Applications of bioconjugated nanomaterials in SARS-CoV-2 diagnostics

In a new study in the journal Accounts of Materials Research, researchers presented an overview of the recent advances in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-targeted diagnoses using bioconjugated nanomaterials. They discussed surface functionalization of nanomaterials, different powerful platforms currently explored for testing and concluded with significant challenges in the field.

Study: Bioconjugated Nanomaterial for Targeted Diagnosis of SARS-CoV-2. Image Credit: Kateryna Kon/Shutterstock

Introduction

Pandemics have caused huge mortality, accompanied by global economic crashes and poverty. The ongoing pandemic coronavirus disease 2019 (COVID-19), caused by the SARS-CoV-2, is responsible for over 5.4 million deaths worldwide and continues into its third year with the emergence of new variants.

To break the infection spread and mitigate the disease, it is crucial to implement diverse strategies – one of which is detecting the infected, who can then be isolated and given appropriate care for rapid recovery. Presently, the gold standard for SARS-CoV-2 diagnosis is the reverse transcriptase-polymerase chain reaction (RT-PCR), which is time-consuming. Other diagnoses techniques currently used are reverse-transcription loop-mediated isothermal amplification (RT-LAMP), clustered, regularly interspaced short palindromic repeats (CRISPR), enzyme-linked immunosorbent assay (ELISA), lateral flow assay (LFA), etc.

However, a quick mass-testing tool is essential to check it before the infectious disease gets out of control during the pandemic. To this end, advanced materials are potential tools to develop a SARS-CoV-2- targeted diagnosis that can be a modular method for any infectious disease.

These nanomaterials with tunable optical, electrical, magnetic, structural, and functional properties, and bioconjugated with antibodies, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), or peptide aptamers, are extensively researched to develop a successful platform with high targeting efficiencies and reduced nonspecific interactions. The present study summarizes the recent advances in the bioconjugated nanomaterial-based approaches for effectively diagnosing COVID-19 and the SARS-CoV-2 viral RNA, antigen, or antibody.

Tailoring the surface functionalities of nanomaterials

Surface functionalization is a crucial step to develop a bioconjugated material for the targeted diagnosis of the virus – to be highly sensitive and specific for measuring the virus RNA, antigens (S or N protein), or antibodies (immunoglobulins, IgA, IgM, IgG).

For point-of-care settings with mass-testing or even for home daily use kits that can test rapidly, maybe even 5 mins, researchers worldwide are trying to develop an easy-to-use calorimetric diagnostic testing. Plasmonic gold nanoparticles with higher extinction coefficients (∼10⁹ for 20 nm nanoparticles) and the absorption and scattering falling within the visible spectrum are common for this purpose.

However, bioconjugated nanomaterials are designed by manipulating the biomolecular recognition events to reduce nonspecific binding. Strategies such as coating the nanomaterial with polyethylene glycol (PEG) (to reduce charge and nonspecific binding) before conjugating with the targeting agents such as the SARS-CoV-2-specific antibody or DNA/RNA/peptide aptamer are carried out.

The nanomaterials employed in this purpose, conjugated with nucleic acids- or proteins-based detection, are a bioconjugated zero-dimensional (0D) spherical gold nanoparticle, quantum dots, one-dimensional (1D) carbon nanotubes (CNTs), nanorods, and two-dimensional (2D) graphene.

Recent advances in the bioconjugation design

It is important to develop a powerful platform for naked-eye detection through colorimetry using plasmonic nanoparticles. The present research group has reported bioconjugated nanomaterial-based naked eye colorimetric diagnosis of SARS-CoV-2, rotavirus, dengue virus, and different superbugs as Carbapenem-resistant Enterobacteriaceae (CRE) Escherichia coli, Salmonella DT104, and methicillin-resistant Staphylococcus aureus (MRSA).

Within ten minutes, bioconjugated gold nanoparticles detect SARS-COV-2 by agglomerating in the presence of RNA sequence of SARS-CoV-2 by measuring the localized surface plasmon resonance (LSPR) and provide a naked-eye detection. It is reported that a viral load corresponding to the threshold cycle (Ct) = 36.5 can be detected using this assay.

Recently, the CRISPR/Cas12a and CRISPR/Cas13a systems, conjugated with gold nanoparticles, are designed for the rapid and sensitive detection of SARS-CoV-2, with potential for SARS-CoV-2 screening in clinics where state-of-the-art facilities are lacking.

Lateral flow assay (LFA) using bioconjugated gold nanoparticles is used to detect antibodies generated in the body after a viral infection. Though this assay can not be used for immediate detection, it is a good method for mass-scale testing of clinical samples; it has an accuracy of 100%.

However, due to the low sensitivity of the gold nanoparticles-based assay, researchers further developed ultrasensitive tools. A highly sensitive Surface-Enhanced Raman Scattering (SERS)-, fluorescence and nanoparticle surface energy transfer (NSET)-based on specific and rapid diagnosis of the SARS-CoV-2 viral antigens, RNA viruses, and other viruses are discussed in detail.

Identifying SARS-CoV-2 infections via CNT, quantum dots (QDs), and plasmonic nanoparticles is now well-established. The Raman bands from pseudo-SARS-CoV-2 are reported to be assigned to the spike protein phenylalanine ring breath mode, amide II, and amide III modes.

A recent study has demonstrated the capability of the antibody-attached gold nanoparticle-based SERS for fingerprint identification of dengue, West Nile, rotavirus, and coronavirus – the major Raman Bands observed in the SERS spectra are listed here. The gold nanoparticle-based SERS assay can detect the SARS-CoV-2 antigen within 20 mins, with an accuracy of 87.7%. The assay can diagnose 1 pg/mL antigen.

Further, carbon dots (CDs), perovskite quantum dots (PQDs), semiconductor quantum dots, and lanthanum nanoparticles are used as fluorescent probes with higher quantum yield and are resistant to photobleaching. These materials are used for nanoparticle-based sensors for SARS-CoV-2 sensing. The ACE2-SWCNT nanosensor is specifically developed for SARS-CoV-2 spike sensing from the fluorescence spectrum to test from saliva, nasal fluid, and sputum samples.

Discussing the basics of Förster or Fluorescence Resonance Energy Transfer (FRET)-technology, the researchers in the Account go on to cite the uses in SARS-CoV-2 detection. For example, the NSET and aptamer-based biorecognition technology – where they have developed rhodamine 6G (Rh-6G) dye-conjugated COVID-19 spike protein-specific DNA aptamer-attached gold nanostar-based NSET for rapid diagnosis of the COVID-19 antigen or virus.

Conclusion

In this study, the researchers not only elucidate the recent bioconjugated nanomaterials for targeted diagnosis of SARS-CoV-2, but they also provide the rationale behind these developments by discussing the mechanisms and approaches. The study listed the bioconjugated nanostructure used in the design of the bioconjugated nanomaterials, including the target molecule, detection platform, detection time, and sensitivity.

The major fundamental challenge in this field towards developing a SARS-CoV-2 targeted detection system is the development of cost-effective, biocompatible, and environmentally friendly nanomaterials, which simultaneously exhibit high selectivity and sensitivity, accuracy, and precision for real-life infectious disease marker sensing applications.