The dramatic global health emergency due to the SARS-CoV-2 pandemic requires new diagnostic devices capable of identifying the presence of virus particles in patient biological samples. In this direction, the development of an innovative low-cost test, which provides the result within a few minutes, which is reproducible and which can reveal the direct presence of even a few viral particles, would be of fundamental importance for the monitoring and containment of the pandemic. CoBRa-Sens is a point-of-care test (PoCT) based on an innovative, low-cost and ultra-rapid fluorescence transfer biosensor, which identifies the direct presence of the virus with high sensitivity in a few microliters of saliva. The device to be built consists of integrated system collection optics of spectrally-resolved fluorescence, for coupling the light to a digital camera connected to a smartphone.
The biological moiety of CoBRa-Sens is a multi-domain protein (PMD) containing at its ends both the viral Sp1RBD (Spike domain for the interaction with human ACE2) and idACE2 (the minimal domain of ACE2). The strong interaction between them leads to a "U" shape of the PMD with an absence of fluorescence photons (dark state), since it brings a quencher molecule closer to a fluorophore, both conjugated to PMD. The surface Spike receptors on a few free viral particles in the sample, on the other hand, interrupt the Sp1RBD-idACE2 interaction, shifting the equilibrium towards a linear "I" shape of the PMD, effectively moving the quencher away from the fluorophore and allowing the emission of photons (bright state). The CoBRa-Sens could allow a very high signal/noise ratio, placing our approach at the frontier with respect to the state of the art of research, with low-cost technology and making possible its use without the need for advanced skills.