Biosensing strategies for the detection of SARS-CoV-2 nucleic acids

The COVID-19 pandemic had devastating effects throughout the world, producing a severe crisis in the health systems and in the economy of a long list of countries, even developed ones. Therefore, highly sensitive and selective analytical bioplatforms that allow the descentralized and fast detection of the severe acute respiratory síndrome coronavirus 2 (SARS-CoV-2), are extremely necessary. Since 2020, several reviews have been published, most of them focused on the different strategies to detect the SARS-CoV-2, either from RNA, viral proteins or host antibodies produced due to the presence of the virus. In this review, the most relevant biosensors for the detection of SARS-CoV-2 RNA are particularly addressed, with special emphasis on the discussion of the biorecognition layers and the different schemes for transducing the hybridization event. Graphical abstract

Impedimetric and amperometric genosensors for the highly sensitive quantification of SARS-CoV-2 nucleic acid using an avidin-functionalized multi-walled carbon nanotubes biocapture platform.

We report two novel genosensors for the quantification of SARS-CoV-2 nucleic acid using glassy carbon electrodes modified with a biocapture nanoplatform made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with avidin (Av) as a support of the biotinylated-DNA probes. One of the genosensors was based on impedimetric transduction offering a non-labelled and non-amplified detection of SARS-CoV-2 nucleic acid through the increment of [Fe(CN)6]3-/4- charge transfer resistance. This biosensor presented an excellent analytical performance, with a linear range of 1.0 × 10-18 M - 1.0 × 10-11 M, a sensitivity of (5.8 ± 0.6) x 102 Ω M-1 (r2 = 0.994), detection and quantification limits of 0.33 aM and 1.0 aM, respectively; and reproducibilities of 5.4% for 1.0 × 10-15 M target using the same MWCNTs-Av-bDNAp nanoplatform, and 6.9% for 1.0 × 10-15 M target using 3 different nanoplatforms. The other genosensor was based on a sandwich hybridization scheme and amperometric transduction using the streptavidin(Strep)-biotinylated horseradish peroxidase (bHRP)/hydrogen peroxide/hydroquinone (HQ) system. This genosensor allowed an extremely sensitive quantification of the SARS-CoV-2 nucleic acid, with a linear range of 1.0 × 10-20 M - 1.0 × 10-17 M, detection limit at zM level, and a reproducibility of 11% for genosensors prepared with the same MWCNTs-Av-bDNAp1 nanoplatform. As a proof-of-concept, and considering the extremely high sensitivity, the genosensor was challenged with highly diluted samples obtained from SARS-CoV-2 RNA PCR amplification.