XMEA - A New Hybrid Diamond Multielectrode Array for the In Situ Assessment of the Radiation Dose Enhancement by Nanoparticles

At a Glance

Metadata	Details
Publication Date	2024-04-10
Journal	Sensors
Authors	Patrícia Nicolucci, Guilherme Gambaro, Kyssylla Monnyelle Araujo Silva, Iara Souza Lima, Oswaldo Baffa
Institutions	Universität Ulm, Universidade de São Paulo
Analysis	Full AI Review Included

XMEA: A New Hybrid Diamond Multielectrode Array for Radiation Dose Enhancement Assessment

This technical documentation analyzes the requirements and achievements of the XMEA device, a novel hybrid diamond sensor for radiobiology and dosimetry, and maps them directly to the advanced material and fabrication capabilities offered by 6CCVD (6ccvd.com).

Executive Summary

The research successfully developed and validated the XMEA, a highly versatile hybrid diamond device combining a Multielectrode Array (MEA) for biosensing with integrated Single-Crystal Diamond (SCD) photodiodes for X-ray dosimetry.

Hybrid Architecture: The XMEA integrates a 16-channel Nanocrystalline Diamond (NCD) MEA layer (for electrophysiology/exocytosis studies) with a 4-quadrant intrinsic SCD (i-NCD) X-ray detector (p-i-m structure).
Dosimetry Performance: The SCD X-ray detectors exhibited excellent linearity in response to radiation dose, achieving a correlation coefficient of r² ≥ 0.9999 across 50 kVp, 80 kVp, and 100 kVp X-ray beams.
Dose Enhancement: The device quantitatively assessed the Dose Enhancement Factor (DEF) produced by metallic nanoparticles (AuNP, PtNP, AgNP) in aqueous media.
Key Material Results: Gold Nanoparticles (AuNP) produced the highest DEF, reaching a maximum of 3.1 (at 100 µg/mL), confirming the superior radiosensitization potential of high-Z materials in low-energy X-ray fields.
Fabrication Complexity: The device required advanced MPCVD growth of both NCD and heteroepitaxial SCD, precise Boron-Doping (BDD), and a complex layer transfer technique to achieve transparency and low-noise operation.
Application Potential: The XMEA proves to be a powerful tool for in situ assessment of nanoparticle-mediated radiosensitization, paving the way for advanced radiobiology and clinical studies.

Technical Specifications

Parameter	Value	Unit	Context
Maximum DEF (AuNP)	3.068 ± 0.316	N/A	At 100 µg/mL concentration (100 kVp X-rays)
Maximum DEF (PtNP)	1.907 ± 0.741	N/A	At 5 µg/mL concentration (100 kVp X-rays)
Maximum Shielding (AgNP)	0.631 ± 0.297	N/A	DEF < 1, indicating 37% dose reduction at 1000 µg/mL
X-ray Detector Linearity (r²)	≥ 0.9999	N/A	Response to air-kerma across all tested radiation qualities
BDD Layer Thickness (PD)	300	µm	Top p-type layer of the p-i-m photodiode structure
Aluminum Contact Thickness	200	nm	Common back contact (Schottky contact)
MEA Electrode Diameter	20	µm	Size of the µ-electrodes in the sensing area
SCD Bandgap Energy	5.45	eV	Minimum energy required for electron-hole pair generation
X-ray Tube Potential	100	kVp	Used for primary DEF measurements
SCD Detector Bias (Optional)	8	V	Used to approximately double the signal amplitude

Key Methodologies

The XMEA device fabrication and testing relied on specialized diamond growth and microfabrication techniques:

SCD Growth: Heteroepitaxial Single-Crystal Diamond (SCD) was grown using Chemical Vapor Deposition (CVD) to form the base intrinsic layer (i-NCD) of the X-ray detector.
BDD Layer Deposition: A thick (300 µm) Boron-Doped Diamond (BDD) layer was deposited to form the p-type contact of the p-i-m photodiode structure.
NCD MEA Fabrication: A 16-channel Nanocrystalline Diamond (NCD) Multielectrode Array was fabricated on a sacrificial silicon wafer.
Layer Transfer Technique: The NCD-MEA stack was transferred from the silicon carrier to a final glass carrier using a multi-step process involving acetone-solvable glue and Hydrofluoric Acid (HF) etching of the SiO₂ interlayer, ensuring transparency for inverted microscopy.
Metalization: A 200 nm thick Aluminum layer was applied as the common back contact, forming a Schottky contact for the p-i-m photodiode.
Irradiation Protocol: Dose enhancement measurements were conducted using a 100 kVp X-ray beam, chosen for its higher fluence at energies closer to the absorption edges of the high-Z nanoparticles (Au, Pt).
DEF Calculation: The Dose Enhancement Factor (DEF) was determined by comparing the integrated current signal from the diamond electrodes when exposed to nanoparticle solutions versus pure water.

