Nanostructured Fe3O4 satellite gold nanoparticles to improve biomolecular detection

Fe3O4 satellite gold nanoparticles (Fe3O4@Au) have proved to be very useful in biomedical and technological applications because of their unique optical, magnetic, and catalytic properties. The electrocatalytic properties of Fe3O4@Au nanoparticles enable them to be used as mediator agents during the redox of electroactive species. In this study, Fe3O4@Au were synthesized in the presence of generation four polyamidoamine (PAMAM G4). The Fe3O4@Au nanoparticles were immobilized by layer-by-layer (LbL) technique to develop dopamine sensors by alternately depositing layers of Fe3O4@Au nanoparticles and poly(vinyl sulfonic acid) as polyanionic polymer onto an indium tin oxide electrode. The electrochemical performances of the indium tin oxide/poly(vinyl sulfonic acid) and indium tin oxide/gold nanoparticle/poly(vinyl sulfonic acid) electrodes were also investigated for comparison. The modified electrodes were characterized using ultraviolet–vis absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and cyclic voltammetry. The electrocatalytic properties of the iron oxide/gold nanoparticles configured throughout the indium tin oxide-iron oxide/gold/poly(vinyl sulfonic acid) architecture promoted a dopamine oxidation process at a potential of 0.30 V, which is lower compared with those observed for the other sensors. The dopamine sensor provided linear responses to dopamine in the 4–100 μM range with detection limit and quantification values as 3.94 × 10−8 M and 15.5 × 10−8 M, respectively. Furthermore, the main interferents to dopamine detection were ascorbic and uric acids, whose cyclic voltammograms showed oxidation peaks that, were displaced by 0.2 and 0.39 V in their respective binary mixtures with dopamine. The immobilized iron oxide/gold nanoparticles in the layer-by-layer-fabricated films exhibited an efficient electron transfer, which could be useful when such films are combined with other conjugated materials to detect electroactive species that are highly relevant in medical applications.