A wireless, implantable optoelectrochemical probe for optogenetic stimulation and dopamine detection

At a Glance

Metadata	Details
Publication Date	2020-08-23
Journal	Microsystems & Nanoengineering
Authors	Changbo Liu, Yu Zhao, Xue Cai, Yang Xie, Taoyi Wang
Institutions	Beihang University, Beijing Institute of Technology
Citations	99
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Advanced Neural Interfaces

Executive Summary

This documentation analyzes the successful integration of MPCVD diamond film into a wireless, implantable optoelectrochemical microprobe, highlighting the material’s critical role in achieving high-performance, minimally invasive neural interfaces.

Application Validation: Demonstrates a vertically stacked, miniaturized microprobe for simultaneous optogenetic stimulation (blue micro-LED) and real-time neurochemical sensing (dopamine detection) in the deep brain (VTA) of freely behaving mice.
Diamond Film Criticality: A 20 µm thick, polycrystalline diamond (PCD) layer is essential, serving simultaneously as an optically transparent (>80%) thermal heat spreader and a robust electrical insulator between the micro-LED and the PEDOT:PSS electrochemical sensor.
Superior Thermal Management: The ultrahigh thermal conductivity of the diamond (up to 2200 W/m/K) restricted the probe surface temperature increase to less than 2 °C at high pulsed currents (3 mA), mitigating the risk of tissue damage critical for in vivo applications.
High-Density Integration: The vertical stacking geometry, enabled by the thin-film diamond interlayer, achieves high spatial precision and a small footprint (needle shape, ~360 µm width), significantly reducing tissue lesions compared to traditional bundled fiber/wire approaches.
Electrochemical Performance: The integrated sensor achieved a dopamine detection limit as low as ~0.1 µM using differential pulse voltammetry (DPV), validating the diamond/PEDOT:PSS stack for sensitive neurochemical monitoring.
6CCVD Value Proposition: 6CCVD specializes in providing custom, high-purity MPCVD diamond materials (PCD and SCD) tailored for these complex, high-performance optoelectronic and electrochemical integration challenges.

Technical Specifications

The following hard data points were extracted from the research paper, validating the performance of the diamond-integrated microprobe:

Parameter	Value	Unit	Context
Diamond Material Type	Polycrystalline (PCD)	N/A	Undoped interlayer
Diamond Film Thickness	20	µm	Grown on Si via CVD
Diamond Lateral Dimensions	180 x 240	µm	Interlayer size
Diamond Thermal Conductivity	Up to 2200	W/m/K	Polycrystalline morphology
Diamond Optical Transmittance	> 80	%	Visible spectral range
Micro-LED Peak Wavelength	~470	nm	Optimal for ChR2 optogenetic stimulation
External Quantum Efficiency (EQE)	~10	%	LED coated with diamond/PEDOT:PSS (at ~1 mA)
Maximum Temperature Rise	< 2	°C	Probe surface, 3 mA pulsed current (20 Hz, 20% duty cycle)
Dopamine Detection Limit (DPV)	~0.1	µM	In HCl solutions (pH = 4.0)
Probe Needle Width	~360	µm	Minimally invasive geometry

Key Methodologies

The fabrication of the vertically stacked optoelectrochemical probe relied heavily on advanced thin-film processing and transfer techniques, utilizing MPCVD diamond as a core component.

