Development and validation of an integrated microfluidic device with an in-line Surface Enhanced Raman Spectroscopy (SERS) detection of glyphosate in drinking water.

Glyphosate, also known as N-(phosphonomethyl)glycine, is one of the most widely used herbicides in the world. However, the controversy surrounding the toxicity of glyphosate and its main breakdown product, aminomethylphosphonic acid (AMPA), remains a serious public concern. Therefore, there is a clear need to develop a rapid, sensitive and automated alternative method for the quantification of glyphosate and AMPA. In this context, surface enhanced Raman spectroscopy (SERS) coupled with a microfluidic system for the determination of glyphosate in tap water was developed, optimized and validated. The design of the microfluidic configuration for this application was built constructed to integrate the synthesis of the SERS substrate through to the detection of the analyte. To optimize the microfluidic setup, a design of experiments approach was used to maximize the SERS signal of glyphosate. Subsequently, an approach based on the European guideline document SANTE/11312/2021 was used to validate the method in the range of 78-480 µg/L using the normalized band intensities. The limit of detection and quantification obtained for glyphosate were 40 and 78 µg/L, respectively. Recoveries were in the range 76-117%, while repeatability and intra-day reproducibility were ≤17%. Finally, the method was also tested for the determination of AMPA in tap water matrix and for the simultaneous detection of AMPA and glyphosate.

Understanding chemical interaction between phosphonate-derivative molecules and a silver surface cluster in SERS: a combined experimental and computational approach.

The interaction between phosphonate functions and a silver surface cluster is investigated using Surface-Enhanced Raman Spectroscopy (SERS). Changing the functional group (methylphosphonic acid based molecule) by studying the effect of protonation, methylation and substitution of the side chain with amine and carboxylate functions enabled us to modulate the chemical interactions between the different functions and the metal cluster. We find that the adsorption energy of the methylphosphonic acid decreases with the protonation, the methylation processes and the substitution of the side chain. In all cases, only the deprotonated phosphonate forms are SERS active. To understand how the molecules interact with the nanoparticle, the electronic structure, adsorption energies and Raman spectra were computed for molecules adsorbed on a 20 atom silver cluster representing a nanoparticle surface. The qualitative agreement between computed static Raman spectra and experimental SERS spectra makes it possible to determine stable geometries of the analyte-silver cluster complexes and to characterize the adsorption modes. The findings presented here provide a framework for designing analytical developments based on SERS for simultaneous detection of phosphonated molecules, including pesticides such as glyphosate, creating practical opportunities in key areas such as environmental and water resource in situ monitoring.