Surface acoustic wave sensor based on molecularly imprinted polymer for highly sensitive detection of glyphosate

Glyphosate (Gly) is a broad-spectrum herbicide extensively used for weed control in grain crop production. Its overuse has led to several issues, including contamination of surface water, decreased soil fertility, and incorporation into food chains, resulting in toxic effects on human health. To address these issues, we developed a new reliable method to selectively and sensitively detect glyphosate in surface waters based on a surface acoustic wave (SAW) mechanism integrated with molecularly imprinted polymer (MIP) based technology. The sensing layer derived from chitosan was obtained in the presence of Gly as template molecule by cross-linking with glutaraldehyde. The chitosan-based polymers were characterized through different techniques, such as scanning and transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, revealing the morphological and structural features of the polymer matrix. The developed MIP-SAW sensor showed high affinity toward Gly in buffer solutions, resulting in a sensitivity of 29.7°/ppb and a limit of detection of 0.4 ppb. Glyphosate molecules bind rapidly to specific recognition sites found at the interface between the MIP and the aqueous phase, evidencing surface-dependent interactions that cause a rapid change in the phase shift response. Moreover, the MIP-SAW sensor was tested in real water samples in the 0.01 ppb - 10 ppb glyphosate concentration range. The response of the MIP-SAW sensor was evaluated, resulting in a sensitivity of 1°/ppb, with an excellent limit of detection of 0.12 ppb. Selectivity studies further demonstrated the absence of interference with phosmet, chlorpyriphos, and glufosinate species.