Diamond as Insulation for Conductive Diamond—A Spotted Pattern Design for Miniaturized Disinfection Devices
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-08-18 |
| Journal | C – Journal of Carbon Research |
| Authors | Manuel Zulla, Vera Vierheilig, Maximilian Koch, Andreas Burkovski, Matthias Karl |
| Institutions | Friedrich-Alexander-Universität Erlangen-Nürnberg, Saarland University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research presents a novel, polymer-free Double Diamond Laminate (DDL) electrode design for highly miniaturized electrochemical disinfection devices, suitable for medical applications like root canal treatment.
- Core Innovation: The DDL consists of a conductive Boron-Doped Diamond (BDD) layer partially insulated by a non-conductive Undoped Diamond (UDD) layer, eliminating the need for potentially non-biocompatible polymeric insulators.
- Miniaturization Achieved: The prototype uses a 50 µm diameter Niobium wire, achieving an overall anode diameter of approximately 55 µm, designed to fit within fine medical cannulas (e.g., 31 gauge).
- Spotted Pattern Technique: Selective insulation was achieved using a Spotted Copper Deposition (SCD) intermediate layer, which inhibited UDD growth in specific areas, leaving approximately 80% of the BDD surface electrochemically active after copper removal.
- Microdistancing: The DDL structure minimizes the anode-cathode gap (UDD thickness) to 3-5 µm, significantly improving electrolytic efficiency and allowing Reactive Oxygen Species (ROS) production (e.g., H2O2) even in low-conductivity electrolytes (demineralized water).
- Performance: The DDL successfully produced H2O2 concentrations up to 30 mg/L at moderate voltages (15 V) and current densities (0.01-0.27 A/cm2), confirming its operational capability as a miniaturized flow reactor.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Diameter | 50 | µm | Niobium (Nb) wire |
| BDD Layer Thickness | 1-2 | µm | First coating (conductive anode) |
| UDD Layer Thickness | 3-4 | µm | Second coating (insulator) |
| Total DDL Diameter (Anode) | ~55 | µm | Insulated wire diameter |
| Anode-Cathode Gap (Minimum) | 3-5 | µm | UDD thickness (vs. 10 µm for polymer) |
| Target Cannula Outer Diameter | ~250 | µm | Required for root canal application |
| BDD Active Surface Area (Estimated) | ~80% (0.075 cm2) | % (cm2) | Area accessible to electrolyte |
| Operating Voltage Range | 5-15 | V | Applied potential for oxidant production |
| Operating Current Density | 0.01-0.27 | A/cm2 | Resulting current density |
| Maximum H2O2 Concentration | 30 | mg/L | Measured at 15 V, 20 mA |
| Electrolyte Conductivity (Test) | <50 | µS/cm | Demineralized water |
| BDD Band Gap | 5.47 | eV | At 300 K |
Key Methodologies
Section titled “Key Methodologies”The Double Diamond Laminate (DDL) was manufactured using a multi-step Hot-Filament Chemical Vapor Deposition (HFCVD) and electrochemical process sequence:
-
Conductive BDD Coating (Anode Layer):
- Substrate: 50 µm Niobium (Nb) wire.
- Process: HFCVD.
- Temperature/Pressure: Approximately 800 °C, 2 mbar.
- Duration: 6 hours.
- Gas Phase (Doping): H2 (1000 mL/min), CH4 (16 mL/min), Trimethyl Borate (TMB) (0.15 mL/min).
- Result: 1-2 µm thick conductive BDD layer.
-
Spotted Copper Deposition (SCD) (Intermediate Layer):
- Purpose: To selectively inhibit subsequent UDD growth, creating a spotted pattern.
- Setup: Simple galvanic cell (BDD-Nb wire as cathode, BDD-Nb sheets as anodes).
- Electrolyte: Copper (II) sulfate pentahydrate solution (20 g/L).
- Parameters: Current 50 mA, Voltage ~1.5 V, Duration 2-10 seconds.
- Result: Agglomerate-like copper precipitates, unevenly distributed, covering areas intended for insulation.
-
Non-Conductive UDD Coating (Insulation Layer):
- Process: HFCVD (analogous to BDD coating, but without dopant).
- Duration: 20 hours (final prototype, extended from 5-15 h tests).
- Gas Phase (Undoped): H2 (1000 mL/min), CH4 (16 mL/min).
- Result: 3-4 µm thick UDD layer grown over the BDD and copper spots. Copper inhibited dense diamond growth, resulting in porous/fissured UDD over those areas.
-
Copper Etching and Activation:
- Step 1 (Electrochemical Etching): Applied 10 V for 2 minutes in distilled water (DDL positively charged, BDD electrode negatively charged).
- Step 2 (Acidic Etching): Nitric acid (20%) and hypochlorous acid (20%) mixture (1:1 ratio), performed twice.
- Cleaning: Ultrasonic bath with distilled water between steps.
- Result: Copper removed, leaving karst cave-like structures and pores in the UDD layer, exposing the underlying BDD layer for electrochemical activity.
Commercial Applications
Section titled “Commercial Applications”This DDL technology leverages the robust chemical and mechanical properties of diamond combined with efficient in situ oxidant production, making it highly relevant for several specialized fields:
| Application Area | Specific Use Case | Technical Advantage |
|---|---|---|
| Medical Disinfection | Root Canal Treatment (Endodontics) | Miniaturized flow reactor (Ø ~55 µm) for localized, polymer-free disinfection using ROS (e.g., H2O2, hydroxyl radicals). |
| Medical Disinfection | Biofilm Removal (Dental Implants) | Robust, chemically inert BDD surface capable of generating strong oxidants to eliminate single and multi-resistant bacterial strains. |
| Medical Devices | Cannula-Based Flow Reactors | Integration of an oxidative component into standard medical cannulas (e.g., fine pen needles) for localized sterilization or treatment delivery. |
| Water Treatment (EAOP) | Micro-Scale Water Decontamination | Highly efficient electrochemical advanced oxidation processes (EAOP) enabled by the ultra-small anode-cathode gap (microdistancing), allowing operation in low-conductivity water. |
| Sensor Technology | Microelectrode Arrays | The DDL concept provides a foundation for creating robust, integrated all-diamond microelectrodes for sensing or synthesis applications where selective conductivity is required. |
View Original Abstract
Boron-doped diamond (BDD) electrodes are well known for the in situ production of strong oxidants. These antimicrobial agents are produced directly from water without the need of storage or stabilization. An in situ production of reactive oxygen species (ROS) used as antimicrobial agents has also been used in recently developed medical applications. Although BDD electrodes also produce ROS during water electrolysis, only a few medical applications have appeared in the literature to date. This is probably due to the difficulties in the miniaturization of BDD electrodes, while maintaining a stable and efficient electrolytic process in order to obtain a clinical applicability. In this attempt, a cannula-based electrode design was achieved by insulating the anodic diamond layer from a cathodic cannula, using a second layer of non-conducting diamond. The undoped diamond (UDD) layer was successfully grown in a spotted pattern, resulting in a perfectly insulated yet still functional BDD layer, which can operate as a miniaturized flow reactor for medical applications. The spotted pattern was achieved by introducing a partial copper layer on top of the BDD layer, which was subsequently removed after growing the undoped diamond layer via etching. The initial analytical observations showed promising results for further chemical and microbial investigations.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
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