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.

The development of electroanalytical sensors for heavy metals detection in complex matrices holds great interest. Herein, a sensor based on a reduced graphene oxide (rGO) modified with antimony nanoparticles (Sb) was developed for the electrochemical detection of divalent cadmium ions (Cd²⁺) and lead ions (Pb²⁺). The simultaneous determination of both metals covered a range of 0.1 to 3.0 µmol L⁻¹, with limits of detection (LOD) of 70.03 and 45.50 nmol L⁻¹ for Cd²⁺ and Pb²⁺, respectively. For the individual detection, LOD of 20.50 nmol L⁻¹ (Cd²⁺) and 2.01 nmol L⁻¹ (Pb²⁺) were found. The analytical performance of this new sensor in detecting both metals in chamomile tea samples was satisfactorily evaluated.