There is a global debate and concern about the use of glyphosate (Gly) as an herbicide. New toxicological studies will determine its use in the future under new strict conditions or its replacement by alternative synthetic or natural herbicides. In this context, we designed biomimetic polymer sensing layers for the selective molecular recognition of Gly. Towards this end, complementary surface acoustic wave (SAW) and electrochemical sensors were functionalized with polypyrrole (PPy)-imprinted polymer for the selective detection of Gly. Their corresponding limits of detection were on the order of 1 pM, which are among the lowest values ever reported in literature. The relevant dissociation constants between PPy and Gly were estimated at [K_d1 = (0.7 ± 0.3) pM and K_d2 = (1.6 ± 1.4) µM] and [K_d1 = (2.4 ± 0.9) pM and K_d2 = (0.3 ± 0.1) µM] for electrochemical and gravimetric measurements, respectively. Quantum chemical calculations permitted to estimate the interaction energy between Gly and PPy film: ΔE = −145 kJ/mol. Selectivity and competitivity tests were investigated with the most common pesticides. This work conclusively shows that gravimetric and electrochemical results indicate that both MIP-based sensors are perfectly able to detect and distinguish glyphosate without any ambiguity.

Surface acoustic waves (SAW) devices are used in several domains varying from telecommunication and mechanics to chemical and biological sensing. Their ability to function in either liquid or gaseous environments make them devices of choice for the detection of several types of analytes (DNA, antibodies/antigens, gases, pesticides, heavy metals …) in real time and without labeling. Compared to other chemical and biological sensors, the SAW ones are highly sensitive and can achieve very low limits of detection. Among the large variety of acoustic devices, SAW sensors are the most promising ones, as their operating frequencies can be varied from several hundred MHz to a few GHz. However, they are still the subject of constant development; therefore, simulation becomes a powerful tool to design optimised structure for highly sensitive devices. This study concerns 3D Finite Element Method (FEM) simulation of SAW sensors using COMSOL Multiphysics software. A SAW delay line was designed on 36°lithium tantalate (LiTaO₃) piezoelectric substrate. Interdigital transducers (IDTs) were patterned in Cr/Au (20 nm/80 nm) layers with the same periodicity of λ = 40 μm. A metallized Cr/Au (20 nm/80 nm) sensing area of 80 µm length separates the input and output IDTs. The corresponding frequency is thus of order of 104 MHz. Simulations were made on well-known structure to define a model that can account for and predict the electrical behaviour of SAW transducers for the future optimisations. The results show good agreement between COMSOL numerical simulation and experimental S21 spectra. Accordingly, we can use the built model for simulations intended to optimize the structure of devices, mainly for increasing their sensitivity.

Modeling a Surface Acoustic Wave (SAW) sensor response as a chemosensor and not only as just an electronic transducer was performed with COMSOL Multiphysics. For this study, the SAW’s sensing area was functionalized with an ionic imprinted polymer (IIP), designed for the selective detection of lead ions. The idea consists in subdividing the IIP into elementary blocks whose physical properties can be modified separately. Three configurations have been envisaged: the IIP before and after lead ions extraction and the non-imprinted polymer (NIP). The generation of shear-horizontal waves on LiTaO₃ piezoelectric substrate is confirmed by recording the displacement amplitude versus time, according to the three space directions. The sensors sensitivity is estimated from the delays induced by the incorporation of the lead ions in the IIP layer. To the best of our knowledge, this approach has never been presented in the literature.