Nafion and Multiwall Carbon Nanotube Modified Ultrananocrystalline Diamond Microelectrodes for Detection of Dopamine and Serotonin

At a Glance

Metadata	Details
Publication Date	2021-05-06
Journal	Micromachines
Authors	An‐Yi Chang, Shabnam Siddiqui, Prabhu U. Arumugam
Institutions	Louisiana Tech University, Louisiana State University in Shreveport
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Microelectrodes for Neurochemical Sensing

Executive Summary

This research successfully demonstrates the fabrication and characterization of highly sensitive and selective microelectrodes based on modified Boron-Doped Ultrananocrystalline Diamond (BDUNCD) for long-term neurochemical monitoring. The findings validate the superior performance of MPCVD diamond substrates in complex biological environments, directly aligning with 6CCVD’s core material offerings.

Material Validation: Boron-Doped Diamond (BDUNCD) was confirmed as an ideal substrate, offering superior chemical inertness, dimensional stability, and exceptional resistance to surface fouling compared to traditional carbon electrodes.
Performance Enhancement: Modification with a hybrid Nafion/Multiwall Carbon Nanotube (MWCNT) layer significantly boosted sensitivity, achieving 6.75 µA µM^-1 cm^-2 for Dopamine (DA)—a 166-fold increase over unmodified BDUNCD.
Ultra-Low Detection Limits: The modified electrodes achieved a Limit of Detection (LoD) for DA of 5.4 ± 0.40 nM, suitable for detecting sub-second-to-second changes in neurochemical levels expected in the brain.
High Selectivity: The Nafion layer effectively rejected common anionic interferents (Ascorbic Acid, AA), enabling clear, distinguishable detection of DA and Serotonin (5-HT) in complex ternary mixtures.
Long-Term Stability: The modified BDUNCD microelectrodes maintained signal stability and selectivity for up to 9 hours of continuous testing, addressing a critical challenge in chronic neurochemical recording.
Fabrication Expertise: The process relied on high-quality CVD diamond film growth, precision optical lithography for patterning, and advanced Electrophoretic Deposition (EPD) for functional coatings.

Technical Specifications

The following hard data points were extracted from the analysis of the Nafion-MWCNT-BDUNCD microelectrode performance:

Parameter	Value	Unit	Context
Diamond Material Type	BDUNCD	N/A	Boron-Doped Ultrananocrystalline Diamond
Diamond Film Thickness	2	µm	HFCVD deposited film
Diamond Resistivity	~0.08	Ω·cm	Low resistivity required for electrochemical activity
Diamond Roughness (Ra)	<10	nm rms	Ultra-smooth surface characteristic
Electrode Geometry	250	µm	Diameter of disk microelectrodes
MWCNT Coating Thickness	~200	nm	Applied via EPD
Nafion Coating Thickness	~50	nm	Applied via EPD
Dopamine (DA) Sensitivity	6.75	µA µM^-1 cm^-2	Nafion-MWCNT-BDUNCD (166-fold increase)
Serotonin (5-HT) Sensitivity	4.55	µA µM^-1 cm^-2	Nafion-MWCNT-BDUNCD (16-fold increase)
Limit of Detection (LoD, DA)	5.4 ± 0.40	nM	Achieved using droplet microfluidics
Response Time (DA)	2 ± 0.16	s	Fastest response time observed
Long-Term Stability	Up to 9	h	Distinguishable peaks maintained in ternary mixture
DA Oxidation Potential (Epa)	0.94 ± 0.01	V	Measured via FSCV

Key Methodologies

The fabrication and testing relied on precise material deposition and microfabrication techniques:

BDUNCD Film Growth: A 2 µm thick Boron-Doped Ultrananocrystalline Diamond (BDUNCD) film was deposited onto 4-inch silicon wafers (with a 1 µm SiO₂ layer) using a Hot Filament Chemical Vapor Deposition (HFCVD) process.
Microelectrode Patterning: Optical microlithography was used to define 3x3 arrays of individually addressable 250 µm diameter disk microelectrodes.
MWCNT Functionalization (EPD): Multiwall Carbon Nanotubes (MWCNTs) were selectively coated onto the BDUNCD working electrode using Electrophoretic Deposition (EPD). A stepwise voltage scan of -6 V was applied for 10 min, followed by curing at 70 °C, yielding a ~200 nm layer.
Nafion Functionalization (EPD): A 5 wt % Nafion solution was coated via EPD using a stepwise voltage scan of +0.5 V for 2 min, followed by curing at 70 °C, resulting in a ~50 nm layer.
Microfluidic Integration: A two-layer Polydimethylsiloxane (PDMS) microfluidic chip (100 µm and 65 µm layers) defining the microchannel was bonded to the BDUNCD microarray using oxygen plasma treatment (40 W for 20 s) to ensure excellent sealing.
Electrochemical Characterization: Differential Pulse Voltammetry (DPV) and Fast-Scan Cyclic Voltammetry (FSCV) were performed using a potentiostat in a two-electrode setup (BDUNCD working electrode vs. Pt microwire counter/reference) under controlled flow conditions (0.1 mL/min).

6CCVD Solutions & Capabilities

The successful development of high-performance neurochemical sensors hinges on the precise control of diamond material properties, geometry, and surface functionalization—all core competencies of 6CCVD.

