Optical Biosensing of SARS-CoV-2 RNA Based on Positively Charged Poly-l-Lysine Functionalized Gold Nanoparticles

The World Health Organization (WHO) announced corona virus disease 2019 (COVID-19) caused by severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), a serious pandemic in March 2020. The situation demands, development of rapid, convenient and easy to handle detection system for SARS-CoV-2. In this regard, the optical biosensing assay was developed using antisense oligonucleotide (ASO) conjugated Poly-l-Lysine functionalized gold nanoparticles (PLL-AuNPs) for detection of SARS-CoV-2 RNA. The negatively charged ASOs were conjugated with positively charged PLL-AuNPs by electrostatic interactions which were characterized by UV–Vis spectroscopy and Transmission Electron Microscopy (TEM). ASO-PLL-AuNPs conjugate was used to detect target SARS-CoV-2 RNA within 5–6 min from COVID-19 positive samples. In presence of target SARS-CoV-2 RNA, the DNA-RNA (ASO-RNA) hybrid structure was formed that released PLL-AuNPs which was aggregated in presence of sodium chloride (NaCl). This has rendered observable red shift in Surface Plasmon Resonance (SPR) with maximum absorbance at 660 nm and visual aggregation of PLL-AuNPs. Selectivity of ASO-PLL-AuNPs conjugate was evaluated in presence of Influenza A RNA with limit of detection 0.52 ng/µL. The obtained results were compared with qRT-PCR results for nasopharyngeal samples collected from COVID-19 positive patients and were found in good agreement with qRT-PCR results. This study reports selective and sensitive optical biosensing assay for detection of SARS-CoV-2 RNA using ASO-PLL-AuNPs conjugate without utilization of any sophisticated instruments.

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