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 Ribeirão Preto
Analysis	Full AI Review Included

Executive Summary

This research introduces the XMEA, a novel hybrid diamond Multielectrode Array designed for the quantitative in situ assessment of the Radiation Dose Enhancement Factor (DEF) produced by metallic nanoparticles (NPs).

Hybrid Architecture: The XMEA combines a 16-channel nanocrystalline diamond (NCD) MEA (for electrochemical sensing and DEF measurement in the medium) with a 4-quadrant single-crystal diamond (SCD) detector (for coupled X-ray dosimetry).
Quantitative DEF Assessment: The device successfully measured DEF for silver (AgNPs), platinum (PtNPs), and gold (AuNPs) in aqueous solutions irradiated with 100 kVp X-rays, across concentrations up to 1000 µg/mL.
Superior Enhancement (AuNPs): Gold nanoparticles yielded the highest DEF, reaching a maximum enhancement factor of 3.1 at 100 µg/mL, demonstrating significant dose increase in the surrounding medium.
Shielding Effect (AgNPs): Silver nanoparticles produced a dose shielding effect (DEF less than 1), resulting in a maximum dose reduction of 37% at the highest concentration tested (1000 µg/mL).
Dosimetry Performance: The integrated SCD X-ray detectors exhibited excellent linearity in response to air-kerma (r² greater than or equal to 0.9999) across all tested beam qualities (50, 80, and 100 kVp).
Versatility: The XMEA is proven to be a highly versatile tool, suitable for quantitative radiobiology studies of dose enhancement and simultaneous electrochemical detection (e.g., cellular exocytosis).

Technical Specifications

Parameter	Value	Unit	Context
Device Type	Hybrid Diamond MEA (XMEA)	-	Stacked NCD MEA (top) and SCD Detector (bottom)
NCD MEA Channels	16	-	Planar array for electrochemical detection
NCD µ-Electrode Size	20	µm	Sensing area dimension
SCD Detector Size	10 x 10 x 1	mm³	Heteroepitaxial single-crystal diamond
SCD Detector Structure	4-quadrant p-i-m	-	Boron-doped diamond (BDD) top layer
BDD Layer Thickness	300	µm	Top contact of the photodiode
Aluminum Contact Thickness	200	nm	Common back contact (Schottky)
X-ray Linearity (r²)	greater than or equal to 0.9999	-	Response to air-kerma (50, 80, 100 kVp)
Sensitivity (100 kVp)	13.5 ± 0.03 x 10^-4	pA/mGy	X-ray detector sensitivity
Sensitivity (50 kVp)	24.6 ± 0.14 x 10^-4	pA/mGy	Highest sensitivity observed (lower energy beam)
AuNP Max DEF	3.1	-	At 100 µg/mL (100 kVp X-rays)
PtNP Max DEF	1.9	-	At 5 µg/mL (100 kVp X-rays)
AgNP Max Shielding	37% (DEF 0.631)	-	At 1000 µg/mL (100 kVp X-rays)
Nanoparticle Concentration Range	5 to 1000	µg/mL	Tested range for Ag, Pt, and Au NPs
Nanoparticle Size (TEM, AuNPs)	4.4 ± 0.08	nm	Spherical morphology

Key Methodologies

NCD MEA Fabrication and Transfer: The nanocrystalline diamond (NCD) MEA was initially fabricated on a silicon wafer. The active diamond stack (intrinsic diamond, boron-doped diamond, and passivation) was subsequently transferred to a glass carrier using a multi-step gluing and etching process (HF acid for SiO₂ interlayer dissolution) to achieve transparency and low-noise characteristics.
SCD Detector Integration: A 10 x 10 x 1 mm³ heteroepitaxial single-crystal diamond (SCD) grown via Chemical Vapor Deposition (CVD) was structured into four p-i-m photodiode quadrants. This SCD detector forms the lower device of the XMEA stack, providing coupled X-ray monitoring capability.
Nanoparticle Synthesis: Silver (AgNPs), Platinum (PtNPs), and Gold (AuNPs) were synthesized using chemical reduction methods. Sodium borohydride (NaBH₄) was used as the strong reducing agent for all metal precursor salts (AgNO₃, H₂PtCl₆•6H₂O, HAuCl₄). Polyvinyl alcohol (PVA) was added to the PtNP mixture to prevent aggregation.
Nanoparticle Characterization: Particle formation was confirmed via UV-vis spectroscopy, identifying characteristic Surface Plasmon Resonance (SPR) absorption bands. Morphology and primary size distribution were analyzed using Transmission Electron Microscopy (TEM). Hydrodynamic size and stability were assessed using Dynamic Light Scattering (DLS).
Irradiation Setup: Low-energy X-ray beams were generated using a Konica Minolta X-ray tube (Altus ST 543 HF). Dose enhancement measurements utilized 100 kVp X-rays. Air-kerma was measured using a calibrated PTW ionization chamber (TN34069-2.5).
DEF Calculation: The Dose Enhancement Factor (DEF) was calculated as the ratio of the charge collected by the NCD MEA electrodes when the nanoparticle solution (1.5 mL, 2 mm height) was present, compared to the charge collected when only pure water was present.

Commercial Applications

The XMEA device and its underlying diamond technology are highly relevant to several high-value engineering and scientific fields:

Nanoparticle-Mediated Radiotherapy: Provides an essential tool for preclinical research, allowing quantitative in situ assessment of DEF for novel radiosensitizing nanoparticles (e.g., AuNPs, PtNPs) in media relevant to biological tissues.
Advanced Dosimetry: The integrated SCD detectors offer high-resolution, radiation-hard, and linear dose monitoring for low-energy X-rays, applicable in clinical radiation therapy quality assurance (QA) and research.
Electrochemical Biosensing: The NCD MEA component is optimized for high-sensitivity, real-time detection of cellular events, such as exocytosis (neurotransmitter release) and action potentials, crucial for neurobiology and drug screening.
Radiobiology Research: Enables synchronous measurement of radiation dose (SCD), dose enhancement (NCD), and cellular physiological response (NCD), facilitating true nanoparticle-mediated radiosensitization studies.
Diamond Material Science: Demonstrates a successful, complex transfer technique for NCD films onto glass, enhancing the transparency and noise performance of diamond-based sensors for optical and electrochemical applications.

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

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