A molecularly imprinted sol-gel electrochemical sensor based on pencil graphite electrode decorated by carbon nanotubes modified with polyoxometalate-encapsulated gold nanoparticles for trace determination of Sildenafil

Sildenafil (SIL), citrate is a medicine used in the treatment of pulmonary hypertension and impotence. SIL concentrations are commonly measured by spectrophotometric and chromatographic methods [1]. Molecularly imprinted polymer (MIP) has been demonstrated as a powerful technique in designing and synthesizing some artificial receptor molecules which is based on the copolymerization of functional and cross-linking monomers in the presence of the template molecule [2]. Electrochemical methods, especially electrochemical MIP based sensors, have attracted more attention in recent years because of their recognition properties, simplicity, high sensitivity, good stability, high selectivity, low cost, fast response and real time detection. The sol-gel based MIPs possess some advantages, such as simple fabrication process, low temperature reaction condition and matrix porosity due to highly cross-linked structure [3]. Polyoxometalates (POMs) are a distinctive class of inorganic metal–oxygen clusters. The ability of POMs anions to accept various numbers electrophile species which has made these compounds very attractive in electrode modification and electrocatalytic research [4]. POMs have been under environmentally friendly conditions used to synthesize nanoparticles (NPs). Among these modifications, the attachment of gold NPs to CNTs’ sidewalls is particularly promising for novel, highly efficient electrochemical cells and photoelectronic sensor devices [5]. In this study a new, simple and disposable molecularly imprinted electrochemical sensor for the determination of SIL was developed on pencil graphite electrode (PGE) via differential pulse voltammetry (DPV). The PGEs were coated with Au NPs@POM-CNTs tri-component nanohybrids and imprinted with sol–gel respectively. The interaction between the imprinted sensor and the target molecule was also observed on the electrode by measuring the current response of 0.2 M phosphate buffer solution (PBS, pH=7) as an electrochemical probe. Several significant parameters controlling the performance of the MIP sensor were examined and optimized. Under the optimized condition calibration curve of the imprinted sensor has two linear concentration ranges from 0.001 to 0.1 µM and 0.1 to 10.0 µM with the limit of detection (LOD) of 5×10-4 µM. Finally, the modified electrode was successfully employed to determine SIL in human urine samples.