single nitrogen-vacancy defects in nanodiamonds coated with phenol-ionic complexes

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	Nanoscale
Authors	Kerem Bray, Rodolfo Previdi, Brant C. Gibson, Olga Shimoni, Igor Aharonovich
Institutions	University of Technology Sydney, RMIT University
Citations	30
Analysis	Full AI Review Included

Enhanced Photoluminescence from Single NV Defects in Nanodiamonds: A 6CCVD Analysis

This documentation analyzes the research demonstrating enhanced photoluminescence (PL) from Nitrogen-Vacancy (NV) centers in nanodiamonds (NDs) coated with metal-phenolic networks, presenting the critical technical specifications and linking them directly to 6CCVD’s specialized MPCVD material fabrication capabilities for advanced quantum and bio-sensing applications.

Executive Summary

This study successfully implemented a robust, scalable, and biocompatible surface functionalization technique to significantly enhance the optical performance of single NV defects in nanodiamonds (NDs) for bio-sensing and bio-imaging applications.

Photoluminescence Enhancement: A minimum of threefold increase in fluorescence intensity was achieved by coating 45 nm NDs with a metalo-phenolic network (Fe(III)-Tannic Acid complex).
Lifetime Reduction: The fluorescence lifetime was drastically reduced from an average of $\tau$ = 8.31 ns (pristine) to $\tau$ = 5.45 ns (coated), indicating an increase in the radiative decay rate and brighter emission.
Defect Stabilization: The enhancement mechanism is attributed to the suppression of non-radiative decay pathways, specifically surface charge traps, leading to improved quantum efficiency.
Quantum Integrity Maintained: The crucial Optically Detected Magnetic Resonance (ODMR) signal contrast and the single-photon emission properties (g⁽²⁾(t) < 0.5) were preserved after coating.
Biocompatibility and Scalability: The method utilizes non-toxic, FDA-recognized components and is a cost-effective, single-step self-assembly process suitable for functionalizing bulk quantities of nanodiamonds.
Core Application: Provides a versatile platform for highly sensitive probes in bio-labeling, high-resolution magnetometry, and quantum sensing.

Technical Specifications

The following table summarizes the key experimental parameters and performance metrics achieved in the photoluminescence enhancement of the NV centers.

Parameter	Value	Unit	Context
Nanodiamond Size (Tested)	45	nm	Used for single NV center measurements
PL Enhancement Factor	≥ 3 (Threefold)	-	Compared to pristine nanodiamonds
Pristine ND Lifetime ($\tau$)	8.31 ± 1.05	ns	Average decay time before coating
Coated ND Lifetime ($\tau$)	5.45 ± 1.49	ns	Average decay time after Fe(III)-TA coating
Excitation Wavelength	532	nm	Confocal microscope setup (continuous/pulsed)
Lifetime Measurement $\lambda$	514	nm	Picosecond laser diode
Numerical Aperture (NA)	0.9	-	High NA objective used for collection
NV Zero Phonon Line (ZPL)	637	nm	Visible emission peak in PL spectrum
ODMR Ground State Splitting	2.87	GHz	Characteristic magnetic resonance frequency
Zeta Potential Shift	-13.5 ± 4.8 to -25.4 ± 6.4	mV	Confirms successful metal-phenolic complex formation
EDS Accelerating Voltage	5	kV	Used for surface elemental mapping (Oxygen detection)
Coating Components	FeCl₃·6H₂O, Tannic Acid	-	Biocompatible precursors for metal-phenolic network

Key Methodologies

The study relies on a robust, one-step self-assembly process to create the metal-phenolic network (MPN) coating, enabling functionalization of bulk nanodiamond particles.

