Voltammetric aptamer-based switch probes for sensing diclofenac using a glassy carbon electrode modified with a composite prepared from gold nanoparticles, carbon nanotubes and amino-functionalized Fe3O4 nanoparticles

The authors describe an aptamer based assay for the model analyte diclofenac (DCF). It is based on the use of amino-functionalized magnetite and gold nanoparticles (Fe3O4/AuNPs) that were used to decorate carbon nanotubes (CNTs) to form a highly conductive film on the surface of a glassy carbon electrode. An amino-modified DNA capture probe (ssDNA1) was placed on the Fe3O4/AuNPs using glutaraldehyde as the linker. A DCF-specific aptamer (referred to as ssDNA2)acting as the detection probe was then attached to the surface of the modified electrode via hybridization. On addition of DCF, the conformation of the aptamer undergoes a change from a random coil structure to a rigid tertiary structure (like a pocket). This change can be traced by measuring the decrease of the current observed by differential pulse voltammetry using hexacyanoferrate as a redox probe, typically at a working voltage of 0.22 V vs. Ag/AgCl. The method has a 3.4 fM detection limit and two linear responses that cover the 0.01 to 1 pM and 10 to 1300 pM DCF concentration ranges.