The rapid and reliable detection of SARS-CoV-2 seroconversion in humans is crucial for suitable infection control. In this sense, many studies have focused on increasing the sensibility, lowering the detection limits and minimizing false negative/positive results. Thus, biosensors based on nanoarchitectures of conducting polymers (CPs) are promising alternatives to more traditional materials, since they can hold improved surface area, higher electrical conductivity and electrochemical activity. In this work, we reported the analytical comparison of two different CPs morphologies for the development of an impedimetric biosensor to monitor SARS-CoV-2 seroconversion in humans. Biosensors based on polypyrrole (PPy), synthesized in both globular and nanotubular (NTs) morphology, and gold nanoparticles (AuNPs) are reported, using a self-assembly monolayer of 3-mercaptopropionic acid and covalently linked SARS-CoV-2 Nucleocapsid protein. Firstly, the novel hybrid materials were characterized by electron microscopy and electrochemical measurements, and the biosensor step-by-step construction was characterized by electrochemical and spectroscopic techniques. As a proof of concept, the biosensor was used for the impedimetric detection of anti-SARS-CoV-2 Nucleocapsid protein monoclonal antibodies. The results showed a linear response for different antibody concentrations, good sensibility and possibility to quantify 7.442 and 0.4 ng mL -1 of monoclonal antibody for PPy in the globular and nanotubular morphology, respectively. The PPy-NTs biosensor was able to discriminate serum obtained from COVID-19 positive vs negative clinical samples and is a promising tool for COVID-19 immunodiagnostic, which can contribute to further studies concerning rapid, efficient, and reliable detections.

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Poly­(3,4-ethylenedioxythiophene) nanotubes (PEDOT-NTs) were electrochemically synthesized onto a stainless steel mesh electrode followed by one-pot electrodeposition of gold nanoparticles (AuNPs) at the nanotubular surface. The hybrid nanomaterial has shown remarkable electrochemical properties with the diminishment of the charge transfer resistance besides the possibility of further electrode modification by the thiol bonding at the AuNPs. The modified electrodes were deeply characterized by electrochemical techniques, in special by electrochemical impedance spectroscopy, which provides valuable information about the interfacial processes. The morphology of the nanomaterial was characterized by scanning electron microscopy and transmission electron microscopy images. The biosensing properties were evaluated through the avidin/biotin pair. The methodology of construction of the biosensor was further adapted to explore a cancer biomarker detection, the folate binding protein (FBP), which presented high sensitivity with a limit of detection of 4.5 pmol L–1, one of the lowest found in literature. Also, the hybrid material was used in the development of supercapacitors, the inclusion of AuNPs provided a remarkable durability of the PEDOT-NTs modified electrodes presenting long cycling stability (over 3000 cycles) and high energy density, compared with bare PEDOT nanotubes modified electrodes.

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In this study, polypyrrole nanotubes (PPy-NT) and gold nanoparticles (AuNPs) were electrochemically synthesized to form a hybrid material and used as an electroactive layer for the attachment of proteins for the construction of a high-performance biosensor. Besides the enhancement of intrinsic conductivity of the PPy-NT, the AuNPs act as an anchor group for the formation of self-assembly monolayers (SAMs) from the gold–sulfur covalent interaction between gold and Mercaptopropionic acid (MPA). This material was used to evaluate the viability and performance of the platform developed for biosensing, and three different biological approaches were tested: first, the Avidin-HRP/Biotin couple and characterizations were made by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), wherein we detected Biotin in a linear range of 100–900 fmol L−1. The studies continued with folate group biomolecules, using the folate receptor α (FR-α) as a bioreceptor. Tests with anti-FR antibody detection were performed, and the results obtained indicate a linear range of detection from 0.001 to 6.70 pmol L−1. The same FR-α receptor was used for Folic Acid detection, and the results showed a limit of detection of 0.030 nmol L−1 and a limit of quantification of 90 pmol L−1. The results indicate that the proposed biosensor is sensitive and capable of operating in a range of clinical interests.