New strategies for obtaining the SERS effect in organic solvents

Significance of the topic

The integration of electrochemistry and surface-enhanced Raman scattering (SERS) creates a powerful strategy for producing active substrates in a single experiment and dramatically boosting Raman signals. Extending EC-SERS protocols to organic solvents opens avenues for analyzing compounds that are insoluble or unstable in water, such as certain dyes and pesticides, thereby expanding the technique’s applicability in environmental, industrial, and pharmaceutical contexts.

Objectives and Study Overview

This study aims to establish and demonstrate electrochemical activation procedures for gold and silver electrodes in nonaqueous media to generate SERS-active surfaces. The work focuses on detecting crystal violet in acetonitrile and mancozeb in dimethyl sulfoxide (DMSO), assessing enhancement factors and analytical sensitivity.

Methodology and Instrumentation

• Instrument: SPELEC RAMAN combining a 785 nm laser, bipotentiostat/galvanostat, and spectrometer (785–1010 nm, 0–2850 cm-1).
• Probe and cell: Raman probe matched to 785 nm and a spectroelectrochemical cell for conventional electrodes.
• Electrodes: gold and silver working electrodes; steel counter electrode; Ag/AgCl reference electrode.
• Solvents and electrolyte: acetonitrile with 0.1 mol/L tetrabutylammonium hexafluorophosphate (TBA) for crystal violet; DMSO with 0.1 mol/L TBA for mancozeb.
• Electrochemical protocols: potential scans from +0.70 V to +2.00 V and back to –0.60 V for gold; +0.60 V to –0.60 V cycles for silver.

Key Results and Discussion

• Gold electrode activation produced nanostructures by oxidizing at +1.80 V and reducing at +1.03 V, leading to a significant increase in Raman intensity during the cathodic scan, with maximum signal at +0.20 V. The method achieved a detection limit of 1 µmol/L crystal violet based on the 1175 cm-1 Raman band.
• Silver electrode activation required one pretreatment cycle followed by an activation cycle in DMSO. Characteristic mancozeb bands (240–1615 cm-1) were clearly detected at –0.60 V, and signal intensity remained stable from the second cycle onward, indicating reproducible enhancement.

Benefits and Practical Applications

This integrated EC-SERS approach simplifies substrate generation and allows sensitive detection of analytes in organic solvents without elaborate surface modifications. It is well suited for environmental screening of pesticides, quality control of synthetic dyes, and process monitoring in nonaqueous industrial operations.

Future Trends and Potential Applications

• Development of alternative electrode materials and nanostructuring strategies to further enhance sensitivity.
• Extension to a wider range of organic solvents and target analytes, including pharmaceuticals and biomarkers.
• Integration into microfluidic and portable platforms for on-site, real-time analysis.
• Application of advanced data processing and machine learning algorithms for automated spectral interpretation.

Conclusion

Electrochemical activation of gold and silver electrodes in organic media provides a versatile and sensitive EC-SERS platform. The successful detection of crystal violet and mancozeb underscores its potential for analyzing compounds insoluble in aqueous environments, paving the way for broader applications in analytical chemistry.

References

• González-Hernández J.; Ott C. E.; Arcos-Martínez M. J.; et al. Rapid Determination of the ‘Legal Highs’ 4-MMC and 4-MEC by Spectroelectrochemistry: Simultaneous Cyclic Voltammetry and In Situ Surface-Enhanced Raman Spectroscopy. Sensors 2022, 22(1), 295.
• Ibáñez D.; González-García M. B.; Hernández-Santos D.; Fanjul-Bolado P. Detection of Dithiocarbamate, Chloronicotinyl and Organophosphate Pesticides by Electrochemical Activation of SERS Features of Screen-Printed Electrodes. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2021, 248, 119174.