Direct Virus Capture Assay for Label-Free Detection of SARS-CoV-2 Virions Using Laser Microscopy

Abstract

Aim: To evaluate a label-free and variant-independent assay called direct virus capture (DVC) for detection of intact SARS-CoV-2 virions through light scattering, utilizing an optical inverted laser microscope called nano eye device virus detector (NED-VD). Methods: The DVC assay involves the interaction between ACE2 receptors printed on a glass coverslip substrate, and the S protein on the outer surface of virions. The study was conducted using 191 human swab specimens. Results: In comparison to the RT-PCR assay, the DVC method achieved a sensitivity of 40.5%, specificity of 90.4% and accuracy of 46%. Conclusion: The study presents a promising qualitative pre-screening test to evaluate the presence of whole virions and reduce the number of PCR tests.

Plain language summary

SARS-CoV-2, the virus responsible for the COVID-19 pandemic, can spread quickly from person to person and can make people very ill. An important part of controlling the spread of the virus is to detect infections early through diagnostic tests. This study presents a new test called direct virus capture (DVC). In this test, the virus is frozen on a glass slide and visualized with a laser microscope. We tested samples from 191 patients using DVC and the most common diagnostic test for SARS-CoV-2. Both methods identified the virus in the samples, but DVC was able to capture the whole intact virus. Only in this form is the virus able to attack human cells and cause disease.

Keywords: :

• biosensing
• intact virions
• label-free
• microscopy
• SARS-CoV-2
• scattering

Author contributions

A Pennesi: writing – original draft, data curation, visualization. G Ferrari: validation, investigation. F Giardina: validation, resources, investigation. S Piselli: investigation. R Lo Savio: formal analysis, writing – review and editing. A Carloni: conceptualization, methodology, writing – review and editing, project administration. S Paolucci: supervision, project administration. F Baldanti: supervision, project administration.

Acknowledgments

The authors thank M Pizzato and C Bertelli (department of cellular, computational and integrative biology, University of Trento) for their contribution to the early development stages of DVC assay and the preparation of the pseudotyped HIV-1 virions.

Financial disclosure

This study was funded by NTP Nano Tech Projects srl. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Competing interests disclosure

The assay tested in this study is currently in development at NTP Nano Tech Projects. The authors have no other competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript apart from those disclosed.

Writing disclosure

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

This study was approved by the ethics committee of Fondazione IRCCS Policlinico San Matteo, Pavia, Italy (#43923/2021).