Abstract
The development of methodologies to sense glyphosate has gained momentum due to its toxicological and ecotoxicological effects. In this work, a red-emitting and polymerizable guanidinium benzoxadiazole probe was developed for the fluorescence detection of glyphosate. The interaction of the fluorescent probe and the tetrabutylammonium salt of glyphosate was studied via UV/vis absorption and fluorescence spectroscopy in chloroform and acetonitrile. The selective recognition of glyphosate was achieved by preparing molecularly imprinted polymers, able to discriminate against other common herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (dicamba), as thin layers on submicron silica particles. The limits of detection of 4.8 µM and 0.6 µM were obtained for the sensing of glyphosate in chloroform and acetonitrile, respectively. The reported system shows promise for future application in the sensing of glyphosate through further optimization of the dye and the implementation of a biphasic assay with water/organic solvent mixtures for sensing in aqueous environmental samples.
Highlights
Glyphosate (GPS) is the most widely used herbicide, its use increasing exponentially after the introduction of glyphosate-resistant transgenic crops in 1996 [1–3].In the past decade, interest in methods for its determination in environmental samples has grown because of its toxicological [4] and ecotoxicological effects [5,6], as well as its occurrence in water reserves and food [7]
Because our aim is to move toward the direct sensing of GPS, we embarked on the development of a GPS-selective fluorescent probe that fulfills the application-oriented requirements of absorption in the visible spectral range and a strongly Stokes-shifted emission in the red-to-near infra-red (NIR) range, so that instrumentation can be kept simple
In contrast to what has been previously realized in the few direct approaches, for instance, with a photoinduced electron transfer-type probe in the UV/vis region [30], we elaborated our concept of dimensionally small charge transfer (CT)-type fluorescent probe monomers [48] and integrated a second electron-donating unit into the fluorophore architecture, arriving at compound I (Figure 1a)
Summary
Glyphosate (GPS) is the most widely used herbicide, its use increasing exponentially after the introduction of glyphosate-resistant transgenic crops in 1996 [1–3]. Interest in methods for its determination in environmental samples has grown because of its toxicological [4] and ecotoxicological effects [5,6], as well as its occurrence in water reserves and food [7]. In 2015, the International Agency for Research on Cancer classified GPS as “probably carcinogenic to humans” [4]. The development of methodologies to detect GPS has gained relevance in recent years, especially with respect to approaches that are reasonably simple and cost-effective, and that are potentially suitable for use outside of a dedicated laboratory and closer to an actual point of need, enabling preventive action [8]. GPS is a dimensionally small, linear, aliphatic molecule bearing three protic groups, a carboxylic acid, a phosphonic acid and an amino group (Scheme 1) [9].
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