SERS detection of pesticides using screen-printed electrodes

Importance of the topic

The electrochemical surface-enhanced Raman scattering (EC-SERS) approach addresses the critical need for sensitive and rapid detection of trace pesticide residues in environmental and food matrices. Traditional Raman spectroscopy often lacks the sensitivity required for detecting low-concentration analytes such as thiram and imidacloprid. By harnessing electrochemically activated gold screen-printed electrodes (SPEs), this method enhances Raman signals and provides an accessible, cost-effective platform for field and laboratory applications.

Objectives and study overview

This study aims to develop and validate an EC-SERS protocol employing gold SPEs for the detection of thiram and imidacloprid at trace levels. It integrates a preconcentration step to improve sensitivity and relies on a single experimental setup that combines electrochemical nanoparticle formation with simultaneous Raman measurement. Avoiding extensive sample pretreatment and complex instrumentation, the method targets compliance with European Union maximum residue limits (MRLs) for these pesticides.

Methodology and instrumentation

• Preconcentration: A 60 µL droplet of pesticide solution is deposited on the SPE and heated at 34 °C for 15 minutes to reduce volume to 25 µL, concentrating HCl from 0.1 mol/L to 0.24 mol/L.
• Electrochemical activation: Potential scanned from +0.70 V to +1.40 V and back to –0.20 V (0.05 V/s) in the concentrated solution generates gold nanoparticles on the SPE surface.
• EC-SERS measurement: A 785 nm laser of the SPELEC RAMAN system collects Raman spectra during electrochemical cycling.

Instrumentation

• SPELEC RAMAN instrument (785 nm laser)
• RAMANPROBE spectroelectrochemical Raman probe
• RAMANCELL cell for screen-printed electrodes
• Gold SPE 220BT
• CAST connection cable
• DropView SPELEC software for synchronized spectroelectrochemical data acquisition and analysis

Main results and discussion

• Thiram detection: The Raman band at 1380 cm⁻¹ yielded detection limits as low as 2.4 µg/L after baseline correction, well below the EU MRL of 0.1 mg/L.
• Imidacloprid detection: The band at 1107 cm⁻¹ allowed detection down to 25 µg/L, meeting regulatory limits between 0.05 and 10 mg/L.
• Tap water analysis: Thiram spiked in tap water at 3 and 20 µg/L was clearly detected, while 1 µg/L fell below the method’s sensitivity threshold.

Benefits and practical applications

The EC-SERS technique offers rapid, sensitive, and straightforward pesticide detection without extensive sample preparation. Its portability and low-cost SPE substrates make it suitable for on-site environmental monitoring, food safety testing, and QA/QC laboratories, ensuring compliance with regulatory standards.

Future trends and opportunities

• Development of multiplex EC-SERS assays for simultaneous multi-pesticide screening.
• Integration with portable and smartphone-based Raman readers for field deployment.
• Advanced SPE substrate designs for enhanced reproducibility and signal stability.
• Automation and AI-driven spectral analysis to streamline data interpretation.
• Extension of EC-SERS to other contaminants such as pharmaceuticals and heavy metals.

Conclusion

The presented EC-SERS methodology successfully enhances Raman detection of thiram and imidacloprid using electrochemically activated gold SPEs and a simple preconcentration step. Achieving sub-MRL sensitivity and demonstrating applicability in tap water, this approach provides an efficient platform for trace pesticide analysis with broad potential in environmental and food safety contexts.

References

1. European Commission. EU Pesticides Database. https://food.ec.europa.eu/plants/pesticides/eu-pesticides-database_en (accessed 2025-06-26).