6CCVD Solutions & Capabilities

The XMEA research highlights the critical need for high-quality, customized MPCVD diamond materials and advanced fabrication services. 6CCVD is uniquely positioned to supply the necessary components and engineering support to replicate, scale, and advance this research.

Applicable Materials

To replicate the XMEA device, researchers require precise control over doping and crystal structure. 6CCVD offers the following optimized materials:

Optical Grade Single Crystal Diamond (SCD): Required for the intrinsic (i) layer of the p-i-m photodiode. Our SCD offers the high purity necessary to maximize carrier mobility and lifetime, ensuring the high sensitivity and linearity (r² ≥ 0.9999) demonstrated in the paper.
Heavy Boron Doped Diamond (BDD): Essential for the 300 µm thick p-type layer of the photodiode and the NCD MEA electrodes. 6CCVD provides BDD layers in both SCD and PCD formats, with precise doping control for optimal electrical conductivity and contact formation.
Polycrystalline Diamond (PCD) Wafers: NCD is a form of PCD. We supply high-quality PCD plates up to 125mm in diameter, enabling the scale-up of MEA fabrication for high-throughput radiobiology studies.

Customization Potential

The XMEA device relies heavily on custom dimensions, specific layer thicknesses, and tailored metal contacts—all core capabilities of 6CCVD.

XMEA Requirement	6CCVD Customization Service	Benefit to Researcher
Thick BDD Layer (300 µm)	Custom Thickness Control (0.1 µm to 500 µm)	We guarantee precise thickness for both SCD and PCD layers, crucial for optimizing the internal electric field and charge collection efficiency in p-i-m structures.
Custom Metalization (200 nm Al)	In-House Metalization Services	We offer deposition of single or multi-layer stacks (Au, Pt, Pd, Ti, W, Cu, Al) with precise thickness control, ensuring reliable ohmic or Schottky contacts for both the MEA and the photodiode.
Microelectrode Patterning (20 µm)	High-Resolution Laser Cutting & Etching	6CCVD can pattern complex electrode geometries and define the active sensing areas with high precision, supporting the development of next-generation MEA designs.
Ultra-Smooth Surface Finish	Polishing Services (Ra < 1nm SCD, < 5nm PCD)	Critical for MEA applications, our polishing ensures optimal cell adhesion and minimizes noise, enhancing the sensitivity required for detecting low-level exocytotic events.

Engineering Support

The successful development of the XMEA requires expertise in both diamond material science and radiation physics.

Application Expertise: 6CCVD’s in-house PhD team specializes in material selection and optimization for advanced applications, including Diamond Dosimetry, Radiobiology, and Electrochemical Biosensing.
Material Consultation: We can assist researchers in optimizing the SCD/BDD layer structure (e.g., thickness and doping concentration) to maximize the Response Enhancement Factor (REF) and Dose Enhancement Factor (DEF) for specific X-ray energies (e.g., 100 kVp beams).
Global Logistics: We provide reliable global shipping (DDU default, DDP available) to ensure prompt delivery of custom diamond wafers and finished devices worldwide.

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

View Original Abstract

This work presents a novel multielectrode array (MEA) to quantitatively assess the dose enhancement factor (DEF) produced in a medium by embedded nanoparticles. The MEA has 16 nanocrystalline diamond electrodes (in a cell-culture well), and a single-crystal diamond divided into four quadrants for X-ray dosimetry. DEF was assessed in water solutions with up to a 1000 µg/mL concentration of silver, platinum, and gold nanoparticles. The X-ray detectors showed a linear response to radiation dose (r2 ≥ 0.9999). Overall, platinum and gold nanoparticles produced a dose enhancement in the medium (maximum of 1.9 and 3.1, respectively), while silver nanoparticles produced a shielding effect (maximum of 37%), lowering the dose in the medium. This work shows that the novel MEA can be a useful tool in the quantitative assessment of radiation dose enhancement due to nanoparticles. Together with its suitability for cells’ exocytosis studies, it proves to be a highly versatile device for several applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s24082409

References

2020 - Gold nanoparticles as radiosensitizers in cancer radiotherapy [Crossref]
2010 - Gold nanoparticles as radiation sensitizers in cancer therapy [Crossref]
2009 - The dosimetric feasibility of gold nanoparticle-aided radiation therapy (gnrt) via brachytherapy using low-energy gamma-/x-ray sources [Crossref]
2017 - Biological mechanisms of gold nanoparticle radiosensitization [Crossref]
2022 - Gold nanoparticles enhancing generation of ros for Cs-137 radiotherapy [Crossref]
2015 - Targeted gold nanoparticles enhance sensitization of prostate tumors to megavoltage radiation therapy in vivo [Crossref]
2022 - Radiation dose enhancement in megavoltage radiation therapy using au, gd, pt, ag, and bi nanoparticles of various concentration level