Low-coherence photonic method of electrochemical processes monitoring

At a Glance

Metadata	Details
Publication Date	2021-06-15
Journal	Scientific Reports
Authors	Monika Kosowska, Paweł Jakóbczyk, Michał Rycewicz, I. Alex Vitkin, Małgorzata Szczerska
Institutions	University of Toronto, Gdańsk University of Technology
Citations	6
Analysis	Full AI Review Included

Executive Summary

This research presents a novel, highly integrated hybrid platform for simultaneous opto-electrochemical (EC) monitoring of liquid samples, leveraging the unique properties of Boron-Doped Diamond (BDD).

Core Innovation: The system combines a fiber-optic Fabry-Perot Interferometer (FPI) with a standard three-electrode EC setup, sharing a single BDD film element.
BDD Dual Role: The BDD film acts simultaneously as the working electrode for the electrochemical reaction (Cyclic Voltammetry) and as the reflective mirror for the optical interferometry.
Non-Destructive Evaluation (NDE): Measurements of ferrocyanide redox reactions demonstrated stable optical spectra across multiple cycles, confirming the system operates in an NDE mode without irreversible sample alteration or hysteresis.
Optical Readout: The FPI monitors changes in the liquid’s refractive index or adsorption events on the BDD surface, providing complementary data to the EC current-voltage curves.
Engineering Advantages: The hybrid design significantly reduces required sample volume (potential for lab-on-chip), lowers construction cost by eliminating high-quality mirrors, and simplifies the setup due to the use of robust fiber optics.
Feasibility Confirmed: The system successfully registered expected EC redox peaks while simultaneously obtaining stable optical fringe visibility (median V = 0.48) during the reversible reaction cycles.

Technical Specifications

Parameter	Value	Unit	Context
Working Electrode Material	Boron-Doped Diamond (BDD)	Film	Deposited on silica substrate
BDD Active Area	0.2	cm²	Electrochemical cell area
Electrolyte Concentration	2.5	mM	K₃[Fe(CN)₆] in 0.5 M Na₂SO₄
EC Scan Rate	10	mV/s	Cyclic Voltammetry
Oxidation Peak Potential (A)	0.247	V	Anodic current peak
Reduction Peak Potential (B)	-0.027	V	Cathodic current peak
Optical Source Center Wavelength	1550	nm	Super Luminescence Diode (SLD)
Fringe Visibility (Median)	0.48	a.u.	Measured in liquid cavity (due to absorption loss)
Observed Spectral Shift	less than 0.5	nm	Attributed to light source instability
BDD Growth Temperature	700	°C	MPCVD graphite stage temperature
BDD Growth Pressure	50	Torr	MPCVD reactor pressure
BDD Microwave Power	1300	W	MPCVD system
BDD Dopant Ratio ([B]/[C])	10,000	ppm	Diborane precursor ratio
Nanodiamond Seeding Size	4-7	nm	Used for substrate preparation

Key Methodologies

The hybrid system relies on the precise fabrication of the BDD film and the integration of standard fiber-optic and electrochemical components.

BDD Film Deposition (MPCVD):
- A 2.45 GHz Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD) system was used on 1 cm x 1 cm p-type silicon (100) substrates.
- Substrates were seeded using a slurry of undoped nanodiamonds (4-7 nm).
- Growth parameters were maintained at 50 Torr pressure, 1300 W microwave power, and 700 °C graphite stage temperature.
- Methane, hydrogen, and diborane were used, maintaining a [B]/[C] ratio of 10,000 ppm for 12 hours.
Electrochemical Cell Setup:
- A standard three-electrode configuration was used: BDD film (working electrode, 0.2 cm² active area), silver/silver chloride (Ag/AgCl) wire (reference electrode), and Platinum (Pt) wire (counter electrode).
- Electrodes were connected to a potentiostat-galvanostat for potential control and current recording (Cyclic Voltammetry).
- The electrolyte used was 2.5 mM K₃[Fe(CN)₆] in 0.5 M Na₂SO₄ solution.
Fabry-Perot Interferometer (FPI) Integration:
- The FPI was constructed using a 1550 nm SLD light source and an Optical Spectrum Analyzer (OSA) for detection.
- A single-mode optical fiber, stripped and cleaved, served as the measurement head.
- The FPI cavity was formed between the fiber end-face/liquid interface (reference reflection) and the liquid/BDD film interface (measurement reflection).
- The optical fiber was positioned parallel and close to the BDD film surface within the electrochemical cell, ensuring the BDD acted as the reflective layer.
Simultaneous Measurement Protocol:
- Cyclic Voltammetry was performed at a 10 mV/s scan rate, monitoring the Fe(CN)₆^3-/Fe(CN)₆^4- redox peaks.
- Optical spectra were recorded simultaneously before and after each full EC cycle, repeated five times, to confirm reversibility and NDE operation.

Commercial Applications

This hybrid opto-electrochemical monitoring technology, particularly due to its reliance on BDD and fiber optics, is highly relevant for applications requiring high sensitivity, miniaturization, and real-time feedback.

Industry/Sector	Application Focus	Technical Advantage
Environmental Monitoring	Detection and degradation monitoring of heavy metals and organic pollutants in water.	BDD robustness and wide potential window; NDE monitoring of degradation processes.
Biomedical/Biosensing	Real-time detection of small concentrations of biomolecules (e.g., glucose, proteins, DNA, neurotransmitters).	High sensitivity and biocompatibility of BDD electrodes; miniaturization potential for in vivo or lab-on-chip devices.
Chemical Process Control	Continuous, real-time monitoring of reaction kinetics, especially in small volume or microfluidic systems.	Quick operation and low sample volume requirements; simultaneous optical and electrical feedback for process optimization.
Electrode Surface Analysis	In situ monitoring of adsorption/desorption events or polymer doping on electrode surfaces.	Optical readout (refractive index change) provides direct confirmation of surface modification during EC cycles.
Miniaturized Diagnostics	Development of robust, low-cost, disposable lab-on-chip devices for field testing.	Utilizes only one dual-role element (BDD) and simple fiber-optic components, enabling high integration density.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-021-91883-z