Food safety is a major concern for human health and wellbeing all over the world. A novel and sensitive biosensor based on reduced graphene oxide (rGO) and the enzyme acetylcholinesterase (AChE) was developed and applied for the detection of carbaryl in food samples. The glassy carbon/rGO/AChE biosensor was characterized morphologically and electrochemically using scanning electron microscopy and cyclic voltammetry/electrochemical impedance spectroscopy, respectively. Optimum differential pulse voltammetry conditions led to a nanomolar detection limit, and determination of carbaryl in tomato was achieved.

This work presents the development of a sensor based on reduced graphene oxide (rGO) modified with silver nanoparticles (AgNPs) for the oxidation of estriol hormone. The morphology and electrochemical behavior of the rGO-AgNPs composite was characterized by scanning electron microscopy and cyclic voltammetry, demonstrating that the AgNPs were incorporated into rGO. The transfer of an electron from the estriol molecule for the working electrode at +0.45 V, and the consequent loss of an H + ion for the buffer solution was confirmed combining electrochemical experiments and molecular modelling techniques. The glassy carbon (GC) electrode modified with the rGO/AgNPs composite was optimized for the determination of estriol using differential pulse voltammetry (DPV), achieving detection limit of 21.0 nmol L − 1 for estriol hormone. Reproducibility and repeatability values of 1.5% and 1.3%, respectively, were obtained compared to the conventional procedure. The proposed GC/rGO-AgNPs electrochemical device was successfully applied to the determination of estriol in tap water and synthetic urine samples.

Due to the SARS-CoV-2 pandemic, there has been an increase in the search for affordable healthcare devices for mass testing and rapid diagnosis. In this context, this work described a new methodology for SARS-CoV-2 detection based on an impedimetric immunosensor developed using the advantageous immobilization of antibodies in the reduced graphene oxide (rGO). The rGO was obtained by chemical synthesis from the commercial graphene oxide (GO), and the materials were morphologically, electrochemically and visually characterized. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were used to evaluate the fabrication steps of the immunosensor. The electrochemical immunoassay was considered for SARS-CoV-2 spike protein RBD detection using a impedimetric immunosensor and redox couple ([(Fe(CN)6)]3−/4−) as a probe. The immunosensor was effectively developed and applied in the detection of SARS-CoV-2 spike protein RBD in saliva samples.

This work presents, for the first time, the oxidation mechanism of levofloxacin combining electrochemical experiments and molecular modelling techniques. Levofloxacin is one of the most widely used antibiotics in the world. The detection of this antibiotic is important, because it cannot be fully assimilated by the human organism, therefore levofloxacin is considerate a hazardous pollutant for environment. Sensors based on reduced graphene oxide (rGO) modified with antimony and copper nanoparticles (NPs) were synthesized, characterized and evaluated for the electrochemical detection of the levofloxacin. The morphological and electrochemical characterization of the composites confirmed that the rGO was modified with the metallic nanoparticles. Molecular modelling studies were performed applying Density Functional Theory (DFT) approach, which indicated that the mechanism of levofloxacin oxidation is given by the loss of two electrons: one from N14 atom and other from C13 atom of the levofloxacin molecule. The glassy carbon electrode (GCE) modified with the SbNPs/rGO and CuNPs/rGO composites were evaluated for the determination of levofloxacin using differential pulse voltammetry (DPV) and achieved detection limit of 4.1×10−8 mol L−1 and 1.7×10−8 mol L−1, respectively, presenting as alternative composites to be used in the analysis of antibiotics.

Bioelectrodes were developed based on a simple deposition of graphene oxide (GO) or reduced graphed oxide (rGO) and laccase (Lac) on a glassy carbon (GC) electrode surface. The morphology and electrochemical behavior of the biosensors were characterized by scanning electron microscopy and cyclic voltammetry. These results demonstrated that only rGO was successfully applied for the immobilization of the laccase enzyme, improving the analytical signal for the determination of dopamine. The GC/rGO/Lac biosensor was applied to the detection of dopamine in synthetic urine and plasmatic serum samples, achieving a detection limit of 91.0 nmol L −1 .

A simple, cheap, and less aggressive immobilization procedure for biomolecules using reduced graphene oxide (rGO) was employed to prepare an impedimetric immunosensor for detection of staphylococcal enterotoxin A (SEA) from Staphylococcus aureus in milk samples. The scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) were used to monitor the single steps of the electrode assembly process. The glassy carbon (GC)/rGO platform detected the antigen-antibody binding procedures of SEA with concentrations of 0.5 to 3.5 mg L−1 via impedance changes in a low frequency range. The impedimetric immunosensor was successfully applied for the determination of SEA in milk samples.

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A nanocomposite based on reduced graphene oxide (rGO) and gold nanoparticles (AuNPs) was synthesized by the microwave-assisted hydrothermal method and applied in the determination of sulfamethazine (SMZ) in swine effluent using a glassy carbon (GC) electrode. The rGO-AuNPs nanocomposite was characterized morphologically, electrochemically and spectrochemically, showing that rGO was modified with the AuNPs. The GC/rGO-AuNPs electrode was optimized for the determination of SMZ, achieving detection limits of 0.1 μmol L−1. The proposed sensor was successfully applied to the determination of SMZ in synthetic swine effluent samples.