Polyelectrolyte-Enzyme Assemblies Integrated into Graphene Field-Effect Transistors for Biosensing Applications

Graphene field-effect transistors with the integration of enzymes are cutting-edge devices in medical diagnostics because they display inherently amplified, ultrasensitive, label-free, and real-time response, in addition to operating in aqueous samples at very low voltage. Precise and rational surface engineering of graphene to integrate recognition elements preserving the biological activity without the disruption of the graphene aromatic structure is of paramount importance. In this chapter, we describe the development of biosensors by the integration of enzymes such as urease and arginase onto reduced graphene oxide (rGO) FETs by using the layer-by-layer (LbL) nanoconstruction technique. This non-covalent approach avoids the alteration of graphene´s chemical structure and guarantees the maintenance of the enzymatic activity and the accessibility to the active sites. The signal transduction mechanism is based on the ability of the enzymes to selectively perform chemical transformations and prompt local pH changes near the graphene surface, which is sensitively detected. First, the integration of urease and polyethyleneimine (PEI) on rGO that shows great selectivity and sensitivity for the detection of urea is described. This bioelectronics test shows a limit of detection (LOD) of 1 μM urea and a linear range of up to 1 mM. Furthermore, two different enzymes can be integrated on rGO for cascade biosensing. We describe the integration of arginase and urease on the rGO FET sensing surface via LbL assembly for the detection of L-arginine through a cascade enzymatic reaction. These transistors can monitor L-arginine in the 10 – 1000 μM linear range with a LOD of 10 μM, and show stereospecificity and high selectivity in the presence of non-target amino acids.