A detailed EIS study of boron doped diamond electrodes decorated with gold nanoparticles for high sensitivity mercury detection

At a Glance

Metadata	Details
Publication Date	2021-05-04
Journal	Scientific Reports
Authors	Maeve McLaughlin, Alexander C. Pakpour‐Tabrizi, Richard B. Jackman
Institutions	London Centre for Nanotechnology, University College London
Citations	17
Analysis	Full AI Review Included

Executive Summary

This technical documentation analyzes the application of heavily Boron-Doped Diamond (BDD) electrodes for high-sensitivity mercury detection, focusing on the enhancements provided by gold nanoparticle (AuNP) decoration.

Core Achievement: Demonstrated that decorating BDD and polished BDD (pBDD) electrodes with 30 nm AuNPs significantly improves electrochemical sensitivity for mercury detection via Electrochemical Impedance Spectroscopy (EIS).
Performance Metric: AuNP-decorated electrodes exhibited lower effective capacitance ($C_{eff}$) and higher electron transfer rates ($k_0$) compared to bare BDD, indicating superior reactivity and lower detection limits.
Material Optimization: The study utilized heavily doped BDD ([B] > 10²⁰ cm^-3) grown via MPCVD, confirming its suitability as a robust, chemically stable electrode material for harsh environments.
Surface Influence: Polished pBDD (R_A ~ 50 nm) showed higher surface sp² carbon content than unpolished BDD (R_A ~ 50 µm), which became the dominant factor influencing sensitivity at high mercury concentrations (> 500 µM).
Catalytic Role of AuNPs: AuNPs act catalytically, aiding the pre-concentration of mercury ions from the bulk electrolyte onto the diamond surface, thereby improving detection efficiency at trace levels (down to 1 pM).
Commercial Potential: The exceptional capacitance values and robust performance confirm BDD electrodes, particularly when AuNP-decorated, are ideal for developing commercial, portable mercury sensors for aquatic environments.

Technical Specifications

The following hard data points were extracted from the experimental results, focusing on material properties and electrochemical performance at 1 pM Hg concentration.

Parameter	Value	Unit	Context
Boron Doping Concentration	> 10²⁰	cm^-3	Heavily doped, quasi-metallic conductivity
BDD Substrate Dimensions	10 x 10 x 0.5	mm	Unpolished polycrystalline BDD
pBDD Substrate Dimensions	10 x 10 x 0.4	mm	Mechanically polished polycrystalline BDD
Unpolished Roughness (BDD)	~ 50	µm	Surface roughness R_A
Polished Roughness (pBDD)	~ 50	nm	Surface roughness R_A
AuNP Average Diameter	30 ± 14	nm	On BDD substrate
AuNP Average Diameter	30 ± 11	nm	On pBDD substrate
Hg Concentration Range Tested	1 pM to 1	mM	Range for EIS measurements
Deposition Potential (SWASV)	0.35	V	Potential used for Hg pre-concentration
Stripping Potential (SWASV)	1.0	V	Potential used to strip Hg from surface
EIS Frequency Range	50 kHz to 50	MHz	Measurement range
Electron Transfer Rate ($k_0$)	0.67 ± 0.03	cm s^-1	BDD + AuNP (Open Circuit, 1 pM Hg)
Electron Transfer Rate ($k_0$)	1.24 ± 0.03	cm s^-1	pBDD + AuNP (Open Circuit, 1 pM Hg)
Effective Capacitance ($C_{eff}$)	0.36	µF/cm²	BDD + AuNP (0 M control)
Effective Capacitance ($C_{eff}$)	0.50	µF/cm²	pBDD + AuNP (0 M control)

Key Methodologies

The experiment utilized MPCVD-grown BDD substrates and a multi-step surface modification process followed by detailed EIS analysis.

