Graphite Oxide and Gold Nanoparticles as Alternative Materials in the Design of a Highly Sensitive Electrochemical Sensor for the Simultaneous Determination of Biological Species.

New aspects related to electrochemical performance of modified carbon paste electrodes (CPE) of high analytical performance are presented in this work. We studied whether the functionalisation of graphite powder with oxygenated functional groups (graphite oxide, GrO) could affect the electrochemical features of a classical CPE. By introducing oxygen termination over the graphite surface, a remarkable improvement in electrochemical performance was verified, including enhancement of analytical signals and charge transfer kinetics, as demonstrated from electrochemical characterisation assays conducted by cyclic voltammetry and electrochemical impedance spectroscopy towards the potassium hexa-cyanoferrate (II/III) probe. In addition, a positive effect was noted from the anchoring of Au nanoparticles on GrOPE. In analytical terms, two biologically relevant molecules were simultaneously determined using the proposed modified electrode based on GrO and AuNPs: epinephrine (EP) and uric acid (UA). Using differential pulse voltammetry (DPV), wide linear concentration ranges were founded for the analytical curves of EP and UA, and the limits of detection of 1.0×10−7 mol L−1 (EP) and 5.0×10−8 mol L−1 (UA) were predicted, respectively. The designed electrochemical sensor showed excellent precision of measurement and appropriate applicability for the analysis of biological fluids. [ABSTRACT FROM AUTHOR]