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6CCVD Research

Novel Amperometric Sensor Based on Glassy Graphene for Flow Injection Analysis

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-04-13
JournalSensors
AuthorsRamtin E. Shabgahi, Alexander Minkow, Michael Wild, Dietmar Kissinger, A. Pasquarelli
InstitutionsDiamond Materials (Germany), UniversitÀt Ulm
Citations4
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research introduces a novel, cost-effective method for fabricating high-performance glassy graphene (GG) microelectrodes using pyrolyzed photoresist films (PPFs) and a nickel (Ni) catalyst via Rapid Thermal Annealing (RTA).

  • Core Value Proposition: GG acts as a stable, high-conductivity, and low-cost alternative to Boron-Doped Diamond (BDD) for advanced electrochemical sensing, compatible with lithographic microfabrication.
  • Fabrication Success: GG films were successfully synthesized on both SiO2/Si and Polycrystalline Diamond (PCD) substrates using RTA (800 °C to 950 °C), confirming the material’s intermediate structure between glassy carbon (GC) and few-layer graphene.
  • Substrate Dependence: PCD proved superior, providing stronger graphene-substrate adhesion, lower interfacial resistance (R1), and enhanced long-term stability compared to GG films on SiO2/Si, which suffered from delamination.
  • Optimized Performance: The GG/PCD sensor (950 °C, 1 min) achieved excellent analytical performance for adrenaline detection using Flow Injection Analysis (FIA) with amperometric detection.
  • Sensing Metrics: The optimal sensor achieved a high sensitivity of 1.029 ”A cm-2/”M and a low limit of detection (LOD) of 1.05 ”M in the linear range of 3-300 ”M adrenaline.
  • Electrochemical Characteristics: GG/PCD exhibited a wide potential window (1.68 V) and improved Heterogeneous Electron Transfer (HET) kinetics (ΔEp = 78.50 mV for [Ru(NH3)6]3+/2+) compared to precursor GC films.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Optimal Sensitivity1.029”A cm-2/”MGG/PCD (950 °C, 1 min) at 0.8 V
Limit of Detection (LOD)1.05”MGG/PCD (950 °C, 1 min) at 0.8 V
Linear Range3-300”MAdrenaline detection via FIA
Raman ID/IG Ratio0.14 ± 0.03DimensionlessGG/SiO2/Si (950 °C) (Low defect density)
Raman ID/IG Ratio0.23 ± 0.01DimensionlessGG/PCD (950 °C) (Higher disorder due to grain boundaries)
Raman I2D/IG Ratio0.73 ± 0.069DimensionlessGG/PCD (950 °C) (Multilayer graphene formation)
Potential Window (GG/PCD)1.68VMeasured in PBS (pH 7.4)
Double-Layer Capacitance (GG/PCD)72.98”F cm-2Measured in PBS (pH 7.4)
HET Kinetics (ΔEp)78.50 ± 2mVGG/PCD (950 °C) using [Ru(NH3)6]3+/2+ marker
Film Thickness (Post-RTA)160 ± 10nmGC film derived from 1.3 ”m photoresist
RMS Roughness (GG/PCD)28.10nmGG/PCD (950 °C, 1 min)
Ni Catalyst Thickness50nmDeposited via thermal evaporation
RTA Peak Temperature950°CGraphitization step (1 min hold)

Key Methodologies

Section titled “Key Methodologies”

The fabrication of the GG microelectrodes involved a multi-step lithographic and thermal process on both SiO2/Si and PCD substrates:

  1. Substrate Preparation:
    • SiO2/Si wafers were cleaned and coated with a 1 ”m PECVD SiO2 insulating layer.
    • PCD substrates were cleaned using chromosulfuric acid (80 °C, 20 min) to remove non-diamond carbon (NDC).
  2. Photoresist Patterning (PPF Precursor):
    • Image reversal photoresist (AZ 5214E) was spin-coated (4000 rpm, 60 s).
    • UV photolithography and image reversal bake (110 °C, 90 s) defined the microelectrode geometry.
  3. Pyrolysis (GC Formation):
    • A two-step RTA process was performed under high-purity N2 atmosphere (3000 sccm).
    • Step 1 (Curing): Ramp to 350 °C over 10 min, hold for 60 min (stabilization).
    • Step 2 (Graphitization): Ramp to 450 °C (7.5 °C/s), hold for 5 min, then ramp to 950 °C (20 °C/s), hold for 1 min.
  4. Ni Catalyst Deposition:
    • A thin layer (50 nm) of nickel (Ni) was thermally evaporated onto the PPF (now GC) electrodes.
    • A lift-off process removed excess Ni, leaving the catalyst only on the electrode stripes.
  5. GG Conversion:
    • A second RTA process was performed using the same protocol as Step 2 (up to 950 °C, 1 min hold) to convert the Ni-coated GC into Glassy Graphene (GG) via metal-induced crystallization (MIC) and layer exchange.
  6. Electrochemical Testing:
    • Electrodes were tested using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) in Phosphate-Buffered Saline (PBS, pH 7.4).
    • Flow Injection Analysis (FIA) with chronoamperometric detection was used for quantitative adrenaline sensing (0.62 mL/min flow rate).

