Towards SARS-CoV-2 detection at six orders of magnitude lower than RT-PCR via nanoplasmonic probes and MIPs

Managing pandemics caused by rapidly spreading pathogens, such as the one caused by the SARS-CoV-2 virus between 2020 and 2022, is one of the challenges that the international community needs to prepare for in the future due to the impact on both the economy and the different national health systems. Point-of-care devices with ultra-high sensitivity and specificity for local monitoring, such as Wastewater-based epidemiology (WBE), have been developed and presented to better control the spread of the pandemic emergency. In this work, the detection of SARS-CoV-2 virus in nasopharyngeal swab samples has been carried out by exploiting pollen-based nanoplasmonic chips functionalized with Molecularly Imprinted Polymers (MIPs) specific for the S1 spike protein of SARS-CoV-2, as a proof-of-concept. The nanoplasmonic phenomena are achieved via natural pollen-based nanostructures covered by a gold nanofilm. The MIP-based nanoplasmonic chip is small-size, low-cost, ultra-sensitive, and can be monitored via a simple and portable setup. The experimental results indicated that the developed sensitive system is able to measure the SARS-CoV-2 S1 spike protein with a detection limit approximately six orders of magnitude lower than the one achieved via the same MIP deposited on flat surface plasmon resonance (SPR) platforms. Therefore, tests on highly diluted (six orders of magnitude) nasopharyngeal swab samples have been performed with results in agreement with the gold standard test, a Reverse Transcription Polymerase Chain Reaction (RT-PCR) assay.