The methods for detecting and diagnosing COVID-19 are often unreliable or too expensive and complicated. A new technique has been developed using “slow light” that enables simple detection and quantification of virus particles using a basic optical microscope and readily available antibody proteins.
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Visualizing Nanoscale Coronavirus Particles is a Technical Challenge
At the outbreak of the COVID-19 pandemic in late 2019 and early 2020, the world research and health communities galvanized to develop solutions on a large scale quickly.
Effective public health policies were drawn up and implemented quickly and effectively. Vaccines were developed in record time and testing solutions were made available in many parts of the world.
However, the primary testing solutions – polymerase chain reaction (PCR) and rapid diagnostic tests – are limited. Neither test is entirely accurate, particularly rapid tests, and PCR tests are expensive and time-consuming.
Virus particles are only nanometers across and have low refractive indices. This leads to weak light-matter interactions, making it difficult to observe and analyze nanoscale bioparticles optically. This is why the commonly available COVID-19 tests have low accuracy.
The scientific community has recently developed solutions to this challenge, visualizing nanoscale coronavirus particles with near-field optical microscopy, ultra-high-resolution microscopy, electron microscopy, and several advanced, novel techniques.
However, these methods for nanoscale imaging all require complex or even bespoke equipment, high-powered data processing software, and specially trained operatives.
New Slow Light Research for Visualizing Virus Particles
In a groundbreaking study published in Advanced Materials in 2022, researchers at Korea’s Gwangju Institute of Science and Technology describe a novel technique for visualizing coronavirus particles with conventional optical microscopes.
The paper presents a new detection platform that exploits a nanoscale optical phenomenon known as slow light to detect nanoscale virus particles.
The method is called the “Gires-Tournois immunoassay platform,” or GTIP. GTIP works by slowing down reflected light’s velocity by shining it through a stack of thin-film materials. The materials are selected to cause a vivid color change with high chromatic contrast in the light when it passes through target particles.
Color changes can be automatically detected with 2D raster scanning based on chromaticity analysis.
The stack of thin-film materials in the GTIP is a Gires-Tournois resonance structure. It is made of three layers of materials that create the slow light phenomenon. Incident light rebounds inside the stack of materials before it is reflected, so the platform’s color appears uniform when viewed through an optical microscope.
Nanoscale virus particles affect the resonance frequency of light moving around them, slowing it down. The slow light shows a vivid color change on the optical microscope image, with clusters of virus particles appearing in sharp contrast against the uniform background.
Using the Slow Light Method for COVID-19 Detection
The researchers applied a coating of antibody proteins that only respond to SARS-CoV-2 on the top layer of the GTIP to ensure it only detected the target coronavirus particles.
As well as enabling the detection of coronavirus particles, the GTIP provided enough data for researchers to perform colorimetric analysis to effectively quantify target virus particles in different areas of the sample. This means that the GTIP can accurately and reliably detect the presence of the SARS-CoV-2 virus in samples.
The GTIP design benefits from a high level of simplicity. Extra sample treatments such as amplification and labeling are not required, and tests can be performed on-demand at the point of care.
As well as being suitable for any laboratory with a basic optical microscope, the GTIP can also be deployed in the face masks recommended for tackling the COVID-19 pandemic. Researchers demonstrated how the GTIP can be attached to a facemask and used to detect coronavirus particles sprayed from a conversational distance away from the wearer.
Schematic illustration of GTIP-attached face protection mask. f) Viral fluid spraying at droplet transmission distance (≈1.3 m). g) Cluster pixel distribution of the viral fluid spraying test (1 ng mL−1). Image Credit: Yoo, Y.J., et al.
What are the Advantages of Exploiting Slow Light?
The GTIP provides numerous advantages over conventional approaches for detecting virus particles, building on slow light research.
The GTIP does not require any specialized instrumentation with its optical design. Laboratories can use standard bright-field microscopes along with the analyte and GTIP resonator.
The platform also eliminates the need for repetitive detection processes. This is because different specific target antibodies can be applied to an array of multiple sensing areas.
The method is also not limited by immune binding, the detection method for virus particles such as coronavirus. Any binding agent attached or coated to the surface will illuminate and amplify light-matter interactions with the analyte.
Finally, the method can be applied to fluid dynamic monitoring and detection of target particles sprayed in the air or dispersed on surfaces in various different forms.
The researchers are now focused on overcoming some remaining and minor limitations for the GTIP while also seeking to establish the platform as an invaluable tool for simple, multiscale imaging and detection of virus particles with no unique treatments required.
Their success would be a breakthrough for public health worldwide, not just by tackling the ongoing COVID-19 pandemic but also by enabling rapid, cheap, and accurate detection of numerous other viruses and target nanoparticles.
References and Further Reading
Researchers detect coronavirus particles with “slow light.” (2022) [Online] ScienceDaily. Available at: https://www.sciencedaily.com/releases/2022/04/220421094151.htm (Accessed on 16 May 2022).
Shining a Light on COVID-19. (2020) Nature Photonics. doi.org/10.1038/s41566-020-0650-9.
Won, R. (2020). Machine intelligence lights up imaging. Nature Photonics. doi.org/10.1038/s41566-020-0627-8.
Yoo, Y.J., et al. (2022). Gires–Tournois Immunoassay Platform for Label-Free Bright-Field Imaging and Facile Quantification of Bioparticles. Advanced Materials. doi.org/10.1002/adma.202110003.