Applicable Materials for Replication and Extension

The research utilized BDUNCD, a form of highly conductive, boron-doped polycrystalline diamond. 6CCVD provides the necessary foundational materials to replicate or advance this work:

Boron-Doped Polycrystalline Diamond (PCD/BDD): 6CCVD offers highly conductive BDD films, essential for achieving the low resistivity (~0.08 Ω·cm) required for high electrocatalytic activity. We can supply PCD/BDD wafers up to 125mm in diameter.
Thickness Control: The paper used a 2 µm thick film. 6CCVD specializes in precise thickness control for PCD/BDD films ranging from 0.1 µm up to 500 µm, allowing researchers to optimize film thickness for specific microelectrode capacitance and charge transfer kinetics.
Ultra-Smooth Substrates: The paper noted a roughness of Ra < 10 nm. 6CCVD guarantees polishing to Ra < 5 nm for inch-size PCD, providing an ideal, reproducible base for subsequent nanocoating via EPD or drop casting.

Customization Potential

6CCVD’s in-house fabrication capabilities directly address the complex geometric and surface requirements of this microelectrode array:

Research Requirement	6CCVD Customization Capability	Value Proposition
Custom Geometry	Precision laser cutting and patterning services.	We can supply the BDUNCD material pre-cut into custom chip sizes or patterned with the required 250 µm disk microelectrode arrays (3x3 or larger formats).
Metalization Layers	Internal capability for depositing Au, Pt, Pd, Ti, W, Cu.	The EPD process requires specific counter/reference electrodes (Pt, Ag/AgCl). We can integrate robust, lithographically defined Pt or Au contact pads and interconnects directly onto the diamond surface, ensuring stable electrical isolation and long-term performance.
Substrate Size	Plates/wafers up to 125mm (PCD).	Enables high-throughput microfabrication and scaling of the BDUNCD microelectrode arrays beyond the 4-inch wafers used in the study.
Dielectric Passivation	Expertise in depositing high-quality SiO₂ or other dielectric layers.	We ensure the integrity of the silicon dioxide passivation, critical for the electrical isolation of the individual microelectrode pads, as noted in the methodology.

Engineering Support

6CCVD’s in-house PhD material science team is available to assist researchers and engineers in replicating or extending this work in neurochemical sensing. We offer consultation on:

Optimizing Boron Doping: Tailoring the BDD film resistivity to maximize electron transfer rates while maintaining chemical stability.
Surface Preparation: Advising on pre-treatment protocols (e.g., hydrogen vs. oxygen termination) to optimize the adhesion and performance of subsequent functional coatings like MWCNT and Nafion.
Microfluidic Integration: Providing dimensionally stable diamond substrates that are compatible with PDMS bonding and high-pressure microfluidic flow cells.

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

View Original Abstract

Neurochemicals play a critical role in the function of the human brain in healthy and diseased states. Here, we have investigated three types of microelectrodes, namely boron-doped ultrananocrystalline diamond (BDUNCD), nafion-modified BDUNCD, and nafion-multi-walled carbon nanotube (MWCNT)-modified BDUNCD microelectrodes for long-term neurochemical detection. A ~50 nm-thick nafion-200-nm-thick MWCNT-modified BDUNCD microelectrode provided an excellent combination of sensitivity and selectivity for the detection of dopamine (DA; 6.75 μA μM−1 cm−2) and serotonin (5-HT; 4.55 μA μM−1 cm−2) in the presence of excess amounts of ascorbic acid (AA), the most common interferent. Surface stability studies employing droplet-based microfluidics demonstrate rapid response time (<2 s) and low limits of detection (5.4 ± 0.40 nM). Furthermore, we observed distinguishable DA and 5-HT current peaks in a ternary mixture during long-term stability studies (up to 9 h) with nafion-MWCNT-modified BDUNCD microelectrodes. Reduced fouling on the modified BDUNCD microelectrode surface offers significant advantages for their use in long-term neurochemical detection as compared to those of prior-art microelectrodes.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi12050523

References

2015 - Ventral striatal dopamine reflects behavioral and neural signatures of model-based control during sequential decision making [Crossref]
1962 - The pathogenesis of Parkinson’s disease: A new hypothesis
2015 - Jejunal Infusion of Levodopa-Carbidopa Intestinal Gel Versus Oral Administration of Levodopa-Carbidopa Tablets in Japanese Subjects with Advanced Parkinson’s Disease: Pharmacokinetics and Pilot Efficacy and Safety [Crossref]
2009 - Reward-learning and the novelty-seeking personality: A between- and within-subjects study of the effects of dopamine agonists on young Parkinson’s patients [Crossref]
1994 - Continuousin vivo monitoring of evoked dopamine release in the rat nucleus accumbens by amperometry [Crossref]
2012 - Technological Barriers in the Use of Electrochemical Microsensors and Microbiosensors for in vivo Analysis of Neurological Relevant Substances [Crossref]
2003 - Detecting Subsecond Dopamine Release with Fast-Scan Cyclic Voltammetry in Vivo [Crossref]
2017 - Hitchhiker’s Guide to Voltammetry: Acute and Chronic Electrodes for in Vivo Fast-Scan Cyclic Voltammetry [Crossref]
2011 - Carbon nanofiber electrode array for electrochemical detection of dopamine using fast scan cyclic voltammetry [Crossref]