A FLEXIBLE, LARGE-SCALE DIAMOND-POLYMER CHEMICAL SENSOR FOR NEUROTRANSMITTER DETECTION

At a Glance

Metadata	Details
Publication Date	2016-05-26
Journal	2016 Solid-State, Actuators, and Microsystems Workshop Technical Digest
Authors	Bin Fan, Yuhong Zhu, Robert Rechenberg, Martin Becker, W. Li
Institutions	Michigan State University, Fraunhofer USA
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Flexible BDD Neurotransmitter Sensor

This document analyzes the research paper, “A FLEXIBLE, LARGE-SCALE DIAMOND-POLYMER CHEMICAL SENSOR FOR NEUROTRANSMITTER DETECTION,” to provide technical specifications and demonstrate how 6CCVD’s advanced MPCVD diamond materials and customization services can support and extend this critical research in flexible bioelectronics.

Executive Summary

This research successfully demonstrates a flexible, high-performance electrochemical sensor utilizing Boron-Doped Polycrystalline Diamond (BDD) transferred onto a Parylene-C substrate for neurotransmitter detection (Dopamine, DA).

Core Achievement: Fabrication of a flexible, large-scale (4mm x 4.7mm) BDD three-electrode sensor system (WE, CE, RE).
Material Advantage: BDD provides a wide aqueous potential window and exceptionally low background current compared to traditional Au or Pt electrodes, crucial for high signal-to-noise ratio in bio-sensing.
Process Innovation: An improved wafer transfer technique using Deep Reactive-Ion Etching (DRIE) replaced wet KOH etching, resulting in superior BDD film uniformity, strong adhesion, and high yield onto the flexible Parylene substrate.
Mechanical Reliability: The BDD-Parylene bond, reinforced by Parylene anchors, was validated using a “Scotch tape” test, showing no delamination after five cycles of attachment and peeling.
High Sensitivity: The sensor achieved a sensitivity of 0.0012 µA/mm²·µM for Dopamine (DA) detection via chronoamperometry, confirming its utility for real-time physiological monitoring.
Material Specification: The sensor utilized a microcrystalline BDD film approximately 2.7 µm thick, synthesized via Microwave Plasma Assisted Chemical Vapor Deposition (MPACVD).

Technical Specifications

The following hard data points were extracted from the research paper detailing the material properties and electrochemical performance of the flexible BDD sensor.

Parameter	Value	Unit	Context
BDD Film Thickness	~2.7	µm	Microcrystalline BDD layer
Sacrificial Layer Thickness	1	µm	PECVD SiO₂ layer
Sensor Dimensions	4 x 4.7	mm	Overall design size
Working Electrode (WE) Area	0.8	mm²	Effective surface area
Counter/Reference Electrode (CE/RE) Area	0.48	mm²	Effective surface area
BDD Synthesis Temperature Range	500 - 900	°C	Typical MPACVD range
Aqueous Potential Window (BDD)	2.27 to 3.3	V	Literature range cited
Ru(NH₃)₆²⁺/³⁺ Sensitivity (CV)	0.018	mA/mm²·mM	Cathodic peak current
Dopamine (DA) Sensitivity (Chronoamperometry)	0.0012	µA/mm²·µM	Background corrected current
BDD Raman Peak (Diamond)	1327	cm⁻¹	Characteristic diamond band
BDD Raman Peaks (Boron)	505, 1209	cm⁻¹	Indicates heavy boron incorporation
Ru(NH₃)₆²⁺/³⁺ Peak Separation	~400	mV	Observed CV peak separation

Key Methodologies

The fabrication process relied on precise thin-film deposition, advanced lithography, and high-control etching techniques, all of which are supported by 6CCVD’s material expertise.

