The COVID-19 pandemic brought the global need to develop new biosensors for practical use, with quick response, sensitivity, and low cost, aiming point-of-care diagnosis and mass monitoring concerning the contamination of a population. In this sense, graphene field effect transistors (GFETs) are among the most promising biodevices due to their sensitivity and rapidness of response. However, the low selectivity inherent to the response mechanism of GFETs and the use of a non-polarizable

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... electrode of the Ag/AgClsat type in its configuration limit its application. In this sense, this Doctorate Thesis presents the development and application of a new type of biosensor based on monolayer graphene, with hybrid detection, where the device uses electrical and electrochemical principles, called Graphene Vertical Electrical-Electrochemical Device (EEVD). EEVD was designed so that an electrode formed by the heterojunction of a graphene layer/adsorbed redox probe is exposed to the electrolyte and, as a result, small variations caused by the presence of analytes at the electrode/electrolyte interface change the charge density near the graphene K point of first Brillouin zone. This perturbation alters the Dirac point and causes energy dispersion, resulting in different values of capacitance and potential of the interface, which are strongly correlated to the presence of the analyte. Furthermore, it was observed that faradaic processes can occur in the orthonormal plane of graphene in the presence of a redox probe coupled by van der Waals interactions, intensifying the interface perturbation by the presence of the analyte in the electrolyte, making EEVD more sensitive when compared to GFET. As a proof of concept, a EEVD based on the graphene/ferrocene heterojunction was used for single-stranded DNA detection, obtaining a limit of detection (LOD) of zeptomolar magnitude order (10 -21 mol L -1 ). Because it has a total negative charge, DNA changes the capacitance of the interface formed by the heterojunction, and varies its open circuit potential (OCP), which in turn responds linearly to alterations of DNA concentrations. Therefore, EEVD was applied as an immunosensor for the diagnosis of COVID-19. For this, ferrocene was replaced by the neutral red redox probe modified with Spike protein receptor binding domain (RBD) of SARS-CoV-2. In this configuration, the biosensor requires 40 μL of serum sample from a patient infected with COVID-19, and it is possible to detect IgG antibodies produced in response to COVID-19 infection with an LOD of 1.0 pg mL -1 . Finally, an EEVD-type biosensor was developed for antigen detection (SARS-CoV-2 virus) in saliva samples, with a LOD of 2.86 fmol L -1 , indicating the suitability of the biosensor for the diagnosis of COVID-19 in early stage. Both the immunosensor and the antigen biosensor for the diagnosis of COVID-19 were validated in real samples and using validation parameters from ANVISA and ABRAMED.