Glyphosate is one of the most effective herbicides and
is extensively
used in agriculture to improve crop production. However, its toxicity
and carcinogenicity stimulate the development of potent, rapid, and
highly selective sensors for glyphosate. In this study, we have successfully
developed a rational and effective method for detecting glyphosate
concentrations in the nanomolar range through luminescence enhancement.
For this purpose, we synthesized NH2-MIL-88B (Fe) (MIL
= Material Institute Lavoisier) metal–organic framework (MOF)-based
nanocrystals (NCs) using the hydrothermal method and applied it for
glyphosate detection in an aqueous medium. The MOF NCs contain coordinative
ligands (2-aminoterephthalic acid) and metal clusters. The Fe clusters
act as luminescence quenchers, suppressing emission from the MOF due
to photoinduced electron transfer (PET) from the ligand to Fe3+ ions. The phosphate group of glyphosate competes with the
carboxylate of the ligand in the MOF. As a result, the coordination
between ligand molecules and Fe metal clusters in the MOF weakens,
causing the ligand molecules to separate from the Fe cluster. This
process diminishes the PET and regenerates the ligand emission at
450 nm. The luminescence enhancement exhibits high selectivity toward
glyphosate and shows minimal interference from various pesticides
and metal ions. The limit of detection was calculated as 198 nM, and
the performance of the detection probe was evaluated in drinking water.
Finally, MOF NCs-coated circular paper strips were prepared and successfully
applied to detect glyphosate at femtomolar concentrations.