Fully graphene-based electrode platforms for biosensing applications

A simple, fast, and reproducible analyte detection using low amounts of solution is nowadays possible thanks to the presence on the market of disposable screen-printed electrodes: they are widely employed in academic research as well as in industrial applications, as they are suited for a wide range of purposes. They are available in different geometries, on flexible or solid supports and with working electrodes consisting of conventional and non-conventional materials; in particular, different nanosized materials can be included in the printed ink or added as a coating afterwards. Among the variety of nanomaterials proposed to impart effectiveness to the sensor response, graphene derivatives are increasingly exploited in electrochemical biosensing, since their nanosized dimensions allow a great number of oxidized residues to be well exposed to the surrounding environment; these moieties are responsible for the activation of electrocatalytic processes toward several species, i.e. a decrease of the oxidation or reduction potentials of the analyte with respect to pristine carbon electrodes. To fully exploit the electrocatalytic performance of this nanosized material, we developed flexible, self-standing three-electrode cells entirely made of graphene. They were realised from pristine graphene paper (G-paper), a flexible, electrically conductive, paper-like material which has a large surface area, high porosity and can be easily obtained in different shapes. We demonstrated that G-paper electrodes can be successfully employed in electrochemical sensing, thanks to electrochemical tests with a benchmark redox species. In addition, their electrocatalytic properties were studied towards the detection of the two main products of enzymatic reactions, namely nicotinamide adenine dinucleotide (NADH), a co-factor for many dehydrogenase-type enzymes, and of H₂O₂, a product of many oxidase-based enzymatic reactions. These tests demonstrate the possible advantages in the use of these new devices with respect to those present on the market.