A Diamond-Based Electrode for Detection of Neurochemicals in the Human Brain

At a Glance

Metadata	Details
Publication Date	2016-03-14
Journal	Frontiers in Human Neuroscience
Authors	Kevin E. Bennet, Jonathan R. Tomshine, Hoon‐Ki Min, Felicia Manciu, Michael P. Marsh
Institutions	The University of Texas at El Paso, Deakin University
Citations	100
Analysis	Full AI Review Included

Technical Documentation: Boron-Doped Diamond Electrodes for Chronic Neurochemical Sensing

This document analyzes the requirements and findings of the research paper “A Diamond-Based Electrode for Detection of Neurochemicals in the Human Brain” and aligns them with 6CCVD’s advanced MPCVD diamond capabilities, focusing on solutions for chronic implantation and closed-loop Deep Brain Stimulation (DBS) systems.

Executive Summary

The research validates Boron-Doped Diamond (BDD) microelectrodes as the superior material for chronic, implantable neurochemical sensing using Fast-Scan Cyclic Voltammetry (FSCV) in human Deep Brain Stimulation (DBS) applications.

Longevity Superiority: BDD electrodes retained 83.9% of their initial dopamine sensitivity after 144 hours (5.2 million continuous FSCV cycles), whereas standard Carbon Fiber Microelectrodes (CFMs) were rendered completely insensitive (89.4% degradation).
Mechanical Robustness: BDD electrodes demonstrated a physical robustness improvement of >2 orders-of-magnitude compared to CFMs, withstanding forces of 30-40 g (vs. 0.1-0.15 g for CFMs) without catastrophic failure, a critical factor for chronic implantation safety.
Electrochemical Performance: BDD successfully detected distinct in vivo adenosine-like signatures in the human thalamus (VIM/STN) during DBS surgery, confirming efficacy in a complex biochemical environment.
Material Specification: The electrodes utilized Polycrystalline BDD films (0.5-2 µm crystal size, 5-10 µm thickness) deposited via Chemical Vapor Deposition (CVD) onto tungsten substrates.
Application Focus: This work establishes BDD as the enabling technology for next-generation, closed-loop “smart” DBS devices requiring long-term, stable neurochemical feedback.

Technical Specifications

Parameter	Value	Unit	Context
Crystal Dimension (Average)	0.5 - 2	µm	Polycrystalline BDD film
Film Thickness	5 - 10	µm	BDD layer on tungsten substrate
Electrode Tip Diameter	~50	µm	Conical tip diameter
Exposed Length	~100	µm	Sensing surface length
Geometric Surface Area	~10,000	µm²	Total exposed sensing area
CVD Filament Temperature	2000	°C	Nominal Hot-Filament CVD (HFCVD)
CVD Total Pressure	20	torr	HFCVD growth environment
Dopant Concentration (TMB)	1000	ppm	Trimethylborane in H₂ source gas
FSCV Voltage Range	-0.4 to +1.5	V	Triangular waveform applied
FSCV Scan Rate	400	V/s	Rate of potential change
FSCV Frequency	10	Hz	Continuous measurement frequency
Longevity (144h/5.2M cycles)	16.1	% Decrease	BDD dopamine sensitivity degradation
Mechanical Robustness Ratio	200	x	BDD force resistance relative to CFM failure

Key Methodologies

The diamond electrodes were fabricated using custom Hot-Filament Chemical Vapor Deposition (HFCVD) techniques, followed by precise insulation and exposure steps.

