Highly sensitive and selective electrochemical paper-based device using a graphite screen-printed electrode modified with molecularly imprinted polymers coated Fe3O4@Au@SiO2 for serotonin determination

Herein, we propose a highly sensitive and selective three-dimensional electrochemical paper-based analytical device (3D-ePAD) to determine serotonin (Ser). It uses a graphite-paste electrode modified with nanoparticles coated with molecularly imprinted polymer (MIP). Fe3O4@Au nanoparticles were encapsulated with silica to create novel nano-sized MIP. Morphology and structural characterization reveal that silica imprinted sites (Fe3O4@Au@SiO2) synthesized via sol-gel methods provide excellent features for Ser detection, including high porosity, and greatly improve analyte diffusion and adsorption to provide a faster response by the MIP sensor. The template molecule was effectively removed by solvent extraction to provide a greater number of specific cavities that enhance analyte capacity and sensitivity. The 3D-ePAD was fabricated by alkyl ketene dimer (AKD)-inkjet printing of a circular hydrophobic detection zone on filter paper for application of aqueous samples, coupled with screen-printed electrodes on the paper, which was folded underneath the hydrophobic zone. The sensor was constructed by drop coating of Fe3O4@Au@SiO2-MIP nanocomposites on the graphite electrode (GPE) surface. The MIP sensor (Fe3O4@Au@SiO2-MIP/GPE) was used in the detection of Ser by linear-sweep voltammetry (LSV) in 0.1 M phosphate buffer at pH 8.0. The device exhibits high sensitivity toward Ser, which we attribute to synergistic effects between catalytic properties, electrical conductivity of Fe3O4@Au@SiO2, and significantly increased numbers of imprinted sites. Ser oxidation was observed at +0.39 V. Anodic peak currents for Ser show linearity from 0.01 to 1000 mu M (y = 0.0075 +/- 0.0049 x + 0.4071 +/- 0.0052, r(2) = 0.993), with a detection limit of 0.002 mu M (3S/N). The device provides good repeatability (% relative standard deviations; RSD) = 4.23%, calculated from the current responses of ten different MIP sensors). The device also exhibits high selectivity and reproducibility (% RSD = 8.35%, obtained from five calibration plots). The analytical performance of the device is suitable for the determination of Ser in pharmaceutical capsules and urine samples. (C) 2019 Elsevier B.V. All rights reserved.