Proof-of-concept for speedy development of rapid and simple at-home method for potential diagnosis of early COVID-19 mutant infections using nanogold and aptamer

Abstract

The positive single-stranded nature of COVID-19 mRNA led to the low proof-reading efficacy for its genome authentication. Thus mutant covid-19 strains have been rapidly evolving. Besides Alpha, Beta, Gamma, Delta, and Omicron variants, currently, subvariants of omicron are circulating, including BA.4, BA.5, and BA.2.12.1. Therefore, the speedy development of a rapid, simple, and easier diagnosis method to deal with new mutant covid viral infection is critically important. Many diagnosis methods have been developed for COVID-19 detection such as RT-PCR and antibodies detection. However, the former is time-consuming, laborious, and expensive, and the latter relies on the production of antibodies making it not suitable for the early diagnosis of viral infection. Many lateral-flow methods are available but might not be suitable for detecting the mutants, Here we proved the concept for the speedy development of a simple, rapid, and cost-effective early at-home diagnosis method for mutant Covid-19 infection by combining a new aptamer. The idea is to use the current lateral flow Covid-19 diagnosis system available in the market or to use one existing antibody for the Lateral Flow Nitrocellulose filter. To prove the concept, the DNA aptamer specific to spike proteins (S-proteins) was conjugated to gold nanoparticles and served as a detection probe. An antibody that is specific to spike proteins overexpressed on COVID viral particles was used as a second probe immobilized to the nitrocellulose membrane. The aptamer conjugated nanoparticles were incubated with spike proteins for half an hour and tested for their ability to bind to antibodies anchored on the nitrocellulose membrane. The gold nanoparticles were visualized on the nitrocellulose membrane due to interaction between the antigen (S-protein) with both the aptamer and the antibody. Thus, the detection of viral antigen can be obtained within 2 h, with a cost of less than $5 for the diagnosis reagent. In the future, as long as the mutant of the newly emerged viral surface protein is reported, a peptide or protein corresponding to the mutation can be produced by peptide synthesis or gene cloning within several days. An RNA or DNA aptamer can be generated quickly via SELEX. A gold-labeled aptamer specific to spike proteins (S-proteins) will serve as a detection probe. Any available lateral-flow diagnosis kits with an immobilized antibody that has been available on the market, or simply an antibody that binds COVID-19 virus might be used as a second probe immobilized on the nitrocellulose. The diagnosis method can be carried out by patients at home if a clinical trial verifies the feasibility and specificity of this method.

Keywords: Early-stage COVID-19 diagnosis; Lateral flow assay; Oligonucleotide aptamer; Spike protein.

Graphical abstract

Fig. 1

Illustration of the design of a fast diagnosis device for COVID-19 infection using a combination of DNA/RNA aptamer and antibodies on a nitrocellulose membrane.

Fig. 2

S-DNA-aptamer conjugation to gold nanoparticles: A) Snap of the gold-nanoparticle gel; B) Ethidium bromide channel; C) Cy3-channel. 1. 1 kb ladder; 2. Bare gold nanoparticles; 3. Gold + Cy3-DNA; 4. Gold-DNA-aptamer for spike protein; 5. Gold-DNA-aptamer + Cy3-DNA; 6. Gold-DNA-aptamer for nucleocapsid-protein; Gold-DNA-aptamer for nucleocapsid protein + Cy3-DNA.

Fig. 3

Concertation limit determination: S-antibody anchored on the nitrocellulose membrane is titrated against S-aptamer conjugated gold nanoparticles through thiol chemistry, after their incubation with s-protein solution from 250 ng/μl to 0 ng/μL.

Fig. 4

Concertation limit determination: S-antibody anchored on the nitrocellulose membrane is titrated against S-aptamer conjugated gold nanoparticles through biotin and streptavidin interaction, after their incubation with s-protein solution from 250 ng/μl to 0 ng/μL.

Fig. 5

Photographs of LFA strips used to test S-protein samples using DNA-aptamer conjugated gold nanoparticles in physiological buffers. A) LFA result of S-protein samples in various physiological buffers (1. 1× PBS, 2. 20 % FBS, 3. Cell culture media, respectively) using gold nanoparticle conjugated to DNA aptamer through thiol chemistry. B) LFA result of S-protein samples in various physiological buffers (4. 1× PBS, 5. 20 % FBS, 6. Cell culture media, respectively) using gold nanoparticle conjugated to DNA aptamer through biotin-streptavidin interaction.