A piezoelectric sensor with a molecularly imprinted synthetic polymer receptor was developed. A plant hormone, indole-3-acetic acid (IAA) was used as the model target molecule, and an IAA-imprinted polymer was coated onto a 9 MHz AT-cut quartz crystal microbalance. The sensor showed a selective response and gave a linear relationship between frequency shift and amount of IAA in the range from 10 to 200 nmol.Keywords: Quartz crystal microbalance, Molecular imprinting, Arti®cial receptor, Plant hormoneBiosensors are widely applied to the measurement and the detection of biological compounds in analytical ®elds [1,2]. The recognition elements, consisting of biomolecules, have an excellent molecular recognition ability, but have some restrictions in use such that biosensors could be used only for compounds which are soluble in aqueous solution and sometimes could not be used repeatedly. For the purpose of developing a sensor system which could measure samples dissolved in organic solvents and has a durable recognition element, a synthetic polymer receptor prepared by molecular imprinting was used as a recognition element for a quartz crystal microbalance (QCM) in this study. Molecular imprinting is template polymerization for synthesizing complementary binding sites for given molecules with tailor-made fashion [3±12]. The common application of a molecularly imprinted polymer has been the af®nity media for liquid chromatography by using its speci®c recognition ability.QCM has been used as piezoelectric biosensors immobilized with antibodies [13], DNAs [14] and lipids [15]. Also, QCM sensors with arti®cial receptors as recognition materials have been reported: the recognition cavity of TiO 2 ultrathin ®lm by the repeated immersion of titanium oxide gel with the existing of template [16], chiral recognition sites in dipeptide crystals imprinted to amino acid derivative [17], and polyurethane-based imprinted polymer [18]. QCM can simply detect a mass change on the surface of the electrode as a frequency shift and has a sensitivity at the nanogram level. QCM has been widely used in the analytical ®eld, and is, therefore, employed as the transducer in this work.We report that imprinted polymers for indoleacetic acid (IAA), which is a plant hormone and acts as a plant growth factor, were prepared with N YN -dimethylaminoethyl methacrylate as the functional monomer and the polymers showed high af®nity and selectivity for IAA (Scheme 1) [7]. Employing this system an IAA-imprinted polymer-coated QCM sensor was prepared, and the application of the molecularly imprinted polymer to the recognition element is demonstrated.Three IAA-imprinted polymer coated-QCMs and corresponding blank polymer-coated QCMs were prepared. As shown in Figure 1, frequency shifts in IAA-imprinted polymer coated-QCM according to the amounts of IAA added were observed and a linear relationship was obtained from 10 nmol to 200 nmol of IAA. The coef®cient variation among the three sensors was 9.0 % by the calculation from the slope of the three wor...
The antitumor active compound 5-fluorouracil (5-FU) was used as a target molecule and 5-FU-imprinted polymers were synthesized using 2,6-bis(acrylamido)pyridine and/or 2-(trifluoromethyl)acrylic acid as functional monomers. The 5-FU-imprinted polymers showed a higher affinity for 5-FU than that for 5-FU derivatives. By using both functional monomers simultaneously, the affinity and separation for 5-FU were improved.
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