Sacrificial Layer Deposition: 1 µm SiO₂ was deposited onto a 3-inch Si wafer using PECVD.
BDD Synthesis: A ~2.7 µm microcrystalline BDD film was grown using a custom MPACVD reactor with a gas mixture of hydrogen, diborane, and methane.
Hard Mask & Patterning: A 1.3 µm Aluminum (Al) hard mask was sputtered, patterned via UV photolithography, and etched.
BDD Etching: The BDD film was patterned using plasma etching (ECR-RIE) with SF₆/Ar/O₂ processing gases.
Anchor Creation: Buffered Oxide Etchant (BOE) was used to over-etch the SiO₂ sacrificial layer, creating undercuts for the Parylene anchors.
Adhesion Promotion: Silane A174 adhesion promoter was applied to enhance bonding between BDD and Parylene.
Parylene Coating: A 7 µm conformal Parylene-C layer was deposited, covering the front and wrapping around the BDD patterns.
Wafer Release (Transfer): The Si substrate was released using Deep Reactive-Ion Etching (DRIE), followed by isotropic etching of the remaining SiO₂ in BOE.

6CCVD Solutions & Capabilities

This research highlights the critical role of high-quality, customizable Boron-Doped Diamond films in next-generation flexible bioelectronics. 6CCVD is uniquely positioned to supply the necessary materials and engineering services to replicate, scale, and advance this work.

Applicable Materials for Replication and Extension

The flexible sensor requires heavily doped, thin-film diamond with excellent surface quality and uniformity. 6CCVD recommends the following materials:

6CCVD Material	Specification	Application Relevance
Heavy Boron-Doped PCD (BDD)	Resistivity: < 0.005 Ω·cm. Thickness: 0.1 µm to 500 µm.	Direct replacement for the active electrode material. Ensures wide potential window and low background current.
Microcrystalline PCD	Grain Size: Optimized for high electrochemical surface area and adhesion to polymer layers.	Matches the microcrystalline structure used in the paper, ideal for robust anchor formation and transfer processes.
Ultra-Thin BDD Wafers	Thickness control down to 0.1 µm.	Allows for optimization of sensor flexibility and minimizes material usage while maintaining electrochemical performance.

Customization Potential & Engineering Support

6CCVD’s in-house capabilities directly address the complex fabrication steps required for flexible diamond devices, offering significant advantages over standard material suppliers:

Custom Dimensions and Substrates:
- The paper utilized a 3-inch Si wafer for processing. 6CCVD can supply PCD wafers up to 125mm in diameter, enabling high-volume, large-scale fabrication necessary for commercializing flexible sensors.
- We offer custom laser cutting and shaping to produce the exact 4mm x 4.7mm electrode geometry required, or to create complex arrays for multi-site neural monitoring.
Precision Thickness Control:
- The research used a 2.7 µm BDD film. 6CCVD guarantees precise thickness control for both SCD and PCD films across the entire 0.1 µm to 500 µm range, essential for optimizing mechanical flexibility and electrochemical kinetics.
Integrated Metalization Services:
- While the paper focused on the BDD film, future integration requires robust electrical contacts. 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) tailored to specific adhesion and biocompatibility requirements, eliminating the need for external processing steps.
Surface Quality for Bio-Interfacing:
- The paper noted BDD’s excellent biocompatibility. For optimal performance and reduced biofouling, 6CCVD provides advanced polishing services achieving Ra < 5 nm for inch-size PCD, ensuring smooth surfaces critical for long-term implanted neural chemical sensing projects.
Global Supply Chain:
- 6CCVD provides reliable global shipping (DDU/DDP), ensuring researchers worldwide receive high-quality MPCVD diamond materials quickly and efficiently.

6CCVD’s in-house PhD team can assist with material selection, doping level optimization, and surface preparation protocols for similar flexible bioelectronic sensor projects, ensuring optimal performance for both outer-sphere (Ru(NH₃)₆²⁺/³⁺) and sluggish electron transfer systems (Dopamine).

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

View Original Abstract

This paper reports a flexible, diamond-polymer chemical sensor with three microelectrodes, which features a wide aqueous potential window and low background current from diamond and mechanical flexibility from the polymer.An improved wafer transfer process is developed to transfer boron-doped polycrystalline diamond (BDD) onto a thin Parylene-C substrate with good uniformity, strong adhesion, and high yield.The as-fabricated sensor shows a much wider potential window compared to an Au electrode, and a sensitivity of ~0.018mA/mm 2 ·mM through cyclic voltammetry for Ru(NH 3 ) 6 2+/3+ and 0.0012µA/mm 2 ·µM through chronoamperometry for dopamine (DA).

Tech Support

Original Source

DOI: https://doi.org/10.31438/trf.hh2016.87