A glassy carbon electrode modified with carbon nanotubes and reduced graphene oxide decorated with platinum-gold nanoparticles for voltammetric aptasensing of urea

This article reports on a novel aptamer-based platform for the quantitation of urea by using an aptamer with high affinity and selectivity for urea. The surface of a glassy carbon electrode (GCE) was modified by drop casting a cocktail consisting of carbon nanotubes and reduced graphene oxide (rGO) decorated with platinum-gold nanoparticles. The urea aptamer was then immobilized on the nanocomposite via covalent conjugation. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to trace the modification of the GCE. Binding of urea caused the aptamer to be folded, and this result in an inhibition of the interfacial charge transfer rate when using hexacyanoferrate as an electrochemical redox probe. The change in redox current was quantified by differential pulse voltammetry, typically at a working voltage of 0.22 V vs. Ag/AgCl. The assay has a 1.9 pM detection limit, and the response is linear up to 150 nM concentration of urea. The superior selectivity and affinity of aptamer-modified GCE makes it a most useful tool for analysis of urea present in very low concentrations.