A SARS-Cov-2 sensor based on upconversion nanoparticles and graphene oxide

Abstract

Since the beginning of the COVID-19 pandemic, there has been an increased need for the development of novel diagnostic solutions that can accurately and rapidly detect SARS-CoV-2 infection. In this work, we demonstrate the targeting of viral oligonucleotide markers within minutes without the requirement of a polymerase chain reaction (PCR) amplification step via the use of oligonucleotide-coated upconversion nanoparticles (UCNPs) and graphene oxide (GO).

Scheme 1. Detection of an oligonucleotide target associated with the RdRp/Hel gene of SARS-CoV-2. Oligonucleotide-coated UCNPs designed to detect part of the SARS-CoV-2 gene are incubated with the target of interest. Upon addition of GO and irradiation with a laser at 980 nm, the fluorescence signature originating from the UCNPs is monitored. The absence of a fluorescence signal would indicate that the target is not present and fluorescence quenching has taken place following adsorption of the nanoparticles onto the GO surface.

Fig. 1. Representative transmission electron microscopy images of core (A) and core–shell UCNPs (B) and their corresponding size distribution histograms (C and D). Scale bar is 100 nm.

Fig. 2. (A) Representative fluorescence emission spectrum from oligonucleotide coated UCNPs (0.5 mg mL⁻¹) in the presence of increasing concentrations of GO. (B) Correlated fluorescence emission spectrum from oligonucleotide coated UCNPs (0.5 mg mL⁻¹) showing the decreasing fluorescence emission of the λ_max of the two typical peaks of UCNPs (655 nm, red points; 540 nm, cyan points) in the presence of increasing concentration of GO.

Fig. 3. (A) Representative fluorescence spectrum of oligonucleotide coated UNCPs (0.5 mg mL⁻¹) after incubation with increasing concentrations of cDNA targets in the presence of GO (B) graph of the maximum UCNP fluorescence intensity measured at 540 nm (cyan points) and 655 nm (red points) in the presence of GO as a function of cDNA concentration.

Fig. 4. Fluorescence spectrum of oligonucleotide coated UCNPs (0.5 mg mL⁻¹) in the absence of ncDNA and GO (unquenched) and in the presence of increasing concentrations of a ncDNA sequence and GO (0.6 mg mL⁻¹). For comparison the fluorescence spectrum of oligonucleotide coated UCNPs in the absence of GO is shown.