Challenges in surface-enhanced Raman scattering signal for ethephon detection: Theoretical and experimental approaches

Author(s)

Bianchi-Carvalho, Isabela ; Martin, Cibely S. ; Alves, Gabriel G. B. ; Silva, Jaqueline N. ; Batagin-Neto, Augusto ; Constantino, Carlos J. L.

• Document type: Journal article
• Source: Journal of Raman Spectroscopy; v. 55, n. 1, p. 11-pg., 2023-11-12.

Abstract

Ethephon, a widely used growth regulator in fruits and vegetables, requires careful monitoring because of its toxicity. However, as far as we know, only two works are found in the literature regarding surface-enhanced Raman scattering (SERS) ethephon detection. Indeed, obtaining the SERS signal revealed to be challenging. Therefore, we have evaluated the SERS signal of ethephon using theoretical (as density functional theory and charge-assisted fragment interaction) and experimental approaches, addressing this limited literature knowledge. Theoretical Raman spectra with Ag or Au atoms at reactive sites exhibited enhanced ethephon SERS signal via Ag-Cl bonding, consistent with the experimental data. Multiple experimental procedures were employed to obtain the SERS signal, including pH variations, salt addition, excitation laser lines, time dependency, and different SERS substrates (Ag colloid and Ag island films). Salt addition (NaCl) improved SERS signal, correlating with Ag colloid aggregation. Analysis in Ag colloid showed the pH 7.0 as optimal for ethephon detection, using freshly prepared Ag colloid + ethephon dispersion with ethephon powder being directly dissolved into Ag colloid. Only the Ag-Cl band intensity improved with time. Ag colloid (wet medium - 633 nm laser line) outperformed Ag island films (dry medium - 785 nm laser line). In order to overcome the challenges of ethephon detection by the SERS technique, several parameters were varied: pH, salt addition, laser line excitation, time dependence, direct powder dissolution, and different types of substrates (solid and colloidal dispersion). Furthermore, a theoretical approach was carried out (density functional theory and charge-assisted fragment interaction).image (AU)

• FAPESP's process: 18/22214-6 - Towards a convergence of technologies: from sensing and biosensing to information visualization and machine learning for data analysis in clinical diagnosis
• Grantee: Osvaldo Novais de Oliveira Junior
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 21/02746-6 - Surface-enhanced Raman Scattering (SERS): pesticide detection and adsorption mechanism
• Grantee: Isabela Bianchi Carvalho
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 17/15019-0 - Combination of confocal fluorescence microscopy and surface-enhanced Raman scattering techniques: interaction, detection, and quantification of molecules of interest in biomimetic system.
• Grantee: Cibely da Silva Martin Sonvesso
• Support Opportunities: Scholarships in Brazil - Post-Doctoral