Neuronal growth on high-aspect-ratio diamond nanopillar arrays for biosensing applications

At a Glance

Metadata	Details
Publication Date	2023-04-11
Journal	Scientific Reports
Authors	Elena Losero, Somanath Jagannath, Maurizio Pezzoli, Valentin Goblot, Hossein Babashah
Institutions	École Polytechnique Fédérale de Lausanne, The University of Sydney
Citations	29
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Aspect-Ratio Diamond Nanopillar Arrays for Biosensing

This document analyzes the research paper “Neuronal growth on high-aspect-ratio diamond nanopillar arrays for biosensing applications” to provide technical specifications and align the findings with 6CCVD’s advanced MPCVD diamond capabilities, focusing on quantum biosensing and neural interface applications.

Executive Summary

This research validates the use of high-aspect-ratio single crystal diamond (SCD) nanopillar arrays as a robust, biocompatible platform for next-generation nitrogen-vacancy (NV) center quantum biosensing.

Biocompatibility Confirmed: Successfully demonstrated the growth and functional viability of living primary mouse hippocampal neurons on nanostructured SCD surfaces.
Nanostructure Performance: High-aspect-ratio pillars (up to 2 µm height, > 10:1 aspect ratio) enhance photoluminescence (PL) collection efficiency by +15% via waveguiding, crucial for maximizing quantum signal readout.
Functional Neurons: Electrophysiology confirmed that neuronal activity (action potentials, EPSPs) on the nanopillar arrays is functional and comparable to flat reference substrates, with no obvious alteration in activity.
Morphological Guidance: Neurite growth is preferentially guided along the nanopillar grid axes for pitches p ≤ 4 µm, enabling tailored network design and precise spatial alignment for sub-cellular resolution recording.
Critical Material Gap: The study identifies the need to transition from optical-grade SCD (uniform 1.4 ppb NV concentration) to electronic-grade SCD with controlled, shallow NV layers (e.g., delta-doping) to achieve the high sensitivity required for mammalian neuron quantum monitoring.
Scalability Demonstrated: The nanofabrication protocol is reliable and scalable, producing uniform arrays covering 2 mm x 2 mm areas, limited only by the starting substrate size.

Technical Specifications

The following hard data points were extracted from the nanofabrication and characterization sections of the paper:

Parameter	Value	Unit	Context
Substrate Material	Single Crystal CVD Diamond (100)	N/A	Optical Grade (Element6)
Substrate Dimensions	3 x 3 x 0.25	mm	Starting material size
Nanopillar Diameter (d) Range	100 to 500	nm	Varied across 25 arrays
Nanopillar Height (h)	~1 (up to 2)	µm	Achieved via optimized etch
Nanopillar Pitch (p) Range	1 to 10	µm	Varied for morphological study
Aspect Ratio (h:d)	> 10:1	N/A	Achieved via highly directional O₂-plasma etch
Array Coverage Area	2 x 2	mm	Total area covered (routinely > 10⁸ pillars)
Pre-Polishing Roughness (rms)	< 2	nm	Achieved via non-contact polishing
Diamond Etch Rate (O₂-plasma)	100	nm/min	STS Multiplex ICP parameters
NV Center Concentration	1.4	ppb	Uniformly distributed (Optical Grade)
PL Intensity Enhancement	+15	%	Compared to flat surface (waveguiding effect)
Resting Membrane Potential	-63 to -49	mV	Functional primary hippocampal neurons
EPSP Time Decay Constant (τ)	~ 25	ms	Typical physiological range

Key Methodologies

The large-scale, high-aspect-ratio nanopillar arrays were fabricated using a highly controlled top-down process flow:

Substrate Preparation: Commercial (100) SCD (3x3x0.25 mm) was cleaned (acetone, piranha solution) and subjected to preliminary non-contact polishing to remove residual mechanical damage and achieve a root mean square (rms) roughness of < 2 nm.
Hard Mask Deposition: 200 nm Titanium (Ti) hard mask was sputtered onto the polished SCD surface.
Resist Patterning: ~150 nm Hydrogen silsesquioxane (HSQ) negative resist was spin-coated, followed by high-resolution electron beam lithography (EBL) to define the pillar patterns (d=100-500 nm, p=1-10 µm).
Mask Etch: A Cl₂-based Reactive Ion Etching (RIE) process was used to pattern the Ti hard mask.
Diamond Etch (High Aspect Ratio): A highly directional O₂-plasma etch was performed (STS Multiplex ICP: 400 W ICP power, 200 W bias power, 30 sccm O₂, 15 mTorr). This process achieved an etch rate of 100 nm/min and resulted in vertical sidewalls and aspect ratios exceeding 10:1.
Mask Stripping: Residual HSQ and Ti masks were removed using diluted hydrofluoric acid (HF, 1% concentration).
Biological Preparation: SCD chips were coated sequentially with Poly-L-Lysine and Laminin to facilitate the growth of primary hippocampal neurons, which were maintained for 10-14 days in vitro (DIV).

6CCVD Solutions & Capabilities

The research successfully demonstrates the potential of nanostructured diamond for quantum neurosensing but explicitly calls for higher-grade materials and controlled NV placement to achieve the necessary sensitivity. 6CCVD is uniquely positioned to supply the advanced materials and customization required to move this research from proof-of-concept to a functional device.

Research Requirement / Challenge	6CCVD Solution & Capability	Technical Advantage
Substrate Material: Need for high-purity, electronic-grade diamond with negligible background NV centers.	Electronic Grade Single Crystal Diamond (SCD): We supply ultra-low nitrogen content SCD (< 1 ppb) plates up to 500 µm thick and substrates up to 10 mm thick.	Provides the ideal low-noise platform for quantum applications, ensuring maximum coherence time (T₂) for engineered NV centers.
Controlled NV Layer: Requirement for shallow, high-coherence NV centers near the pillar apex (not uniform bulk NVs).	Boron-Doped Diamond (BDD) / Delta-Doping: 6CCVD offers custom CVD growth recipes to create thin, highly controlled nitrogen-doped layers (delta-doping) just below the surface.	Essential for maximizing electric field coupling between the NV center and the neuronal membrane, achieving the high sensitivity needed for mammalian neuron detection.
Scalability & Size: Arrays were limited to 2 mm x 2 mm; future applications require wide-field, large-scale integration.	Custom Dimensions: 6CCVD supplies SCD substrates up to 10 mm thick and large-area Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter.	Enables researchers to scale up the nanophotonic platform for high-throughput studies of complex neuronal networks.
Surface Quality: Requirement for ultra-smooth surface (rms < 2 nm) prior to nanostructuring.	Precision Polishing: Our standard SCD polishing achieves Ra < 1 nm, and inch-size PCD achieves Ra < 5 nm.	Guarantees optimal starting material quality, minimizing defects that interfere with EBL and high-aspect-ratio dry etching processes.
Post-Processing: Need for Ti/Au/Pd coating for SEM imaging and potential future electrode integration (microelectrode arrays).	Custom Metalization: Internal capability to deposit Au, Pt, Pd, Ti, W, and Cu layers with precise thickness control.	Supports the integration of hybrid devices, combining nanophotonic sensing with traditional electrophysiology (patch clamp/MEAs).
Engineering Support: Guidance needed on material selection and doping strategy for optimal quantum biosensing platforms.	In-House PhD Engineering Team: Consultation services available for optimizing material grade, doping strategy, and surface functionalization for specific neurosensing projects.	Accelerates R&D cycles by providing expert material science guidance tailored to complex biological interfaces.

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/s41598-023-32235-x