Aptamer-based sensor for diclofenac quantification using carbon nanotubes and graphene oxide decorated with magnetic nanomaterials

In this contribution, a novel label-free electrochemical biosensor for diclofenac (DCF) detection was developed using the unique properties of acid-oxidized carbon nanotubes (CNT), graphene oxide (GO), and Fe₃O₄ magnetic nanomaterials. The GO sheets and CNT were interlinked by ultrafine Fe₃O₄ nanoparticles forming three-dimensional (3D) architectures. The characterization of the nanocomposite was studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDS), and wavelength-dispersive X-ray (WDX) spectroscopy. Initially, aminated detection probe (aptamer) was surface-confined on the CNT/GO/Fe₃O₄ nanocomposite via the covalent amide bonds formed by the carboxyl groups on the CNT/GO and the amino groups on the oligonucleotides at the 5′ end. Our constructed folding-based electrochemical sensor was used for detection of target molecule utilizing structure-switching aptamers. Signaling arose from changes in electron transfer efficiency upon target-induced changes in the conformation of the aptamer probe. These changes were readily monitored using differential pulse voltammetry technique. This sensor exhibited binding affinities ranging from 100 to 1300 pM with a low detection limit of 33 pM.