Boron‐Doped Diamond Dual‐Plate Deep‐Microtrench Device for Generator‐Collector Sulfide Sensing
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2015-07-14 |
| Journal | Electroanalysis |
| Authors | Harriet M. Harvey, Andrew J. Gross, Paula Brooksby, Alison J. Downard, Stephen J. Green |
| Institutions | University of Bath, MacDiarmid Institute for Advanced Materials and Nanotechnology |
| Citations | 6 |
| Analysis | Full AI Review Included |
Technical Documentation: Boron-Doped Diamond Dual-Plate Microtrench Devices for Sulfide Sensing
Section titled “Technical Documentation: Boron-Doped Diamond Dual-Plate Microtrench Devices for Sulfide Sensing”Executive Summary
Section titled “Executive Summary”This study successfully validates the use of Boron-Doped Diamond (BDD) dual-plate microtrench electrodes for the electroanalytical detection of sulfide (HS⁻) in complex media, relevant to biological and environmental sensing.
- BDD Validation: Confirms BDD as a robust electrode material, capable of supporting generator-collector redox cycling for sulfide species, even in the challenging presence of ambient oxygen.
- Geometric Control: Microtrench geometry (specifically depth) is proven critical. A “deep” trench (180 µm) enables in situ oxygen removal in the upper region, creating the necessary anoxic conditions in the lower region for efficient sulfide redox cycling.
- Enhanced Sensitivity: The deep microtrench geometry amplified the sensor signal, allowing detection down to low micromolar (µM) levels, relevant for analyzing physiological hydrogen sulfide concentrations (up to ~60 µM in blood).
- Redox Mechanisms: Two distinct electrocatalytic processes were identified and utilized for sensing: a 2-electron oxidation process (at 0.0 V vs. SCE) and a 6-electron oxidation process (at 1.1 V vs. SCE).
- Protocol Reliability: The methodology was successfully verified using a standard addition protocol, achieving high accuracy in estimating an unknown 50 µM sulfide spike (estimated 45-54 µM).
- Future Pathway: This proof-of-principle demonstrates a viable route for highly selective, dual-electrode sensing in in situ biological applications, addressing the need for robust H₂S detection methods.
Technical Specifications
Section titled “Technical Specifications”Extracted parameters relating to the BDD material, device geometry, and electrochemical performance.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electrode Material | BDD on p-doped Si | N/A | Core CVD material |
| BDD Film Thickness | 300 | nm | Deposited layer specification |
| Boron Doping Concentration | 8000 | ppm | High-conductivity level |
| Resistivity | 10 | mΩ cm | Electrical performance metric |
| Electrode Dimensions (w × l) | 5 mm × 20 mm | mm | Substrate size |
| Inter-Electrode Gap (δ) | 6 | µm | Trench width, fixed |
| Shallow Microtrench Depth | 44 ± 4 | µm | Estimated by Nernst model |
| Deep Microtrench Depth | 180 ± 20 | µm | Estimated by Nernst model |
| Collector Potential (O₂ Removal) | -1.4 | V vs. SCE | Fixed potential for anoxic zone creation |
| Generator Potential (2-e⁻ Process) | 0.0 | V vs. SCE | Sulfide oxidation (HS⁻ → S⁰) |
| Generator Potential (6-e⁻ Process) | 1.1 | V vs. SCE | Sulfide oxidation (HS⁻ → SO₃2-) |
| Scan Rate (Voltammetry) | 100 | mVs⁻¹ | Electrochemical measurement speed |
| Target Sensing Concentration | ~60 | µM | Relevant physiological level (blood) |
| Diffusion Coefficient (HS⁻) | 1.6 × 10-9 | m2s⁻¹ | Used for theoretical slope calculation |
Key Methodologies
Section titled “Key Methodologies”The following recipe parameters and fabrication steps were crucial to the successful creation and operation of the BDD dual-plate microtrench device:
- BDD Substrate Sourcing: Utilized 5 mm × 20 mm BDD-coated p-doped Si substrates with a specific 300 nm BDD thickness, 8000 ppm doping, and 10 mΩ cm resistivity.
- Contact Application: A 5 mm² active area was defined using silicone application (Silcoset 151). Electrical contacts were made using conducting copper tape (RS).
- Insulating Layer Application: Two BDD substrates were masked with Kapton tape for electrical contact areas, then spin-coated with SU-8 2002 photoresist using a two-step process (500 rpm for 15 seconds, then 3000 rpm for 30 seconds).
- Assembly and Curing: The masked and coated substrates were pressed together face-to-face and cured on a hot plate, starting at 90 °C for 2 minutes and ramping up to 160 °C for 5 minutes.
