Metal-Enhanced Fluorescence-Based LFI Platform Detects Influenza A Virus in 20 Minutes

Throughout history, as evidenced by the influenza epidemic during World War I, the MERS-CoV outbreak in the 2010s, and the recent COVID-19 pandemic, it has become clear that viral respiratory diseases emerge recurrently. Factors like dense populations, close interactions during travel, and enhanced global connectivity have all contributed to the faster spread of these infections. For the prompt management and containment of such outbreaks, there is a critical need for rapid diagnostic methods that can quickly detect the presence of viruses, which allows for timely isolation and treatment of affected individuals. Fluorescence-based lateral flow immunoassay (LFI) methods have gained popularity as a rapid viral detection mechanism. They rely on the emission of light from specific molecules when they come into contact with viral particles. However, this method has its limitations, particularly related to sensitivity to detect the presence of viruses.

To address the limitations of existing rapid tests, scientists at Gwangju Institute of Science and Technology (GIST, Gwangju, South Korea) have enhanced the capabilities of fluorescence-based LFIs with the introduction of gold nanorod (GNR)-enabled probes. The team engineered probes with a layered core–shell structure called Cy5-mSiO2@GNR, composed of a central GNR core, a mesoporous silica (mSiO2) outer shell, and the fluorescent dye cyanine 5 (Cy5). This novel design counters the usual drawbacks of fluorescence-based LFI such as the quick fading of fluorescent signals and low light emission efficiency through metal-enhanced fluorescence (MEF).

Image: A highly sensitive lateral flow immunosensor with mesoporous silica-coated gold nanorods (Photo courtesy of GIST)

The research team thoroughly analyzed these Cy5-mSiO2@GNR probes, testing their fluorescence in response to different shell thicknesses around the GNR. They identified an optimal thickness of the silica shell at 10.3 nm, setting this as the standard for achieving the most effective enhancement in fluorescence. Utilizing this MEF technique, the researchers successfully demonstrated the use of their optimized probes in an LFI setup for detecting the influenza A virus (IAV).

With the enhanced fluorescence provided by the MEF approach, the LFI system could identify IAV at very low virus concentrations, detecting the virus in as little as 20 minutes. It proved highly specific, able to differentiate IAV even amidst other viruses such as MERS-CoV and SARS-CoV-2, responsible for COVID-19. Furthermore, the system showed exceptional accuracy, over 99%, when identifying IAV in samples taken from patients. This improved Cy5-mSiO2@GNR-based LFI platform presents a significant advancement for point-of-care diagnostics, offering a robust solution for the early and accurate detection of IAV, among other viruses, especially in emergency situations.

“The findings of this research can not only transform rapid testing in healthcare, but its scope can be also extended to other forms of biomolecule diagnostics, with the ultimate goal of improving people’s quality of life,” said Professor Min-Gon Kim from the Department of Chemistry at GIST who led the research.

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