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 10(2) Ω M(−1) (r(2) = 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-bDNAp(1) 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.