New strategies for obtaining the SERS effect in organic solvents

Significance of the Topic

The combination of electrochemistry and surface-enhanced Raman scattering (SERS) in nonaqueous media addresses critical challenges in the detection of low-concentration analytes such as dyes and pesticides. Organic solvents often produce strong background signals, complicating conventional Raman analysis. The development of EC-SERS protocols in organic environments facilitates sensitive, in situ characterization of compounds that are insoluble or unstable in water, expanding analytical capabilities in chemical, environmental, and quality control applications.

Objectives and Study Overview

This study aims to demonstrate new strategies for generating SERS-active substrates via electrochemical activation of gold and silver electrodes in organic solvents. Key objectives include:

• Developing EC-SERS procedures compatible with acetonitrile and dimethyl sulfoxide (DMSO).
• Evaluating the detection of crystal violet dye and mancozeb pesticide at micromolar concentrations.
• Correlating electrochemical parameters with Raman enhancement factors.

Methodology and Experimental Procedure

Electrochemical activation involved scanning the electrode potential to form metallic nanostructures with SERS properties. For gold electrodes in acetonitrile with 0.1 mol/L tetrabutylammonium hexafluorophosphate (TBA): potentials were cycled from +0.70 V to +2.00 V and back to −0.60 V. Crystal violet at 0.1 mmol/L was monitored in situ. For silver electrodes in DMSO with 0.1 mol/L TBA: potentials ranged from +0.60 V to −0.60 V over five cycles to pretreat and activate the surface. Raman spectra were collected with a 785 nm laser and 2000 ms integration time during electrochemical scans.

Used Instrumentation

• SPELEC RAMAN spectroelectrochemical instrument (785 nm laser, 0–2850 cm⁻¹ Raman shift range).
• Bipotentiostat/Galvanostat integrated with Raman spectrometer.
• Raman probe matched to laser wavelength and spectroelectrochemical cell for conventional electrodes.
• Working electrodes: gold and silver tips; counter electrodes: steel; reference: Ag/AgCl.
• DropView SPELEC software for synchronized electrochemical and optical data acquisition.

Main Results and Discussion

• Gold electrodes in acetonitrile achieved a maximum Raman enhancement at +0.20 V during the cathodic scan. Crystal violet was detected down to 1 µmol/L, with well-defined vibrational bands (e.g., 1175 cm⁻¹).
• Silver electrodes in DMSO enabled detection of mancozeb pesticide. Characteristic bands at 240, 422, 463, 516, 560, 660, 912, 990, 1187, 1272, 1522, and 1615 cm⁻¹ were observed at −0.60 V after the second cycle, with signal stability through cycle 5.

Benefits and Practical Applications

• High analytical sensitivity and low detection limits for dyes and pesticides in organic media.
• Single-experiment correlation of electrochemical and spectroscopic data for real-time monitoring.
• Potential for rapid screening in environmental analysis, agrochemical monitoring, and quality control.

Future Trends and Potential Applications

Electrochemical SERS in organic solvents may evolve toward:

• Broader solvent compatibility and electrolyte optimization for diverse analytes.
• Miniaturized and portable EC-SERS platforms for field analysis.
• Integration with microfluidics and on-chip electrochemical reactors.
• Advanced electrode materials (bimetallic or nanoparticle-modified surfaces) for enhanced reproducibility.

Conclusion

Electrochemical activation of gold and silver electrodes in nonaqueous solvents offers a powerful route to generate SERS-active surfaces in a single experiment. The approach allows sensitive detection of crystal violet and mancozeb in acetonitrile and DMSO, respectively, achieving micromolar detection limits and stable signal enhancement. This methodology expands the analytical toolbox for challenging organic-soluble analytes and paves the way for versatile, in situ EC-SERS applications.

References

1. González-Hernández J, Ott CE, Arcos-Martínez MJ, 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.
2. Ibáñez D, González-García MB, 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 A Mol Biomol Spectrosc. 2021;248:119174.