SERS detection of pesticides using screen-printed electrodes

Importance of the Topic

The reliable detection of trace pesticide residues is essential for environmental monitoring, food safety, and regulatory compliance. Conventional Raman spectroscopy often lacks the sensitivity needed for low-concentration analysis. Electrochemical surface-enhanced Raman scattering (EC-SERS) combines electrochemical activation with SERS to amplify Raman signals, offering a promising route to rapid, high-sensitivity pesticide screening without complex sample preparation.

Objectives and Study Overview

This application note describes the development of an EC-SERS method for the detection of the fungicide thiram and the insecticide imidacloprid. Key goals include leveraging gold screen-printed electrodes (SPEs) as in situ SERS substrates, incorporating a simple preconcentration step, and achieving detection limits below European Union maximum residue limits using minimal instrumentation.

Methodology and Instrumentation

A two-stage EC-SERS procedure was implemented. First, a 60 µL sample droplet was deposited on a gold SPE and heated at 34 °C to reduce volume to 25 µL, increasing HCl concentration from 0.1 mol/L to 0.24 mol/L. Second, cyclic voltammetry (scan from +0.70 V to +1.40 V and back to −0.20 V at 0.05 V/s) generated gold nanoparticles on the electrode surface to enhance Raman scattering. Raman spectra were recorded continuously using a 785 nm laser.

Used Instrumentation:

• SPELEC RAMAN instrument (785 nm laser)
• RAMANPROBE matched to laser wavelength
• RAMAN spectroelectrochemical cell for SPEs (RAMANCELL)
• Gold screen-printed electrodes (220BT)
• Connection cable for SPEs (CAST)
• DropView SPELEC software for synchronized spectroelectrochemical control and data analysis

Key Results and Discussion

Thiram analysis focused on the Raman band at 1380 cm⁻¹. Using the preconcentration and EC-SERS steps, clear signals were obtained down to 12 µg/L, and after baseline correction by polynomial fitting, down to 2.4 µg/L—well below the EU maximum residue limit of 0.1 mg/L.
Imidacloprid detection targeted the 1107 cm⁻¹ band, achieving a limit of 25 µg/L. EU regulations set imidacloprid limits between 0.05 and 10 mg/L, demonstrating that the method satisfies required sensitivity.
When applied to tap water spiked with thiram, the 3 µg/L and 20 µg/L samples were readily detected, while the 1 µg/L concentration fell below the practical detection threshold.

Benefits and Practical Applications

The EC-SERS approach offers:

• Rapid, label-free detection without lengthy sample pretreatment
• High sensitivity compatible with EU regulatory limits
• Portable instrumentation suitable for field and laboratory use
• Broad applicability to different pesticide chemistries

These features make it attractive for environmental surveillance, food quality control, and on-site testing scenarios.

Future Trends and Potential Applications

Advancements may include optimized nanostructure engineering to lower detection limits further, integration with microfluidic platforms for automated sample handling, and development of handheld EC-SERS devices for in-field analysis. Coupling EC-SERS data with machine learning algorithms could enable real-time quantitative monitoring of multiple analytes.

Conclusion

This study demonstrates that electrochemically activated gold SPEs combined with a simple preconcentration protocol and EC-SERS detection enables sensitive, efficient monitoring of thiram and imidacloprid at concentrations below regulatory thresholds. The method’s speed, ease of use, and minimal equipment requirements position it as a powerful tool for pesticide residue analysis.

References

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