R than that of SWCNTs [114]. Considering the fact that GR-modified electrodes exhibit a wide
R than that of SWCNTs [114]. Considering that GR-modified electrodes exhibit a wide electrochemical possible window, the determination of molecules in a wide prospective variety is feasible. For this reason, GR would be the most normally employed material for electrodes in biosensors [115]. GR has two principal derivatives with various degrees of oxidation: graphene oxide (GO) and lowered graphene oxide (rGO). The improved solubility of GO in an aqueous option is mainly as a result of its functional groups such as epoxides, hydroxyls, and carboxylic acids. These surface functional groups can interact using the functional groups of other biomolecules to be attached to their surface, supplying quite a few reaction internet sites [116]. Nonetheless, the presence of oxygen-rich functional groups in GO causes a reduce in electrical conductivity. Within this regard, GO is decreased with the desired modification for sensor applications. Just after reduction, most of the functional groups in GO are removed, and -conjugation-rich graphene is formed, which is called rGO. Therefore, the conductivity of graphene is restored through -conjugation, while its solubility in aqueous solutions or polar solvents decreases. Figure 4 depicts the oxidation and reduction actions to synthesize rGO from graphite.Figure 4. Oxidation and reduction methods to obtain decreased graphene oxide (rGO) from graphite. Reprinted with permission from ref. [117].In 2017, Settu and coworkers created an aptamer biosensor to detect Sunset Yellow FCF Description engrailed-2 (EN2, a biomarker for prostate cancer) according to carboxylated SPCE. The reactive sur-Nanomaterials 2021, 11,11 offace area was enhanced with all the incorporation of GR into a carbon paste electrode. This improved the electrical conductivity, resulting inside the improvement of a high-sensitivity biosensor technique. The linear DBCO-NHS ester web detection variety was 3585 nM, and also the LOD was 38.five nM. However, the calculated LOD value was not sufficient for the clinical diagnosis of EN2 protein. For that reason, additional investigation on signal enhancement is required to improve the LOD [118]. 1 year later, Baluta and coworkers prepared an electrochemical biosensor to sense epinephrine (EP) by utilizing graphene quantum dots (GQDs) and glassy carbon electrodes (GC) modified with laccase. Catecholamine was oxidized within the presence on the laccase, and an electrochemical signal was obtained. The linear detection range was 1 10-6 20 10-6 M, as well as the LOD was 83 nM, to detect EP in labeled pharmacological samples [119]. The following year, Karimi and coworkers created a molecularly imprinted polyaniline-based sensor with rGO to identify human cardiac troponin T (cTnT). MIP was obtained via electropolymerization around the rGO-modified SPCE inside the presence of cTnT and carboxylated aniline monomers. Then, cTnT was removed by oxalic acid remedy. The linear detection range with the developed biosensor was 0.02.09 ng mL-1 , and also the LOD was 0.008 ng mL-1 . This study suggests that the created biosensor method and HPLC have a superb correlation [120]. In 2020, Sharma and coworkers (2020) developed a label-free aptasensor depending on rGO modified with polyethylenimine (PEI) thin films for detection of cardiac myoglobin (cMbi, cardiac biomarker). PEI, a cationic polymer, was used for the reduction of graphene oxide (GO). Within this way, a constructive charge was formed around the rGO surface. The negatively charged single-stranded DNA aptamers were straight immobilized towards the sensor surface by electrostatic interaction devoid of any binding agent. The linear detection range of the develop.
