An Innovative PCR-Free Nanotechnology for SARS-CoV-2 Sensing

The molecular analysis of Nucleic Acids (NA), DNA and RNA, has become nowadays crucial in many medical fields for early and accurate diagnosis, personalized therapy and preventive screening. It is particularly relevant in the field of the infectious diseases that can catastrophically affect the health of population, as it is the case of the current pandemic of SARS-CoV-2 virus that – up to now – infected up to 434 million of people causing 6 million of deaths worldwide.<br/>In this scenario, the conventional approach for the molecular analysis of SARS-CoV-2 is based on the PCR (Polymerase Chain Reaction) reaction that, although standardized and consolidated, is quite complex and includes multiple laboratory procedures and high cost that limit, <i>de facto</i>, its massive use. These limitations make the PCR-based analysis inconsistent with the idea of an efficient patient management, in terms of fast diagnosis and prompt answer to the treatment, and viral outbreaks containment.<br/>The PCR-free approach, that allows a fast, ultrasensitive, low cost and easy to use identification and quantification of the pathogen genome without its amplification, overcomes this issue introducing innovative methodologies suitable for the decentralised and massive infections diagnoses and prevention.<br/>In this contribution we present an innovative PCR- and label-free technology for the SARS-CoV-2 genome photoluminescent (PL) detection based on the silicon NanoWires (Si-NWs), one of the most appealing silicon nanomaterials employed in nanodevices for biosensing applications. The strategy involves the surface capture of the whole viral genome via a cooperative hybridization with two complementary capture probes (single stranded DNA) that are grafted on the Si-NWs surface. The hybridization is, then, optically transduced through the quenching effect of the PL signal that is intrinsically produced by the Si-NWs, due to the quantum confinement at room temperature. The occurrence of a non-radiative phenomena, introduced by the SARS-CoV-2 genome hybridization on the Si-NWs surface, determines the quenching of the PL signal and the PCR- and label-free identification and quantification of the viral RNA, with a Limit of Detection (LoD) of 4 RNA copies, below the LoD of the PCR gold standard method. Moreover, the proposed technology is suitable for Molecular “Point-of-Care” (M-PoC) applications, matching the vision of future home-made infective diagnostic microchips integrated into smart mobile devices (i.e smartphones or smart watches).