Aptamers-Diagnostic and Therapeutic Solution in SARS-CoV-2

Abstract

The SARS-CoV-2 virus is currently the most serious challenge to global public health. Its emergence has severely disrupted the functioning of health services and the economic and social situation worldwide. Therefore, new diagnostic and therapeutic tools are urgently needed to allow for the early detection of the SARS-CoV-2 virus and appropriate treatment, which is crucial for the effective control of the COVID-19 disease. The ideal solution seems to be the use of aptamers-short fragments of nucleic acids, DNA or RNA-that can bind selected proteins with high specificity and affinity. They can be used in methods that base the reading of the test result on fluorescence phenomena, chemiluminescence, and electrochemical changes. Exploiting the properties of aptamers will enable the introduction of rapid, sensitive, specific, and low-cost tests for the routine diagnosis of SARS-CoV-2. Aptamers are excellent candidates for the development of point-of-care diagnostic devices and are potential therapeutic tools for the treatment of COVID-19. They can effectively block coronavirus activity in multiple fields by binding viral proteins and acting as carriers of therapeutic substances. In this review, we present recent developments in the design of various types of aptasensors to detect and treat the SARS-CoV-2 infection.

Keywords: COVID-19; SARS-CoV; aptamers; aptasensors.

Figure 1

Structure of the SARS-CoV-2 virion. A single particle of the virus is composed of a lipid envelope encompassing structural proteins: S (spike), E (envelope), and M (membrane). Inside the virion, there is viral nucleic acid in a form of RNA, which is surrounded by N (nucleocapsid) proteins.

Figure 2

Structure of the SARS-CoV-2 genome (nsp—non-structural protein; RdRp—RNA-dependent RNA polymerase; UTR—untranslated region; ORF—open reading frame; E—envelope protein; M—matrix protein; N—nucleocapsid protein; RBD—region binding domain).

Figure 3

The structure of the SARS-CoV-2 S protein. It is a transmembrane protein composed of two subunits—S1 and S2—located on the outer side of the viral envelope, as well as transmembrane and inner fragments. The S1 protein subunit shows a trimeric structure and presence of the RBD (receptor-binding domain) responsible for the binding of the virion to the ACE2 (angiotensin-converting enzyme 2) receptor on the surface of infected cells.

Figure 4

The process of isothermal detection—general view. After the sample is obtained and prepared for testing, isothermal detection is performed. The process may use molecular probes or fluorescence aptamers, and the target of these molecules can be a nucleic acid (RNA or DNA) or a protein, respectively. The signal of the emitted fluorescence is detected by the detector, whose presence proves the occurrence of the molecule in the tested material.

Figure 5

Sensitive splint-based one-pot isothermal RNA detection—process flow. Both reactions take place in one tube. If the tested sample contains the genome (template) of the virus, the promoter and reporter probes will hybridize with it. The SplintR ligase combines the two probes for the first isothermal reaction. Then, T7 RNA polymerase transcribes from a fragment of genetic material that was created by combining both probes forming a second isothermal reaction. The resulting transcript is an aptamer specific to a fluorescent dye—after combining both molecules, fluorescence is emitted that can be detected.