Electronic bio-sensor for SARS-CoV-2 infectivity detection

Robert Strassl, Head of the Division of Clinical Virology at the Department of Laboratory Medicine of the Medical University of Vienna, and his interdisciplinary team (Anna Nele Herdina, MedUni Wien; Patrik Aspermair, AIT; Miriam Klausberger, BOKU) have received funding from the Austrian Science Fund (FWF) to develop a new electronic biosensor for the discrimination of SARS-CoV-2 variants and infectivity. The ongoing COVID-19 pandemic is claiming further deaths daily and poses unprecedented challenges for the health systems of many countries. The rapid recognition and containment of new coronavirus SARS-CoV-2 variants of concern play major roles in curbing the pandemic. An important factor in managing treatment and isolation of COVID-19 patients and contacts is their infectivity status. Whether a patient is (still) contagious, can currently only be answered by performing a time- consuming viral culture in special biosafety laboratories. The aim of this multidisciplinary project is to develop a novel electronic biosensor for the rapid detection of SARS-CoV-2. The new biosensor is anticipated to allow for an immediate discrimination of known variants of concern and could also serve as sentinel system for recognizing new variants. The underlying technology is further anticipated to detect virus, which is able to reproduce, and should therefore allow to infer a patients infectivity status to determine a patients infectivity. This novel method of SARS-CoV-2 detection, as well as variant and infectivity discrimination, could contribute to curb the pandemic and help to conserve resources for patient isolation in overtaxed health systems. Additionally, the novel technique can later be adapted to detect other viruses and their infectivity.

Important factors in managing treatment and isolation of patients with COVID-19 and other infectious diseases are rapid diagnosis and knowledge about a patient's infectivity status. While viral culture in special biosafety laboratories is the gold-standard for infectivity determination, it is time-consuming and not used for routine diagnostics. To address these needs, we have developed and tested graphene field-effect-transistor (gFET) based biosensor assays for SARS-CoV-2 diagnosis: one RNA detection assay to test for viral presence and the other for nucleocapsid (N-) protein detection as a proxy for infectiousness of the patient. A biosensor is a device that transduces a biological signal, the binding of a biological receptor to a specific analyte, into a physical output signal. By integrating and combining an optical, surface plasmon resonance (SPR), and an electronic, gFET, biosensor systems, our project sets the foundation for a new generation of biosensors with enhanced sensitivity and specificity. In the initial optimization phase, we use a combination system where both SPR and gFET provide simultaneous, complementary readouts from the same sensor surface. This provided a better understanding of biomolecular interactions and enabled us to correlate the results into gFET based sensing in clinical settings. In a first step, single stranded DNA probes were used to capture SARS-CoV-2 E-gene RNA in clinical nasopharyngeal swab samples from (pseudonymized archived residual material). This RNA detection assay delivered results comparable to RT-PCR in sensitivity and specificity. For N-protein detection we used a specific antibody as a probe. The limit of detection (LOD) for N-protein of the gFET biosensor was of 0.9 pM, establishing a foundation for the development of a sensitive tool for monitoring active viral infection. In clinical samples, results of gFET based N-protein detection corresponded to the results of virus culture, and thus proved the biosensor's capability to serve as a proxy for infectivity. Additionally, we tested and implemented a standardized NaCl-calibration to improve reproducibility and device-to-device variation between experiments on graphene coated interdigitated electrode-chips (IDE). Experiments on SARS-CoV-2 variant detection by using ACE2 probes to capture custom produced trimeric spike ectodomain proteins (wildtype, Alpha, Beta, Gamma, Delta, Omicron BA1, Omicron BA2, Omicron BA5) showed promising results. However, due to the everchanging nature of viral mutations, further refinement is required. Interdisciplinary research in the areas of surface chemistry, biophysics, and virology enabled the development of an ultra-sensitive method for rapid detection of respiratory viruses in a clinical setting. Overall, these findings support the potential of the gFET biosensor as a point-of-care device for rapid diagnosis of SARS-CoV-2 infection and indirect assessment of infectiousness in patients, providing additional information for clinical and public health decision making.