Conventional PCR Assisted Single-Component Assembly of Spherical Nucleic Acids for Simple Colorimetric Detection of SARS-CoV-2

Karami, Abbas; Hasani, Masoumeh; Jalilian, Farid Azizi; Ezati, Razieh

Continuous identification of suspected infectious cases is crucial to control the recent pandemic caused by the novel human coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). Real-time polymerase chain reaction (real-time PCR) technology cannot be implemented easily and in large scale in some communities due to lack of resources and infrastructures. Here, we report a simple colorimetric strategy derived from linker-based single-component assembly of gold nanoparticle core-spherical nucleic acids (AuNP-coreSNAs) for visual detection of PCR products of SARS-CoV-2 ribonucleic acid (RNA) template. A palindromic linker is designed based on E gene of SARS-CoV-2 to program the identical colloidal SNAs into large assemblies along with a distinct red-to-purple color change. The linker acts as a probe of SARS-CoV-2 RNA in conventional PCR reaction. In the presence of the correct template, the palindromic linker, which is complementary to a short region within the amplicon, is cleaved by 5’-exonuclease activity of deoxyribonucleic acid (DNA) polymerase. Disintegrating the palindromic linker during the amplification process inhibits the post single-component assembly formation of SNAs. So, positive and negative viral samples produce simply red and purple colors in the post PCR colorimetric test, respectively. Evaluation of the samples obtained from cases with laboratory-confirmed SARS-CoV-2 infection revealed that our assay can rival with Real-time PCR method in sensitivity.