Biosensors for dual detection of SARS-CoV-2 combining SERS and electrochemical impedance

The global emergency situation due to SARS-CoV-2 demands the development of fast, reliable and low-cost methods for diagnosing the virus. The diagnostic gold-standard is the RT-PCR (Reverse-Transcription Polymerase Chain Reaction), which requires time, specialized operator and expensive equipment. In contrast, methods based on serological immunoassays may be relatively faster and less expensive, but are subject to high variability in the patients' immune response. In this project, we propose a detection assay encompassing an immunomagnetic separation and preconcentration followed by dual detection via SERS (Surface-Enhanced Raman Scattering) and electrochemical impedance in a sandwich configuration. For immunomagnetic separation, magnetic core and gold shell nanoparticles (Au@MNP) will be produced, properly functionalized with a SERS marker (4-mercaptobenzoic acid, 4-MBA) and monoclonal anti-SARS-CoV-2 Spike (S) protein (capture antibody, Ab1) forming Au@MNPAb1 conjugates. These conjugates will be incubated with samples containing the S glycoprotein SARS-CoV-2 (antigen, Ag), thus forming Au@MNPAb1Ag conjugates which after magnetic extraction, will be sequentially incubated on a gold sensing surface functionalized with polyclonal anti-S glycoprotein SARS-CoV-2 antibodies (detection antibody, Ab2) for dual electrochemical (by electrochemical impedance spectroscopy) and SERS detection. The sandwich approach using the Au@MNPAb1 conjugates must guarantee specificity, facilitate separation, purification and preconcentration, as well as act as a signal amplifying agent, both for electrochemical impedance measurements and for SERS. In the context of the thematic project 2018/22214-6, we expected to obtain collaborations with specialized groups so that, after sensor manufacturing and optimization through the S proteins, tests can be carried out on real samples infected with SARS-CoV-2.