National University of Singapore,
Keywords: sensor, polymer, molecular imprinting, pesticides
Summary:Molecularly Imprinted Polymers (MIP) have been widely applied as sensors for many analytes. The basic principle of MIP is that the templates embedded in polymer film are removed leaving the polymer film with molecularly imprinted cavities. Such a polymer film is called MIP. The analytes could include chemical molecules, biological molecules, proteins, antibodies, bacterial, virus, etc. Currently, MIPs are prepared through an in-situ but diffusion-dependent inclusion of template molecules into polymers during polymerisation. During the polymerization process, the dissolved monomers become solid phase polymers while the template molecules are in aqueous solution (liquid phase). Template molecules in the liquid phase may have difficulty to diffuse and be entrapped into the solid polymer phase. Accordingly, many template molecules may still remain in the solution while only a few of them are in the matrix of polymer. This limits the available imprinted molecular cavities in the prepared MIP-based sensor. There is therefore a need for an improved method of making a molecularly imprinted polymer sensor. The present investigation seeks to address these problems, and/or to provide an improved method of making a molecularly imprinted polymer sensor. A new selective and sensitive sensor based on molecularly imprinted poly(vinylidene fluoride) (PVDF) polymer for the detection of methyl parathion (MP), a ubiquitous highly hydrophobic pesticide that is commonly used as a simulant of chemical threat agents. The PVDF-based sensor was prepared using the molecular imprinting method with a pre-polymerized PVDF instead of traditional in-situ or post- polymerized ones to avoid harsh and tedious polymerization conditions. The results show that the prepared PVDF-based sensor indeed showed high selectivity towards MP against other pesticides such as diethyl phosphoramidate, dicrotophos, 2,4,5-trichlorophenoxyacetic acid, and terephthalic acid. The specificity and selectivity of the prepared MIP were further verified with detection of the analyte in spiked water samples. Molecular recognition in MIP is attributed to complementary binding sites with same or similar size, shape, and functionality to imprint molecules. In addition to size and shape of the imprinted cavities, the developed MIP-based sensors could exhibit high selectivity and sensitivity mainly due to dipole-dipole interaction, hydrophobic interaction and van der Waals interactions with the template MP molecules. The advantage of the molecularly imprinted polymer sensor made from the method developed is that it has good selectivity, reliability and high sensitivity to the target molecules. Further, the molecularly imprinted polymer sensor made from the developed method allows for fast detection of the target molecules. The method is also a low-cost and simple preparation method for making the molecularly imprinted polymer sensor. Detection of PTM was demonstrated on the fabricated MIP-based quartz crystal microbalance sensor. The linearity of the calibration curve was as good as 0.99997. From the calibration curve, limit of detection (LOD) and limit of quantitation (LOQ) were determined to be 68.0 (S/N=3) and 226.8 nM (S/N=10), respectively.