Abstract
Herein, a biosensor based on a reduced graphene oxide field effect transistor (rGO-FET) functionalized with the cascading enzymes arginase and urease was developed for the detection of L-arginine. Arginase and urease were immobilized on the rGO-FET sensing surface via electrostatic layer-by-layer assembly using polyethylenimine (PEI) as cationic building block. The signal transduction mechanism is based on the ability of the cascading enzymes to selectively perform chemical transformations and prompt local pH changes, that are sensitively detected by the rGO-FET. In the presence of L-arginine, the transistors modified with (PEI/urease(arginase)) multilayers showed a shift in the Dirac point due to the change in the local pH close to the graphene surface, produced by the catalyzed urea hydrolysis. The transistors were able to monitor L-arginine in the 10–1000 μM linear range with a LOD of 10 μM, displaying a fast response and a good long-term stability. The sensor showed stereospecificity and high selectivity in the presence of non-target amino acids. Taking into account the label-free, real-time measurement capabilities and the easily quantifiable, electronic output signal, this biosensor offers advantages over state-of-the-art L-arginine detection methods.
Highlights
L-arginine ((S)-amino-5-guanidinopentanoic acid) is the most basic amino acid and occurs widely in living organisms
A biosensor based on a reduced graphene oxide field effect transistor functionalized with the cascading enzymes arginase and urease was developed for the detection of L-arginine
We recently reported the outstanding sensitivity of electrolyte solution-gated reduced graphene oxide field effect transistor (rGO-fieldeffect transistors (FET)) towards pH changes near the reduced graphene oxide (rGO) surface exhibiting a broad linear range with a slope of 20.3 ± 0.6 μA/pH (Piccinini et al, 2017)
Summary
L-arginine ((S)-amino-5-guanidinopentanoic acid) is the most basic amino acid and occurs widely in living organisms. The enzymes arginase and urease were immobilized as recognition elements in an LbL assembly on reduced graphene oxide field effect transistors (rGO-FET), enabling a highly sensitive, precise and selective detection of L-arginine. Optimizing the LbL architecture, biosensors with a very low limit of detection (LOD) of < 10 μM, a wide linear range of 10–1000 μM and rapid response time of 180 s were obtained. Featuring these characteristics, our biosensor compares favorably with those described in the literature. Our study is the first one describing the construction of an enzymatic cascade in an LbL assembly on an rGO-FET, paving the way for other sequential enzymes to potentially be applied as cascading recognition elements in biosensors
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