Organophosphate detection using silver nanoparticles and molecularly imprinted polymer (MIP)
Tuesday, 7th December 2021, starting at 5:00 pm.
https://teams.live.com/meet/95330526856279
Abstract:-
Phorate, chlorpyrifos, and malathion are hazardous pesticides used to control weeds, pests, insects, or mosquitoes. Their presence in residual amounts causes harm to human health and the environment. Various traditional techniques are available for the detection of these molecules, but these techniques lack specificity. So there is thrust to have a specific sensor for the detection of pesticide residues. A depth understanding of the interaction of pesticides with suitable sensing molecules is deeply required before sensor fabrication. The given work introduces a depth understanding of the interaction of sulfur-containing organophosphates in solution and on the surface with a suitable sensing substrate. The interaction of three organophosphates, namely phorate, chlorpyrifos, and malathion containing the P=S group with borohydride stabilized silver nanoparticles, was analyzed in solution. The colorimetric changes are corroborated with UV-visible absorption studies, changes in particle size, and zeta potential. This effect persists in the presence of NaCl solution also. The chlorpyrifos and malathion do not show significant interactions with uncapped nanoparticles over time, while phorate undergoes degradation due to the scission of the S–CH2 linkage. A reaction mechanism wherein a silver and sulfur (Ag/S) complex is formed, which is in agreement with Raman spectroscopic studies, is proposed. The orientations of phorate near Ag nanoparticles are discussed from the adsorption energy calculation using density functional theory.
To study the interaction of pesticides on the surface, we first created SAMs with four different functionalities and studied the adsorption of these pesticides in QCM-D, which is very precise to check the interaction of analyte molecules on the surface by monitoring real-time adsorption in terms of mass change. The interaction of two organophosphates, phorate, and malathion, was studied on the silica surface, functionalized by four different silane coupling agents, i.e., n-propyltrimethoxy silane (PTMS), octyltrimethoxy silane (OTMS), 3- (trimethoxysilyl) propyl methacrylate (TMSPMA), and 3- (triethoxysilyl) propionitrile (TESPN). The surface was characterized by measuring the contact angle and surface energy, Raman spectra, and atomic force microscopy studies. A kinetic model is developed and fitted with the experimental data. The equilibrium adsorbed mass is fitted for the modified BET adsorption isotherm and n (number of layers adsorbed), Tm (monolayer adsorbed mass), KS (equilibrium constant for the first layer of pesticide adsorbed on functionalized silica surface), and KL (equilibrium constant for further adsorbed layers). The results show that TMSPMA functionalized surface being more hydrophilic among all surfaces adsorbs hydrophobic pesticides molecules more uniformly.
These surface functionalities do not provide specificity for a particular molecule as they can interact with different molecules having the same terminal groups. To achieve more selectivity, MIP was synthesized using TMSPMA as a functional monomer by sol-gel techniques. The MIP was coated on QCM-D quartz crystal, and adsorption of the template molecule, i.e., phorate and malathion, are studied. It is found that the synthesized MIP shows significant binding with template molecules while non-imprinted polymer (NIP) does not show any interaction. It confirms that the synthesized sensor can detect pesticide molecules. QCM sensor is also checked for its specificity and repeatability. The sensor is highly selective among the studied pesticides, and MIP shows good repeatability when coated on the QCM crystal surface. The synthesized MIP is validated using HPLC and shows a recovery rate of around 95%. Keywords: Organophosphates, QCM-D, Adsorption, MIP, Diffusion-Kinetic model