Graphene and its derivatives have been widely used for the electrochemical detection of dopamine (DA) neurotransmitter, thanks to its high surface area and excellent conductivity. Modified graphene and graphene-based nanocomposites have shown improved catalytic activity towards DA detection. Various modification approaches have been taken, including heteroatom doping and association with other nanomaterials. This review summarizes and highlights the recent advances in graphene-based electrodes for the electrochemical detection of DA. It also aims to provide an overview of the advantages of using polymer as a linker platform to form graphene-based nanocomposites applied to electrochemical DA sensors.

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Electrochemical sensor for the individual and the simultaneous detection of dopamine (DA), ascorbic acid (AA) and uric acid (UA) based on redox conjugated "poly(paraphenylene)" (Fc-ac-PPP) bearing ferrocene and carboxylic acid in lateral position has been developed. The electrochemical characterization of the sensor has been studied with cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CA). We highlighted that the catalytic activity of the Fc-ac-PPP polymer provided by it's redox electrochemical properties and chemical structure allows to the electrochemical detection of DA, AA and UA. We demonstrated that the sensor provides high sensitivity and selective signal in the coexistence of DA, AA and UA within short time. Low detection limits and wide linear ranges of detection have been demonstrated respectively for DA 3×10 -10 M (1nM-10µM), AA 1.6×10 -8 M (0.1 µM -1mM), and UA 1×10 -8 M (0.1µM-1mM). In addition, the sensor has been successfully applied to determine DA in urine and human serum samples even in the presence of high concentrations of AA and UA. This sensor could be a powerful device for the detection of other electroactive compounds thanks to it's high catalytic properties and chemical structure.

Association of graphene with conjugated organic macromolecules presents an interest in various applications. Here, we study the chemical and electrical properties of nanomaterials which combine the features of chemical reduced graphene oxide (CRGO) and its modification with tetrabutyloxyphenylporphyrins bearing a mono-or tetra-carboxylic functions. The hybrid nanomaterials are characterized through different techniques including UV-visible, FT-IR, Raman spectroscopy, MEB and SEM. Their electrochemical properties are studied by cyclic voltammetry (CV) with inner sphere and outer sphere redox markers as well as electrochemical impedance spectroscopy (EIS). The overall results support the formation of strong interactions between porphyrins and CRGO. Furthermore, we highlight the relationship of structural and electronic properties of porphyrins on the resulted composite. Thus, we demonstrate that modified porphyrins with alkoxy and carboxyl groups improve the dispersion of CRGO and have positive effects on their electronic properties in particular the electron transfer ability. These nanocomposites open new opportunities for their application in biosensors devices and the detection of DNA of M. Tuberculosis was demonstrated with LOD at attomolar range and an ability to discrimination of M. tuberculosis strand from mutated in PCR sample.

In this study, an efficient and simple designed nanohybrid created for individual and simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). This nanohybrid is a combination of chemical reduced graphene oxide (CRGO) and redox poly(para-phenylene) (Fc-ac-PP) modified in a lateral position with ferrrocenyl group CRGO/Fc-ac-PPP. The CRGO/Fc-ac-PPP nanohybrid demonstrated a synergistic effect resulting in a large conductivity, surface area and catalytic properties provided by the redox attached ferrocene. Moreover, this nanocomposite is able to detect individually as well as simultaneously AA, DA and UA in a co-existence system with defined and separated redox peaks oxidation. The linear response ranges for AA, DA and UA, when detected simultaneously, are 0.1–10000 μM, 0.0001–1000 μM and 0.1–10000 μM, respectively, and the detection limits (S/N = 3) are 0.046 μM, 0.2 nM and 0.013 μM, respectively. The proposed sensor shown satisfactory results when applied to real spiked urine samples for measuring the abnormal high or lowconcentration of AA, DA and UA in vivo.

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