Substrate Acquisition: Electrochemical grade BDD and pBDD substrates (10 x 10 mm) were sourced, featuring heavy Boron doping (> 10²⁰ cm^-3).
Organic Cleaning: Substrates underwent a ‘Piranha’ clean (3:1 v/v of 98% HCl and 30% H₂O₂) for 10 minutes to remove organic contaminants.
Hydrogen Termination: Surfaces were hydrogen-terminated using H-plasma in an MPCVD reactor (700 °C platen temperature, 800 W power, 40 Torr pressure) for 10 minutes to enhance AuNP adherence.
Gold Film Deposition: A non-continuous 5 nm gold film was sputtered onto the substrates using an Emscope SC500 sputter coater.
AuNP Formation: The gold films were segregated into 30 nm AuNPs via an annealing process (‘de-wetting’) in a Rapid Thermal Processing System (400 °C for 5 minutes) under nitrogen atmosphere.
Electrochemical Setup: A three-electrode setup was used (BDD working electrode, Ag/AgCl KCL reference electrode, platinum counter electrode) in a 0.1 M HNO₃ electrolyte.
EIS Measurement: EIS was performed over 50 kHz to 50 MHz (10 mV amplitude) at three key potentials (Open Circuit, 0.35 V deposition, 1.0 V stripping) across a mercury concentration range of 1 pM to 1 mM.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond materials and custom fabrication services required to replicate, scale, and advance this high-sensitivity sensor research.

Applicable Materials

To achieve the high sensitivity and robust performance demonstrated in this study, researchers require heavily doped, high-quality polycrystalline diamond.

6CCVD Material Recommendation	Specification Match	Rationale for Selection
Heavy Boron-Doped PCD	[B] > 10²⁰ cm^-3	Essential for quasi-metallic conductivity and wide electrochemical window required for SWASV/EIS.
Polished PCD Substrates	R_A < 5 nm (Inch-size)	6CCVD offers polishing far superior to the R_A ~ 50 nm used in the paper, minimizing surface sp² content and maximizing sp³ quality for enhanced electrochemical stability.
Custom Thickness PCD	0.1 µm to 500 µm	We can supply the exact 0.4 mm (400 µm) and 0.5 mm (500 µm) thicknesses used, or thinner films for integration into micro-sensor arrays.

Customization Potential

The research utilized specific dimensions and required precise metalization and surface preparation steps. 6CCVD offers comprehensive services to meet these exact engineering needs:

Custom Dimensions: While the paper used 10 x 10 mm samples, 6CCVD can supply PCD plates/wafers up to 125 mm in diameter, enabling large-scale sensor array fabrication or commercial production scaling.
Advanced Polishing: We provide ultra-smooth polishing (R_A < 5 nm for PCD) which is critical for minimizing the detrimental effects of surface sp² carbon, especially important for high-concentration detection (> 500 µM Hg).
Integrated Metalization: The study required a 5 nm Au film precursor. 6CCVD offers in-house metalization capabilities including Au, Pt, Pd, Ti, W, and Cu. We can deposit the necessary thin film stacks directly onto the BDD surface, streamlining the fabrication process for AuNP decoration or direct electrode contact.
Laser Cutting and Shaping: We provide precision laser cutting services to produce custom electrode shapes or complex geometries required for integration into portable sensor devices.

Engineering Support

The successful replication and extension of this high-sensitivity mercury detection method rely on precise control over diamond doping, surface termination (H-plasma), and metal deposition.

6CCVD’s in-house PhD team specializes in MPCVD diamond growth and surface engineering. We can assist researchers and engineers with:

Material Selection: Consulting on the optimal balance between doping density and surface roughness for specific trace metal detection limits.
Surface Preparation Protocols: Advising on the necessary Piranha cleaning and H-termination recipes to ensure strong catalytic AuNP adherence, maximizing the electron transfer rate ($k_0$).
Scaling and Integration: Providing technical guidance for transitioning from lab-scale 10 x 10 mm electrodes to larger, integrated commercial Heavy Metal Sensor platforms.

Call to Action

The exceptional performance of MPCVD BDD electrodes for high-sensitivity mercury detection highlights the need for reliable, high-quality diamond substrates. 6CCVD is the trusted global supplier for engineers and scientists requiring custom diamond solutions.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-021-89045-2