Diamond Film Growth: Polycrystalline diamond (PCD) films (~20 µm thick) were grown on single-crystalline silicon substrates using Chemical Vapor Deposition (CVD).
Diamond Patterning and Release: The PCD film was patterned using Nd:YVO₄ laser milling (1064 nm) to achieve precise 180 µm x 240 µm dimensions. Freestanding films were realized by wet etching the underlying silicon substrate (CH₃COOH:HNO₃:HF = 5:5:2 volume ratio).
Micro-LED Fabrication and Release: InGaN-based blue micro-LEDs (7.1 µm total thickness) were grown via MOCVD on sapphire, patterned via ICP-RIE, and released using KrF excimer laser liftoff (248 nm, ~0.7 J/cm² power density).
Vertical Stacking via Transfer Printing: Freestanding LEDs and diamond films were sequentially transferred onto a flexible Cu/PI/Cu substrate using Polydimethylsiloxane (PDMS) stamping methods, utilizing SU-8 photoresist as the bonding/adhesive layer.
Electrode and Sensor Coating: Cr/Cu/Au and Cr/Au metal layers were sputtered for electrical contacts. The PEDOT:PSS thin film (~100 nm) was spin-cast onto the diamond surface to serve as the working electrochemical electrode and patterned via RIE (O₂/SF₆ plasma).
Final Shaping: The flexible substrate was patterned into a needle shape (width ~360 µm, length ~5 mm) using UV laser milling for implantation.

6CCVD Solutions & Capabilities

The successful fabrication of this advanced neural probe hinges on precise control over diamond material properties, dimensions, and integration interfaces—all core competencies of 6CCVD. We are uniquely positioned to supply the necessary materials and engineering support to replicate or extend this research.

Applicable Materials

The paper utilized a 20 µm thick, undoped Polycrystalline Diamond (PCD) film. 6CCVD offers materials optimized for both thermal and optical performance:

Optical Grade PCD Wafers: We supply high-purity PCD films (0.1 µm to 500 µm thickness) with guaranteed high optical transparency (>80%) and ultrahigh thermal conductivity (up to 2200 W/m/K), matching or exceeding the performance metrics required for this thermal spreading application.
Single Crystal Diamond (SCD) Option: For applications requiring even lower surface roughness (Ra < 1 nm) or superior thermal performance (up to 2000 W/m/K for SCD), 6CCVD offers optical-grade SCD plates up to 500 µm thick, ideal for minimizing light scattering and maximizing heat dissipation.
Heavy Boron-Doped Diamond (BDD) for Chronic Sensing: The authors noted the acute testing limitation due to electrode fouling. To address this, 6CCVD supplies highly conductive Heavy Boron-Doped Diamond (BDD) films. BDD electrodes offer exceptional electrochemical stability, wide potential windows, and resistance to fouling, making them the ideal material for chronic, in vivo neurotransmitter detection, extending the lifespan of the probe.

Customization Potential

6CCVD’s in-house manufacturing capabilities directly address the precise dimensional and integration requirements of microprobe fabrication:

Requirement in Paper	6CCVD Capability	Benefit to Researcher
Custom Dimensions (180 µm x 240 µm)	Precision UV Laser Milling and Cutting Services.	We provide custom-patterned PCD plates up to 125 mm in diameter, ensuring micro-scale geometries are met with high accuracy.
Thickness Control (20 µm)	SCD and PCD films available from 0.1 µm to 500 µm.	Researchers can easily scale the thermal budget by selecting precise thicknesses tailored to their specific LED power requirements.
Metalization (Cr/Cu/Au electrodes)	Internal metalization capability: Au, Pt, Pd, Ti, W, Cu.	We deliver diamond films pre-metalized with custom adhesion layers (e.g., Cr/Au or Ti/Pt/Au stacks) for reliable integration with flexible substrates and subsequent polymer coatings.
Polishing	SCD (Ra < 1 nm); Inch-size PCD (Ra < 5 nm).	Ultra-smooth surfaces minimize light scattering and ensure conformal coating of thin-film sensors like PEDOT:PSS.

Engineering Support

The successful integration of diamond as a multifunctional layer (thermal, optical, electrical isolation) requires deep material science expertise. 6CCVD’s in-house PhD team specializes in optimizing diamond properties (e.g., crystallinity, doping levels, surface termination) for advanced neural interfaces. We offer consultation services to assist engineers and scientists in selecting the optimal MPCVD diamond grade for similar optoelectrochemical, optogenetic, or thermal management projects.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41378-020-0176-9