A free-standing electrochemical sensor based on graphene foam-carbon nanotube composite coupled with gold nanoparticles and its sensing application for electrochemical determination of dopamine and uric acid

In this study, a free-standing electrochemical sensor based on 3D graphene foam (GF) with dense carbon nanotubes (CNTs) and gold nanoparticles (GNPs) was developed for the first time. The structure of this hybrid electrode (GF/CNTs/GNPs) was observed by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and transmission electron microscopy (TEM), and its electrochemical properties was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The obtained sensor displayed outstanding electrocatalytic activity toward dopamine (DA) and uric acid (UA) compared with the commercial unmodified glass carbon electrode. Detection of DA and UA with the presented sensor yielded remarkable sensitivity of 12.72 μA μM^{− 1} cm^{− 2} and 3.36 μA μM^{− 1} cm^{− 2}, the low detection limits of 1.36 nM and 33.03 nM (S/N = 3), with wide linear range of 0.10–48 μM and 0.50–60 μM, respectively. Furthermore, quantification of DA in brain tissue and UA in human urine was realized and the results were found in good agreement with those obtained by using high performance liquid chromatography.