Nanodiamond Suspension Preparation:
- 500 µL of nanodiamond (NaBond) solution (0.5 mg/ml concentration) was suspended in MilliQ water.
Metal Ion Introduction (Fe(III)):
- 5 µL of 10 mg/mL FeCl₃·6H₂O solution was added under vigorous agitation.
Phenolic Ligand Introduction (TA):
- 5 µL of 40 mg/mL Tannic Acid (TA) solution was added, causing an immediate color change from clear to purple-grey.
pH Stabilization and Network Formation:
- 500 µL of a 3-(N-morpholino)propanesulfonic acid buffer was added, and the solution pH was adjusted to 7.4 to ensure stable network formation.
Purification and Isolation:
- The sample underwent two subsequent washing and centrifugation cycles (10,000 rcf for 10 min) using water to remove residual unreacted Fe(III) and TA.
Surface Characterization:
- Successful surface modification was confirmed by measuring a significant shift in Zeta potential (increase in negative charge) and verified by Energy-Dispersive X-ray Spectroscopy (EDS) mapping, showing high oxygen content on the coated NDs.

6CCVD Solutions & Capabilities

6CCVD provides the high-quality, ultra-pure MPCVD diamond necessary to serve as the foundational material for next-generation quantum and bio-sensing probes, matching or exceeding the requirements of this advanced research.

Applicable Materials

To replicate or extend this research, 6CCVD recommends precursor material that offers maximal control over defect placement and purity:

6CCVD Material	Relevance to Study	Key Advantage for Customers
High Purity Single Crystal Diamond (SCD)	Ideal precursor for nanodiamond milling or integrated devices.	Enables precise creation and control of NV centers (N concentration < 1 ppb possible) and minimizes unwanted non-radiative surface traps (the focus of the paper).
Optical Grade SCD Wafers	Suitable for integrating this surface chemistry approach into larger, flat devices.	Low birefringence, high surface quality (Ra < 1 nm), essential for integrated quantum photonics platforms like dielectric cavities (Ref. 17).
Boron-Doped Diamond (BDD)	Alternative material for electrochemical sensing applications.	BDD electrodes, customizable by 6CCVD, can be functionalized similarly for stable interfaces in biological media where sensing probes are often required.

Customization Potential and Engineering Services

6CCVD offers bespoke services critical for advancing both nanodiamond synthesis and the fabrication of integrated quantum devices:

Controlled Precursor Fabrication: We manufacture highly uniform SCD plates up to 125mm with thicknesses controlled from 0.1 µm up to 500 µm. These dimensions provide superior starting material for crushing and milling into highly mono-dispersed nanodiamonds with superior NV concentration control compared to commercially sourced powder.
Ultra-Low Defect Surfaces: The paper stresses the suppression of surface non-radiative channels. 6CCVD provides ultra-smooth polishing (Ra < 1 nm for SCD), minimizing surface defects before chemical processing, further enhancing the final quantum efficiency.
Integrated Device Metalization: For alternative enhancement methods (e.g., plasmonic coupling, Ref. 16), 6CCVD offers in-house custom metalization of diamond substrates using materials including Ti, Au, Pt, Pd, W, and Cu. This allows researchers to integrate quantum emitters directly with metallic nanostructures fabricated on a 6CCVD substrate.
Precision Machining: 6CCVD offers laser cutting and precise shaping services for diamond plates, enabling the fabrication of custom geometries (e.g., micro-pillars, photonic crystal structures) required for advanced quantum optics and integrated circuits.

Engineering Support

6CCVD’s in-house PhD engineering team possesses deep expertise in MPCVD growth parameters, NV center creation, and material science. We are ready to assist researchers and technical engineers in optimizing diamond precursor material selection for specific bio-sensing, magnetometry, and bio-labeling projects utilizing color centers. Our expertise ensures materials are tailored to meet rigorous quantum coherence and biocompatibility standards.

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

View Original Abstract

Fluorescent nanodiamonds are attracting major attention in the field of bio-sensing and bio-labeling. In this work we demonstrate a robust approach to achieve an encapsulation of individual nanodiamonds with phenol-ionic complexes that enhance the photoluminescence from single nitrogen vacancy (NV) centers. We show that single NV centres in the coated nanodiamonds also exhibit shorter lifetimes, opening another channel for high resolution sensing. We propose that the nanodiamond encapsulation reduces the non-radiative decay pathways of the NV color centers. Our results provide a versatile and assessable way to enhance photoluminescence from nanodiamond defects that can be used in a variety of sensing and imaging applications.

Tech Support

Original Source

DOI: https://doi.org/10.1039/c4nr07510b