Carbon Fiber Paper Sensor for Determination of Trimethoprim Antibiotic in Fish Samples

At a Glance

Metadata	Details
Publication Date	2023-03-29
Journal	Sensors
Authors	Álvaro Torrinha, Miguel Tavares, Vitória Dibo, Cristina Delerue‐Matos, Simone Morais
Institutions	Polytechnic Institute of Porto, Rede de Química e Tecnologia
Citations	9
Analysis	Full AI Review Included

Executive Summary

This analysis focuses on the development and validation of a highly sensitive, low-cost electrochemical sensor utilizing unmodified carbon fiber paper (CPS) for the determination of the antibiotic Trimethoprim (TMP) in complex food matrices.

Core Innovation: An unmodified, untreated Carbon Paper Sensor (CPS) was successfully employed as a working electrode, offering a simple, efficient, and environmentally friendly alternative to traditional or nanostructured electrodes (GCE, BDD).
High Analytical Performance: The optimized Square Wave Voltammetry (SWV) method achieved a competitive Limit of Detection (LOD) of 0.065 µM, with a linear range spanning 0.05 to 2 µM.
Sensitivity: The sensor demonstrated high sensitivity, calculated at 48.8 µA µM^-1 cm^-2, attributed to the high specific surface area and porosity of the carbon fiber material.
Mechanism: The oxidation of Trimethoprim on the CPS surface was determined to be a mixed electron transfer process controlled by both diffusion and adsorption, involving a two-electron and approximately one-proton transfer (z=2, m≈1).
Matrix Validation: The CPS was successfully validated for the first time in complex solid food samples (fish, Merluccius capensis), utilizing a QuEChERS solid-phase extraction cleanup procedure.
Accuracy: Recovery assays in spiked fish samples yielded excellent results (105.9 ± 1.8%), confirming the sensor’s robustness in challenging matrices.
Sustainability Advantage: The simplicity of the unmodified CPS minimizes processing costs and environmental footprint compared to sensors requiring complex nanostructuration or expensive materials.

Technical Specifications

Parameter	Value	Unit	Context
Working Electrode Material	Carbon Fiber Paper (Toray TGP-H-60)	N/A	Unmodified, untreated
Geometric Area (Immersed)	0.63	cm²	Used for current density calculation
Detection Technique	Square Wave Voltammetry (SWV)	N/A	Optimized method
Electrolyte	Britton-Robinson Buffer (BRB)	0.1 M	Optimized pH 7
SWV Amplitude (Optimum)	0.02	V	Maximizes peak height
SWV Frequency (Optimum)	50	Hz	Compromise between signal and noise
SWV Step Potential (Optimum)	0.015	V	Corresponds to 750 mV s^-1 scan rate
Deposition Potential (Optimum)	+0.7	V	Maximizes analyte accumulation
Deposition Time (Optimum)	60	s	Maximizes analyte accumulation
Linear Range (TMP)	0.05 to 2	µM	Concentration range for calibration
Limit of Detection (LOD)	0.065	µM	Analytical figure of merit (3.3σ/slope)
Sensitivity (Geometric)	48.8 ± 3.2	µA µM^-1 cm^-2	Mean sensitivity (n=3 curves)
Repeatability (RSD)	6	%	Seven measurements of 0.5 µM TMP
Reproducibility (RSD)	9	%	Five different CPS sensors (0.5 µM TMP)
Recovery in Fish Samples	105.9 ± 1.8	%	Standard addition method

Key Methodologies

Sensor Fabrication: Carbon Fiber Paper (Toray TGP-H-60) was cut to 2.5 x 0.7 cm². Electrical contact was established by covering one end with aluminum foil and connecting via a crocodile clip. No chemical or electrochemical pre-treatment was performed.
Electrochemical Setup: Experiments utilized a Metrohm Autolab PGSTAT12 potentiostat in a three-electrode configuration: CPS (working electrode), Ag/AgCl (3 M KCl) (reference electrode), and Platinum (counter electrode).
Electrolyte Optimization: Britton-Robinson Buffer (0.1 M) was tested across a pH range of 3 to 12. Optimum performance was achieved at pH 7, close to the pKa (6.6) of Trimethoprim.
SWV Parameter Optimization: Optimal SWV parameters were determined sequentially: Amplitude (0.02 V), Frequency (50 Hz), and Step Potential (0.015 V), balancing signal magnitude and reproducibility.
Electrodeposition Optimization: Analyte deposition was optimized at +0.7 V for 60 s, maximizing the accumulation of TMP prior to the SWV measurement.
Fish Sample Preparation (QuEChERS): Approximately 1 g of fish meat was spiked, mixed with 5 mL water and 5 mL acetonitrile, followed by the addition of QuEChERS salts (4 g MgSO₄, 1 g NaCl). The mixture was vortexed and centrifuged (4000 rpm).
Dispersive SPE Cleanup: The supernatant was subjected to dispersive Solid Phase Extraction (SPE) using a kit containing 150 mg C18 and 900 mg MgSO₄ to remove fats and proteins, followed by high-speed centrifugation (13,000 rpm).
Final Analysis: The cleaned extract was evaporated under a nitrogen stream, redissolved in 30:70 acetonitrile:buffer (v/v), and analyzed using the optimized SWV method via standard addition.

