The severe acute respiratory syndrome coronavirus type 2 (SARS-CoV2) is an enveloped positive-sense single stranded RNA virus that has been identified in the beginning of 2020 (1). It infects human host cells by docking via its spike protein (S) to the ACE2 surface receptor (2) and can cause mild to very severe and even deadly Covid-19 courses (3).
The very abundant Nucleocapsid or N-protein packages the viral RNA (4) and shares only little homology to other abundant members of the coronavirus family like NL63, 229E, HKU1 or OC43. This characteristic makes it a suitable target to discriminate between Covid-19 and other Coronavirus infections.
Unlabeled variants and several modifications of sdAbs like biotin, fluorophore or DBCO conjugation are available.
In FluoTag®-Q each fluorophore is coupled to exactly one FluoTag, which in turn binds to its target molecule in a monovalent fashion. The high binding affinity and a coupling efficiency of > 95% guarantees a highly linear relation between the number of target molecules and the intensity of fluorescence. This enables a direct count of the target molecule of interest. The fluorophore is located exceptionally close to the recognized epitope (< 1.5 nm), which is ideal for all microscopy techniques.