Abstract
Piezoelectric quartz crystals and analogous gold substrates were electrochemically coated with molecularly imprinted polypyrrole films for pulsed amperometric detection (PAD) of clofibric acid, a metabolite of clofibrate. Cyclic voltammetry data obtained during polymerization and deposited weight estimations revealed a decrease of the polymerization rate with increasing clofibric acid concentration. XPS measurements indicated that clofibric acid could be removed after imprinting with an aqueous ethanol solution, which was further optimized by using PAD. Zeta potential and contact angle measurements revealed differences between molecularly imprinted (MIP) and non-imprinted polymer (NIP) layers. Binding experiments with clofibric acid and other substances showed a pronounced selectivity of the MIP for clofibric acid vs. carbamazepine, but the response of MIP and NIP to 2,4-dichlorophenoxyacetic acid was higher than that for clofibric acid. A smooth surface, revealed by AFM measurements, with roughness of 6–8 nm for imprinted and non-imprinted layers, might be a reason for an excessively low density of specific binding sites for clofibric acid. Furthermore, the decreased polymerization rate in the presence of clofibric acid might not result in well-defined polymer structures, which could be the reason for the lower sensitivity.
Highlights
The preparation of cross-linked synthetic polymers with specific binding sites in the presence of template molecules is called molecular imprinting
Binding tests under pulsed amperometric detection (PAD) conditions were done with 30 μM solutions of 2,4-D and CBZ for 10 min and compared with the results of molecularly imprinted (MIP) and non-imprinted polymer (NIP) binding tests with clofibric acid under the same conditions
The results show higher responses to the clofibric acid solution for MIPs than for NIPs, but the amount of non-specific binding is high
Summary
The preparation of cross-linked synthetic polymers with specific binding sites in the presence of template molecules is called molecular imprinting. A following lower potential reduces the polymer and the negative ions are expelled from the polymer, which results in cathodic current [27,28] This method was used for neutral molecules by Ramanaviciene et al in combination with conducting imprinted polymers for the detection of caffeine and bovine leukemia virus glycoproteine gp51 [29,30]. The binding of the target molecule to the imprinted sites was detected by application of several potential steps and the sensor response was obtained by the peak difference of the current response. The advantage of this method is the possibility to detect the binding of electroinactive substances to imprinted sites In this project, clofibric acid was used as a template. The aim had been to elucidate how efficiently the electropolymerization of polypyrrole could be used to obtain a MIP-based sensor for clofibric acid
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