Rapid on-site monitoring of pesticide residues with MIP sensors
Creators: name: Al Kobaisi, Mohammad
Publisher: name: RMIT University
Year: 2024

description: Molecularly imprinted polymer coated quartz crystal (QCM-MIP) sensors were fabricated for the detection of 'iprodione' in wine and grape juice liquid phases. A set of polymers was templated with iprodione and pyrimethanil to study the imprinting process and the properties of the imprinted and non-imprinted polymers (NIP). The effect of solvent type and ratio, functional monomers (FMs), and templates on the polymer properties was studied. Porogenic solvents produced mesoporous polymers with high surface areas of up to 510 m2/g as measured using the BET method. Non-porogen solvents produced macroporous polymers with much lower surface areas between 50 - 150 m2/g. Low solvent ratios (~5%) produced glassy polymers with very low surface areas, while high solvent ratios (~95%) produced polymer microspheres. Between the above limits porous polymeric systems are produced. Nitrogen adsor ption, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used to characterize the morphology and microstructure of the polymers. <br><br>The comparison of TGA decomposition profiles of the MIPs and NIPs showed higher stability for the MIPs when [sigma-sigma] interaction between the template - FM was utilized in the imprinting process resulting in higher geometrical order due to the [sigma-sigma] stacking. <br><br>Iprodione had a minimal effect on the EGDMA - MAA polymer system when compared to pyrimethanil. The stronger pyrimethanil - MAA interactions caused the monomers to associate closely around the template in the pre-polymerization solution, and reduces the pore sizes of the EGDMA - MAA polymer to the minimum possible in the mesopore range. It was observed that iprodione leaves stronger imprinting effect when aromatic FMs are used. This effect was maximised using FMs with larger aromatic systems. <br><br>The stability of the porous system in EGDMA - DVB - 4VPy polymers was examined at high temperatures, no significant changes were observed based on BJH pore size distribution and FTIR up to 200°C. It was observed in the iprodione adsorption isotherms studies in model and real solutions that iprodione adsorption is strongly influenced by the nature of the medium and although imprinting improved the polymers selectivity and capacity, it had smaller role in the adsorption process. <br><br>The MIP and NIP adsorption thermodynamics clarified the polymer structure heterogeneity showing that imprinting produced larger hydrophobic segments in the polymer network. <br><br>The EGDMA - DVB - 4VPy MIP and NIP were applied to QCM using sandwich method. Pre-polymerization solution volumes of 0.5 - 1 µL were used to produce coatings which caused approximately 2 kHz shift in the QCM resonator frequency, while maintaining a high quality factor. The polymer films response to several aqueous media and to iprodione solution in these media was studied. The results showed a novel means to investigate water clustering in contact with solids and adsorbed species exchange on the surface in the adsorption process. Similar to iprodione adsorption in the bulk studies, iprodione sensing using the QCM-MIP system showed great sensitivity to the medium composition. In a controlled medium environment the method shows a near-linear range between 5 and 100 ppm iprodione in white grape juice, with relative standard deviations between 10 and 4%. <br>