Commercial Applications

Section titled “Commercial Applications”

The development of stable, high-performance glassy graphene electrodes on diamond substrates is highly relevant for advanced electrochemical systems, particularly those requiring stability, low background noise, and high sensitivity.

Industry/ApplicationRelevance to GG/PCD Technology
Neurotransmitter DetectionHigh sensitivity (1.029 ”A cm-2/”M) and stability for detecting catecholamines (e.g., adrenaline, dopamine) in physiological media. Essential for neurological research and diagnostics.
Flow Injection Analysis (FIA)GG/PCD electrodes are robust and compatible with automated, continuous monitoring systems, minimizing surface fouling common in stationary cells.
Biomolecule SensingThe high specific surface area and enhanced HET kinetics of GG make it suitable for developing biosensors for proteins, nucleic acids, and other electroactive targets.
Cost-Effective MicroelectrodesUtilizing photoresist as a carbon precursor allows for scalable, lithography-compatible fabrication, offering a low-cost alternative to expensive BDD electrodes.
ElectrocatalysisThe presence of embedded Ni-rich particles within the GG matrix enhances the Oxygen Evolution Reaction (OER) kinetics, suggesting potential use in energy storage or conversion devices.
Diamond Materials MarketReinforces the utility of Polycrystalline Diamond (PCD) as a robust, chemically inert substrate for integrating next-generation carbon materials like GG, enhancing the market for advanced diamond electrodes.
View Original Abstract

Flow injection analysis (FIA) is widely used in drug screening, neurotransmitter detection, and water analysis. In this study, we investigated the electrochemical sensing performance of glassy graphene electrodes derived from pyrolyzed positive photoresist films (PPFs) via rapid thermal annealing (RTA) on SiO2/Si and polycrystalline diamond (PCD). Glassy graphene films fabricated at 800, 900, and 950 °C were characterized using Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) to assess their structural and morphological properties. Electrochemical characterization in phosphate-buffered saline (PBS, pH 7.4) revealed that annealing temperature and substrate type influence the potential window and double-layer capacitance. The voltammetric response of glassy graphene electrodes was further evaluated using the surface-insensitive [Ru(NH3)6]3+/2+ redox marker, the surface-sensitive [Fe(CN)6]3−/4− redox couple, and adrenaline, demonstrating that electron transfer efficiency is governed by annealing temperature and substrate-induced microstructural changes. FIA with amperometric detection showed a linear electrochemical response to adrenaline in the 3-300 ”M range, achieving a low detection limit of 1.05 ”M and a high sensitivity of 1.02 ”A cm−2/”M. These findings highlight the potential of glassy graphene as a cost-effective alternative for advanced electrochemical sensors, particularly in biomolecule detection and analytical applications.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2008 - Advanced carbon electrode materials for molecular electrochemistry [Crossref]
  2. 2022 - Boron-Doped Diamond Electrodes: Fundamentals for Electrochemical Applications [Crossref]
  3. 2015 - A practical guide to using boron doped diamond in electrochemical research [Crossref]
  4. 2001 - Electroanalytical performance of carbon films with near-atomic flatness [Crossref]
  5. 2009 - Simultaneous decoupled detection of dopamine and oxygen using pyrolyzed carbon microarrays and fast-scan cyclic voltammetry [Crossref]
  6. 2013 - Pyrolyzed photoresist electrodes for integration in microfluidic chips for transmitter detection from biological cells [Crossref]
  7. 2003 - Performance of pyrolyzed photoresist carbon films in a microchip capillary electrophoresis device with sinusoidal voltammetric detection [Crossref]
  8. 2001 - Surface studies of carbon films from pyrolyzed photoresist [Crossref]
  9. 2009 - Lithographically defined porous carbon electrodes [Crossref]
  10. 2021 - A historical review of glassy carbon: Synthesis, structure, properties and applications [Crossref]

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