Rapid Electrochemical Sensor for Polychlorinated Biphenyls Using β‑Cyclodextrin/Tin Disulfide‑Modified Screen‑Printed Carbon Electrodes

Abstract

Polychlorinated biphenyls (PCBs) are persistent, endocrine‑disrupting pollutants that pose serious health risks, including carcinogenesis and reproductive toxicity. This study presents the synthesis of a composite material comprising 3A‑amino‑3A‑deoxy‑(2AS,3AS)-β‑cyclodextrin hydrate (β‑CD) and tin disulfide (SnS₂) and its application as a modified screen‑printed carbon electrode (SPCE) for PCB detection. SnS₂ nanoflakes were produced hydrothermally, then sequentially deposited onto the SPCE by micropipette, followed by β‑CD coating. The resulting β‑CD/SnS₂/SPCE exhibits high conductivity and selective PCB binding through host–guest inclusion, enabling electrochemical monitoring via cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The sensor displays a linear detection range of 0.625–80 µM with a limit of detection (LOD) of 5 µM, and retains 88 % of its initial response after 7 days of storage.

Introduction

PCBs remain ubiquitous environmental contaminants due to their historical use in electrical insulation and their resistance to degradation. Despite regulatory bans, PCBs persist in soil, water, and biota, necessitating sensitive, rapid detection methods. Conventional analytical techniques—LC/MS and GC/MS—are accurate but costly, time‑consuming, and require skilled operators. Electrochemical sensing offers a low‑cost, portable alternative, yet few reports address PCB detection via modified electrodes. Enhancing electrode conductivity and selectivity through nanomaterials is essential; here, SnS₂ provides an n‑type semiconductor with high surface area, while β‑CD introduces a hydrophobic cavity that selectively encapsulates PCBs.

β‑Cyclodextrin (CD) is a cyclic oligosaccharide with a hydrophilic exterior and a hydrophobic interior cavity, enabling host–guest interactions with hydrophobic analytes. The 3A‑amino‑3A‑deoxy‑β‑CD variant offers improved solubility and functionalization potential. Tin disulfide (SnS₂) is a layered metal dichalcogenide (MDC) with a 2.2 eV indirect band gap, widely studied for electrochemical sensors due to its favorable electron‑transfer characteristics.

In this work, we synthesize SnS₂ nanoflakes via a hydrothermal route, combine them with β‑CD on an SPCE, and evaluate the composite’s electrochemical response to PCBs, demonstrating a rapid, selective, and stable sensor platform.

Materials and Methods

Materials

SnCl₄·5H₂O, thioacetamide, methanol, phosphate buffers, potassium ferrocyanide/ferricyanide, and 3A‑amino‑3A‑deoxy‑β‑CD were sourced from Alfa, Sigma‑Aldrich, and BaseChem. PCBs (Aroclor 1016) were purchased from Merck.

Instruments

Morphology was examined by FE‑SEM (ZEISS), phase analysis by XRD (PANalytical), and electrochemical measurements by CHI‑6114E in a conventional three‑electrode setup (SPCE as working, Ag/AgCl reference, Pt counter). Electrolytes were 3 mM ferro/ferricyanide + 0.1 M KCl or 10 mM PBS (pH 7.4). Potential window: −0.6 to +1.0 V; scan rate: 0.05 V s⁻¹.

Synthesis of Tin Disulfide

In 70 mL water, 0.351 g SnCl₄·5H₂O and 0.3 g thioacetamide were stirred for 1 h. 1 M NaOH was added dropwise to reach pH ≈ 10.5. The solution was transferred to a stainless‑steel autoclave, heated from 25 °C to 200 °C (1 h) and then held at 200 °C for 11 h. After cooling, the product was washed with water and ethanol, centrifuged (6000 rpm, 30 min), and dried.

Fabrication of β‑CD/SnS₂/SPCE

0.02 g SnS₂ was dispersed in 5 mL water; 2 µL of this suspension was pipetted onto the SPCE surface, dried in a vacuum dryer for 10 min, and repeated five times. Next, 2 µL of 1 mM β‑CD in water was applied, dried similarly, yielding the final composite electrode (see Fig. 2).

Rapid Electrochemical Sensor for Polychlorinated Biphenyls Using β‑Cyclodextrin/Tin Disulfide‑Modified Screen‑Printed Carbon Electrodes

Results and Discussion

Crystal Structure of SnS₂

XRD analysis confirmed the hexagonal SnS₂ phase (JCPDS 89‑2358), with characteristic peaks at 15°, 29°, 30°, 31°, 41°, 46°, 50°, 51°, 53°, and 70° (Fig. 3).

Morphology of SnS₂

FE‑SEM images revealed hexagonal nanoflakes with widths ranging from 220 nm to 322 nm (Fig. 4).

Electrochemical Impedance and Electrolyte Effect

Electrochemical impedance spectroscopy (EIS) showed that β‑CD/SnS₂/SPCE has the lowest charge‑transfer resistance, indicating superior conductivity (Fig. 5a). When tested in two electrolytes, the mixed ferro/ferricyanide + KCl solution produced a well‑defined redox peak, whereas PBS did not (Fig. 5b). Thus, the mixed electrolyte is optimal for PCB detection.

Electrochemical Response of Modified Electrodes

CV measurements in the mixed electrolyte demonstrated that SnS₂/SPCE outperforms bare SPCE, while β‑CD/SnS₂/SPCE shows the highest peak currents due to improved conductivity and lack of electron‑transfer barriers (Fig. 6a). Upon PCB addition, the peak current decreased sharply because β‑CD encapsulates PCBs, blocking the ferro/ferricyanide redox process.

Effect of Scan Rate

Peak currents increased linearly with √scan rate, yielding an electron‑transfer rate constant k_s = 0.039 s⁻¹ and surface coverage τ = 8.14 × 10⁻⁹ mol cm⁻².

Concentration Dependence

CV analysis showed negligible response changes below 2.5 µM PCBs; significant current reduction began at 5 µM. A linear relationship between log concentration (5–80 µM) and peak current (R² ≈ 0.98) confirms reliable quantification (Fig. 7).

Differential Pulse Voltammetry

DPV provided higher sensitivity, with a clear linear decline in peak current from 5 to 80 µM PCBs. The sensor’s LOD of 5 µM matches the CV results, and methanol addition lowered the LOD to 1.25 µM without compromising selectivity (Fig. 8–10).

Stability

After 7 days of storage at room temperature, the sensor retained 88 % of its initial current response, indicating robust operational stability (Fig. 11).

Conclusion

The hydrothermally synthesized SnS₂ nanoflakes, when combined with β‑CD on a screen‑printed carbon electrode, yield a sensitive and selective electrochemical sensor for PCBs. With a linear range of 0.62–80 µM, an LOD of 5 µM, and 88 % stability over 7 days, the β‑CD/SnS₂/SPCE platform offers a rapid, cost‑effective alternative to conventional chromatographic methods for on‑site PCB monitoring.