A Novel Thin-Layer Flow Cell Sensor System Based on BDD Electrode for Heavy Metal Ion Detection

At a Glance

Metadata	Details
Publication Date	2024-03-04
Journal	Micromachines
Authors	Danlin Xiao, Junfeng Zhai, Zhongkai Shen, Qiang Wang, Shengnan Wei
Institutions	State Key Laboratory of Transducer Technology, Changchun Institute of Applied Chemistry
Citations	6
Analysis	Full AI Review Included

Executive Summary

This research details the development of a highly efficient, automated electrochemical sensor system utilizing a Boron-Doped Diamond (BDD) working electrode integrated into a thin-layer flow cell for heavy metal ion detection via Anodic Stripping Voltammetry (ASV).

Core Innovation: Integration of a BDD electrode (offering a wide potential window) with a thin-layer flow cell (300 µm height, 20 µL volume) and an automated fluidic system.
Enhanced Efficiency: The flow-based system eliminates the need for conventional stirring, improving electrodeposition efficiency and enabling a short deposition time of only 60 s.
Trace Detection Capability: The system demonstrated a low limit of detection (LOD) for Zn²⁺ of 2.1 µg/L, with excellent linearity across 10 µg/L to 150 µg/L.
Low Consumption: Only 0.75 mL of reagent/sample is consumed per test, significantly reducing waste and secondary pollution risk, ideal for portable applications.
High Stability and Repeatability: The sensor exhibited high repeatability for Zn²⁺ detection, with a Relative Standard Deviation (RSD) of 1.60% over 30 consecutive tests.
Multi-Ion Capability: The wide potential window of the BDD electrode allowed for the simultaneous detection of Zn²⁺, Cd²⁺, and Pb²⁺, demonstrating potential for comprehensive on-site monitoring.

Technical Specifications

Parameter	Value	Unit	Context
Working Electrode Material	Boron-Doped Diamond (BDD)	N/A	Wide potential window (-2 V to +1 V)
Flow Cell Height	300	µm	Thin-layer design
Flow Cell Volume	20	µL	Electrochemical reaction cell volume
Sample/Reagent Consumption	0.75	mL	Per test
Deposition Time (Optimized)	60	s	For Zn²⁺ detection
Zn²⁺ Linear Range	10 to 150	µg/L	Individual detection
Zn²⁺ Sensitivity	0.1218	µA·L·µg^-1	Individual detection
Zn²⁺ Limit of Detection (LOD)	2.1	µg/L	Calculated (3σ/S)
Zn²⁺ Repeatability (RSD)	1.60	%	30 consecutive tests
Multi-Ion Linear Range	5 to 230	µg/L	Simultaneous detection (Zn²⁺, Cd²⁺, Pb²⁺)
Multi-Ion LOD (Pb²⁺)	0.17	µg/L	Simultaneous detection
Multi-Ion LOD (Cd²⁺)	0.53	µg/L	Simultaneous detection
Multi-Ion LOD (Zn²⁺)	0.80	µg/L	Simultaneous detection
Real Sample Recovery Range	92 to 118	%	Standard addition method

Key Methodologies

The sensor system relies on a customized thin-layer flow cell integrated with an automated fluidic control system and optimized ASV parameters for trace metal analysis.

Electrode Pretreatment (BDD):
- Initial cleaning: Soaking in acetone (10 min), followed by sonication in ethanol (5 min) and deionized water (5 min).
- Activation: Anode pretreatment (3 V constant potential, 360 s in 0.5 mol/L H₂SO₄), followed by cathode pretreatment (-3 V constant potential, 360 s in 0.5 mol/L H₂SO₄).
Flow Cell Design and Setup:
- The thin-layer flow cell secures the planar BDD working electrode between the main body and a back plate using silicone gaskets.
- A three-electrode system is used: BDD (Working), Platinum wire (Counter), and Ag/AgCl (Reference).
- The fluidic system uses a multi-channel syringe pump and a multiport selector valve to control sample flow and switching.
Electrolyte and Bi Film Deposition:
- Supporting Electrolyte: Acetic acid-sodium acetate buffer (0.1 mol/L, pH 4.5) containing 0.3 mol/L KCl to increase conductivity and reduce ohmic drop.
- Bismuth (Bi) Deposition: In situ deposition was used, with an optimized Bi concentration of 80 µg/L in the sample solution, forming a molten alloy with target ions to enhance stripping response.
Optimized ASV Detection Parameters (for Zn²⁺):
- Deposition Potential: -1.8 V (to maximize Zn reduction without excessive hydrogen evolution).
- Deposition Time: 60 s.
- Flow Rate (Deposition/Cleaning): 0.3 mL/min (continuous flow during deposition replaces conventional stirring).
- Stripping Method: Square Wave Voltammetry (SWV).
- SWV Pulse Amplitude: 100 mV.
Cleaning Step:
- Cleaning Potential: 1 V (applied after stripping to remove residual metals).
- Cleaning Time: 90 s.

Commercial Applications

The developed sensor system is highly relevant for applications requiring rapid, portable, and low-consumption analysis of heavy metal contaminants.

Environmental Monitoring and Water Quality:
- On-site, real-time monitoring of industrial wastewater discharge (e.g., monitoring Zn²⁺, Cd²⁺, and Pb²⁺ levels).
- Portable water quality testing for regulatory compliance and field surveys, especially where sample volume is limited.
Industrial Process Control:
- Monitoring metal ion concentrations in chemical baths or recycling streams where fast, automated feedback is critical.
BDD Electrode Technology Applications:
- The use of BDD electrodes, known for their wide potential window, low background current, and resistance to fouling, makes this technology suitable for harsh chemical environments.
- Potential use in other electrochemical sensing platforms requiring high stability and resistance to electrode contamination.

View Original Abstract

An electrochemical sensor based on a thin-layer flow cell and a boron-doped diamond (BDD) working electrode was fabricated for heavy metal ions determination using anodic stripping voltammetry. Furthermore, a fluidic automatic detection system was developed. With the wide potential window of the BDD electrode, Zn2+ with high negative stripping potential was detected by this system. Due to the thin-layer and fluidic structure of the sensor system, the electrodepositon efficiency for heavy metal ions were improved without using conventional stirring devices. With a short deposition time of 60 s, the system consumed only 0.75 mL reagent per test. A linear relationship for Zn2+ determination was displayed ranging from 10 μg/L to 150 μg/L with a sensitivity of 0.1218 μA·L·μg−1 and a detection limit of 2.1 μg/L. A high repeatability was indicated from the relative standard deviation of 1.60% for 30 repeated current responses of zinc solution. The system was applied to determine Zn2+ in real water samples by using the standard addition method with the recoveries ranging from 92% to 118%. The system was also used for the simultaneous detection of Zn2+, Cd2+, and Pb2+. The detection results indicate its potential application in on-site monitoring for mutiple heavy metal ions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi15030363

References

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2016 - Zinc finger peptide based optic sensor for detection of zinc ions [Crossref]
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2015 - Trace elements in seminal plasma of men from infertile couples
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2012 - Measurement of the Trace Elements Cu, Zn, Fe, and Mg and the Ultratrace Elements Cd, Co, Mn, and Pb in Limited Quantity Human Plasma and Serum Samples by Inductively Coupled Plasma-Mass Spectrometry [Crossref]