Researchers at the Agricultural University of Athens, Greece, have developed an innovative portable biosensor for the rapid, ultra-sensitive and scaled-up detection of the SARS-CoV-2 virus surface S1 protein. This new test potentially allows the virus to be detected immediately after an individual becomes infected, while even asymptomatic patients could be identified in the early stages of the virus spread.
The ability to reliably predict the spread of the novel and highly contagious SARS-CoV-2 coronavirus created an urgent need for diagnostic tools able not only to reliably identify infected individuals but also determine the stage of viral replication and spread. A priority goal of the worldwide management of the COVID-19 pandemic is the reduction in the time required to confirm positive cases between infection and symptom appearance, in particular during the very early infection period (1–3 days) and identifying asymptomatic patients.
Currently available serological assays for SARS-CoV-2 screen host antibodies raised against the virus, therefore they are not suitable for monitoring infection at an early stage (up to the first three days). An attractive alternative option is the screening of the SARS-CoV-2 S1 spike protein antigen, which is implicated in the initial stages of viral entry, corresponding to the presence of the whole virus.
The novel biosensor is based on membrane-engineered Vero mammalian cells bearing the human chimeric spike S1 antibody. This was achieved by using a generic methodology known as Molecular Identification through Membrane Engineering which comprises of electroinserting tens of thousands of antibody molecules on the cell surface, thus rendering the cell a selective responder against antigens binding to the inserted antibodies. It has been proven in numerous previous applications that the attachment of the target antigen to its respective antibody causes a change in the cell membrane structure, which is measurable as a change in the cell membrane potential. Therefore, membrane-engineered cells can be used as biorecognition elements in appropriate bioelectric sensors. For the detection of the SARS-CoV-2 virus surface S1 protein, the biosensor set-up was configured according to the principles of the established Bioelectric Recognition Assay (BERA) as a portable read-out device operated via smartphone/tablet. The response of Vero/anti-S1 cells immediately after the addition of the sample was recorded as a time-series of potentiometric signal at a sampling rate of 2 Hz. The measurements were uploaded via a tablet/Bluetooth communication to a cloud server. The system provided results in an ultra-rapid manner (3 min), with a detection limit of 1 fg/mL and a semi-linear range of response between 10 fg and 1 μg/mL. No cross-reactivity was observed against the SARS-CoV-2 nucleocapsid protein. Beyond speed, the high sensitivity of the novel biosensor could allow non-invasive virus detection in saliva samples.
The novel biosensor, having been tested at the proof-of-concept, offers capabilities for high throughput and low-cost mass screening of the coronavirus antigens. The next step is the clinical validation of the assay in actual patient samples as well as broadening the scope of application to detect antigenic S proteins of other coronaviruses.
Reference: Mavrikou, S., Moschopoulou, G., Tsekouras, V., & Kintzios, S. (2020). Development of a Portable, Ultra-Rapid and Ultra-Sensitive Cell-Based Biosensor for the Direct Detection of the SARS-CoV-2 S1 Spike Protein Antigen. Sensors, 20(11), 3121. doi:10.3390/s20113121
Professor Spyridon Kintzios is Rector of the Agricultural University of Athens/EU CONEXUS European University.