Commercial Applications

The use of simple, unmodified carbon fiber paper as a high-performance electrochemical transducer opens several avenues for commercial deployment, particularly where cost, portability, and disposability are critical factors.

Aquaculture and Food Safety: Development of rapid, portable screening devices for monitoring antibiotic residues (e.g., Trimethoprim, Sulfamethoxazole) in farmed fish, shellfish, and meat products, ensuring compliance with maximum residue limits (MRLs).
Environmental Water Quality Testing: Creation of low-cost, disposable sensors for in situ monitoring of Contaminants of Emerging Concern (CECs), specifically pharmaceuticals, in rivers, lakes, and wastewater effluent, supporting regulatory compliance and environmental risk assessment.
Point-of-Care (POC) Diagnostics (Veterinary/Human): Potential integration into paper-based analytical devices (PADs) for rapid, decentralized testing of drug metabolites or active compounds in biological fluids (e.g., urine, serum) where high sensitivity is required without complex lab infrastructure.
Electrochemical Sensor Manufacturing: The CPS methodology provides a blueprint for manufacturing highly sensitive, disposable electrodes without the need for expensive materials (like BDD) or complex nanostructuration techniques (like GCE modification), lowering production costs significantly.
Process Control in WWTPs: Deployment of robust sensors within wastewater treatment facilities to continuously track the degradation and removal efficiency of persistent pharmaceutical compounds.

View Original Abstract

The increase in anthropogenic pollution raises serious concerns regarding contamination of water bodies and aquatic species with potential implications on human health. Pharmaceutical compounds are a type of contaminants of emerging concern that are increasingly consumed and, thus, being frequently found in the aquatic environment. In this sense, an electrochemical sensor based on an unmodified and untreated carbon fiber paper (CPS—carbon paper sensor) was simply employed for the analysis of trimethoprim antibiotic in fish samples. First, the analytical conditions were thoroughly optimized in order for the CPS to achieve maximum performance in trimethoprim determination. Therefore, an electrolyte (0.1 M Britton-Robinson buffer) pH of 7 was selected and for square wave voltammetry parameters, optimum values of amplitude, frequency and step potential corresponded to 0.02 V, 50 Hz, and 0.015 V, respectively, whereas the deposition of analyte occurred at +0.7 V for 60 s. In these optimum conditions, the obtained liner range (0.05 to 2 µM), sensitivity (48.8 µA µM−1 cm−2), and LOD (0.065 µM) competes favorably with the commonly used GCE-based sensors or BDD electrodes that employ nanostructuration or are more expensive. The CPS was then applied for trimethoprim determination in fish samples after employing a solid phase extraction procedure based on QuEChERS salts, resulting in recoveries of 105.9 ± 1.8% by the standard addition method.

Tech Support

Original Source

DOI: https://doi.org/10.3390/s23073560

References

2017 - Pharmaceuticals and personal care products (PPCPs) in the freshwater aquatic environment [Crossref]
2018 - A review of the pharmaceutical exposome in aquatic fauna [Crossref]
2017 - Occurrences and removal of pharmaceuticals and personal care products (PPCPs) in drinking water and water/sewage treatment plants: A review [Crossref]
2012 - Emerging organic contaminants in groundwater in Spain: A review of sources, recent occurrence and fate in a European context [Crossref]
2019 - Pharmaceuticals in freshwater aquatic environments: A comparison of the African and European challenge [Crossref]
2022 - Pharmaceuticals in water as emerging pollutants for river health: A critical review under Indian conditions [Crossref]
2022 - Environmental contamination in a high-income country (France) by antibiotics, antibiotic-resistant bacteria, and antibiotic resistance genes: Status and possible causes [Crossref]