Substrate Preparation: Tungsten wires (250 µm diameter) were electrochemically etched in 1 M sodium hydroxide using 10 V AC voltage to create a tapered, sharpened tip.
Seeding: Tungsten tips were sonicated with 100 nm diamond particles suspended in isopropyl alcohol to promote nucleation.
CVD Growth: Boron-doped polycrystalline diamond films were deposited using HFCVD with a source gas mixture of 1% Methane (CH₄) in Hydrogen (H₂). Trimethylborane (TMB) at 1000 ppm in H₂ served as the boron dopant source.
CVD Parameters: Filament temperature was maintained at 2000 °C, total pressure at 20 torr, with the substrate positioned 8-10 mm from the hot filament.
Insulation: A Parylene-C coating (~30 µm thickness) was applied via low-pressure polymerization to insulate the shaft and enhance biocompatibility.
Sensing Tip Exposure: A pulsed ultraviolet laser was used to selectively ablate the Parylene coating, exposing the final ~100 µm of the BDD film at the electrode tip for sensing.
Electrochemical Testing (FSCV): Electrodes were calibrated and tested using a triangular voltage waveform (-0.4 V to +1.5 V) at a 400 V/s scan rate and 10 Hz frequency for continuous longevity trials.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and custom fabrication services required to replicate and extend this critical research into chronic neurochemical sensing and closed-loop DBS systems.

Applicable Materials

The core requirement of this research is a highly conductive, robust, and electrochemically stable diamond film.

Heavy Boron Doped Polycrystalline Diamond (BDD-PCD): 6CCVD specializes in high-quality BDD films grown via MPCVD, offering the precise boron incorporation necessary for the wide potential window and low baseline current critical for FSCV. Our PCD material is ideal for achieving the mechanical robustness (30-40 g force resistance) demonstrated in the study.
Custom SCD/PCD Plates: While the paper used micro-rods, 6CCVD can supply BDD material in plate or wafer form (up to 125mm PCD) for subsequent microfabrication, etching, or integration into complex multi-electrode arrays.

Customization Potential

The success of the diamond electrode relies on precise geometry and integration with the tungsten substrate. 6CCVD offers the following services to meet these specific engineering demands:

Requirement from Paper	6CCVD Capability	Benefit to Researcher
Custom Substrate Handling	Capability to deposit BDD films on various substrates, including Tungsten (W), Silicon, and specialized alloys.	Enables direct replication of the tungsten rod electrode design for high mechanical strength.
Precise Film Thickness	SCD/PCD thickness control from 0.1 µm up to 500 µm.	Allows precise control over the 5-10 µm BDD film thickness required for optimal electrochemical performance and adhesion.
Micro-Feature Fabrication	Advanced laser cutting and etching services.	Facilitates the creation of complex micro-scale geometries (e.g., 50 µm tip diameter, 100 µm exposed length) and integration into flexible leads.
Custom Metalization	In-house deposition of Au, Pt, Pd, Ti, W, and Cu.	Essential for creating robust electrical contacts and reference electrodes required for the WINCS system integration.
Polishing Requirements	Polishing services achieving Ra < 5 nm for inch-size PCD.	Ensures smooth, uniform surfaces for consistent electrochemical activity and reduced fouling in biological environments.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers can provide expert consultation on material selection, doping levels, and fabrication processes required for chronic neurochemical sensing and closed-loop DBS projects. We assist researchers in optimizing BDD film properties (e.g., crystal size, sp² content) to maximize sensitivity and longevity for specific analytes (Dopamine, Adenosine, Serotonin).

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

View Original Abstract

Deep brain stimulation (DBS), a surgical technique to treat certain neurologic and psychiatric conditions, relies on pre-determined stimulation parameters in an open-loop configuration. The major advancement in DBS devices is a closed-loop system that uses neurophysiologic feedback to dynamically adjust stimulation frequency and amplitude. Stimulation-driven neurochemical release can be measured by fast-scan cyclic voltammetry (FSCV), but existing FSCV electrodes rely on carbon fiber, which degrades quickly during use and is therefore unsuitable for chronic neurochemical recording. To address this issue, we developed durable, synthetic boron-doped diamond-based electrodes capable of measuring neurochemical release in humans. Compared to carbon fiber electrodes, they were more than two orders-of-magnitude more physically-robust and demonstrated longevity in vitro without deterioration. Applied for the first time in humans, diamond electrode recordings from thalamic targets in patients (n = 4) undergoing DBS for tremor produced signals consistent with adenosine release at a sensitivity comparable to carbon fiber electrodes. (Clinical trials # NCT01705301).

Tech Support

Original Source

DOI: https://doi.org/10.3389/fnhum.2016.00102

References

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