Indirect Quantification of Glyphosate by SERS Using an Incubation Process With Hemin as the Reporter Molecule: A Contribution to Signal Amplification Mechanism

Abstract

The indirect determination of the most used herbicide worldwide, glyphosate, was achieved by the SERS technique using hemin chloride as the reporter molecule. An incubation process between hemin and glyphosate solutions was required to obtain a reproducible Raman signal on SERS substrates consisting of silicon decorated with Ag nanoparticles (Si-AgNPs). At 780 nm of excitation wavelength, SERS spectra from hemin solutions do not show extra bands in the presence of glyphosate. However, the hemin bands increase in intensity as a function of glyphosate concentration. This allows the quantification of the herbicide using as marker band the signal associated with the ring breathing mode of pyridine at 745 cm−1. The linear range was from 1 × 10−10 to 1 × 10−5 M and the limit of detection (LOD) was 9.59 × 10−12 M. This methodology was successfully applied to the quantification of the herbicide in honey. From Raman experiments with and without silver nanoparticles, it was possible to state that the hemin is the species responsible for the absorption in the absence or the presence of the herbicide via vinyl groups. Likewise, when the glyphosate concentration increases, a subtle increase occurs in the planar orientation of the vinyl group at position 2 in the porphyrin ring of hemin over the silver surface, favoring the reduction of the molecule. The total Raman signal of the hemin-glyphosate incubated solutions includes a maximized electromagnetic contribution by the use of the appropriate laser excitation, and chemical contributions related to charge transfer between silver and hemin, and from resonance properties of Raman scattering of hemin. Incubation of the reporter molecule with the analyte before the conjugation with the SERS substrate has not been explored before and could be extrapolated to other reporter-analyte systems that depend on a binding equilibrium process.

Food Safety Issues in the Oltrepò Pavese Area: A SERS Sensing Perspective

“…An increasingly body of literature is available on the use of SERS for glyphosate detection both as a single detection technique as well as part of a combined approach [43][44][45]. We point out that the majority of research papers [39,41,42,[44][45][46][47][48][49][50][51] illustrates studies on Gly detection by using Ag nanoparticles as an enhancing active medium, and bench-top Raman instrumentation to perform the measurement, reaching Limits Of Detection (LODs) generally below the MRLs imposed by the European Union (EU). In contrast, refs [52,53] present two different research works exploiting, respectively, Au-Ag nanochains for a novel anti-interference, indirect detection, reaching a LOD of 5 µg/L (5 ppb) and Au nanoparticles in a needle tip enrichment approach with an estimated LOD of 7.5 nmol/L (≈1.3 ppb) (see Figure 3 for an illustration of the sensing mechanism and related SERS results).…”

A review of cardiac troponin I detection by surface enhanced Raman spectroscopy: Under the spotlight of point-of-care testing

“…The former occurs when the excitation laser is tuned into or near an electronic transition of the molecule that is attached on a SERS substrate. Under this condition an improvement of the conventional resonance Raman scattering of the molecule is induced by its proximity to the substrate ( López-Castaños et al, 2020 ; Moldovan et al, 2022 ). The PL-SERS arises from the coupling of certain normal modes of the adsorbate with internal resonant excitations of small metal clusters ( Román-Pérez et al, 2014 ).…”

A photo-responsive p-Si/TiO2/Ag heterostructure with charge transfer for recyclable surface-enhanced Raman scattering substrates

“…Lastly, this TiO 2 /Ag heterostructure SERS substrate was used to detect glyphosate (N-(phosphonomethyl) glycine, C 3 H 8 NO 5 P: Gly), an effective broad-spectrum systemic herbicide increasingly used for the control of undesirable weeds in cultures. [25][26][27][28][29][30][31] In this study, a TiO 2 thin film was prepared by a sol-gel method and Ag nanoflowers were then electrodeposited on it. Compared with the typical reported preparation methods, such as hydrothermal synthesis, magnetron sputtering and vacuum evaporation, sol-gel is considered an effective and low-cost approach to obtain high performance films without complex equipment and strict conditions.…”