- Microtrench Definition and Polishing: The electrode end was sliced off using a diamond cutter (Isomet 1000) and polished flat with SiC abrasive paper to define the trench opening.
- Trench Etching: The SU-8 photoresist layer separating the plates was partially etched using piranha solution (5:1 sulfuric acid: hydrogen peroxide) to create the defined microtrench geometry (depths of 44 µm and 180 µm, with a 6 µm gap).
- Electrochemical Setup: Measurements were performed at 20 ± 2 °C using a bipotentiostat system, utilizing a platinum wire counter electrode and a Saturated Calomel Electrode (SCE) reference.
- Electrolyte Composition: Testing employed 20 mM phosphate buffer (pH 8), 0.1 M KNO₃ supporting electrolyte, and 4 mM Kolliphor®EL as a sulfur solubilizing agent.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The successful detection of sulfide using BDD dual-plate microtrench devices opens significant possibilities in biomedical and environmental sensing. 6CCVD provides the specialized CVD diamond materials and precision engineering services necessary to replicate, optimize, and scale this technology.
Applicable Materials: High-Purity Boron-Doped Diamond (BDD)
Section titled “Applicable Materials: High-Purity Boron-Doped Diamond (BDD)”To match or exceed the performance seen in this research, 6CCVD recommends:
- Heavy Boron-Doped PCD/SCD Wafers: We offer MPCVD BDD films with custom doping levels, capable of achieving the high conductivity required (matching or better than 10 mΩ cm) for efficient generator and collector operation.
- Custom Thickness BDD: While the paper used a 300 nm film, 6CCVD provides BDD layers up to 500 µm thick, allowing for bulk BDD devices or superior durability when coated on substrates like silicon.
- Substrate Compatibility: We supply BDD films deposited on high-quality Si substrates, ensuring compatibility with standard semiconductor fabrication processes required for microtrench design replication.
Customization Potential: Precision Microtrench Engineering
Section titled “Customization Potential: Precision Microtrench Engineering”Replicating the microtrench requires highly accurate cutting, polishing, and geometry control. 6CCVD’s advanced engineering services directly address the geometric challenges identified in the research:
| Research Requirement | 6CCVD Capability & Advantage |
|---|---|
| Specific Dimensions (5 mm x 20 mm) | Custom Dimensions: We provide laser cutting and precision machining services to shape BDD plates and wafers up to 125 mm in diameter, ensuring exact dimensions for dual-plate assembly. |
| Trench Depth Control (180 µm) | Advanced Etching: We employ deep reactive ion etching (DRIE) and other proprietary plasma etching techniques, offering superior control and repeatability over the deep microtrench geometry compared to the aggressive wet chemical etching (piranha solution) used in the paper. |
| Inter-Electrode Gap (6 µm) | High-Precision Polishing: Our polishing services achieve surface roughness down to Ra < 5 nm (PCD) or Ra < 1 nm (SCD), critical for achieving the extremely tight, consistent 6 µm gap separation necessary for maximum feedback amplification (Nernst diffusion). |
| Potential Metalization Needs | In-House Metalization: Should future designs require integrated contact pads or metal seals (e.g., Ti/Pt/Au contacts for robust bonding), 6CCVD offers full internal metalization capabilities. |
Engineering Support & Application Development
Section titled “Engineering Support & Application Development”The conclusion of the paper explicitly calls for further work exploring geometry optimization (smaller gaps, deeper trenches) and tackling interference from biological matrices.
- Geometry Optimization: 6CCVD’s in-house PhD engineering team specializes in diamond electrochemistry and CVD material optimization. We offer consultation and prototyping support for defining optimal microtrench geometry parameters to maximize signal amplification and minimize background noise for specific [Sulfide Sensing in Serum] projects.
- Scale and Reproducibility: We provide material solutions optimized for high reproducibility across a large set of devices, facilitating the transition from exploratory proof-of-principle studies to clinical or industrial sensing applications.
- Global Supply Chain: Benefit from reliable global shipping (DDU default, DDP available) for time-sensitive research and development projects worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract A BDD‐BDD dual‐plate microtrench electrode with 6 μm inter‐electrode spacing is investigated using generator‐collector electrochemistry and shown to give microtrench depth‐dependent sulfide detection down to the μM levels. The effect of the microtrench depth is compared for a “shallow” 44 μm and a “deep” 180 μm microtrench and linked to the reduction of oxygen to hydrogen peroxide which interferes with sulfide redox cycling. With a deeper microtrench and a fixed collector potential at −1.4 V vs. SCE, two distinct redox cycling potential domains are observed at 0.0 V vs. SCE (2‐electron) and at 1.1 V vs. SCE (6‐electron).