Skip to main content
Premium Trial:

Request an Annual Quote

WUSTL Team Develops Highly Sensitive Lateral Flow Testing Method


NEW YORK – Although lauded for their ease of use and speed, a consistent complaint against lateral flow tests — particularly throughout the COVID-19 pandemic — has been the lack of sensitivity. 

A team of researchers from Washington University in St. Louis say that by integrating a new particle into traditional lateral flow tests, they may have solved the issue. The team created the plasmonically active antibody-conjugated fluorescent gold nanorods, or plasmonic fluors, which are nearly 7,000 times brighter than conventional fluorophores, providing for greater interrogation into the presence of a pathogen.

Developed at the start of the pandemic, according to Srikanth Singamaneni, a professor of mechanical engineering and materials science at the university, the researchers were originally focused on applying the plasmonic fluors in laboratory-based tests, but as the pandemic continued, they recognized the need for more sensitive lateral flow tests that are used at the point of care. When translating the method to lateral flow testing, the researchers figured the assay format could be kept virtually the same by trading out the colloidal gold nanoparticles used in many lateral flow tests for the plasmonic fluors, Singamaneni said. 

The benefit of doing so, he added, is that only 100 plasmonic fluors can generate a detectable signal compared to approximately 1 million colloidal gold nanoparticles.

The field has long known that plasmonic structures can amplify fluorescence, but many researchers have attempted to implement new assays on top of plasmonic structures, rather than using them in existing tests. The Wash U team instead decided to "simply create a label that comes in the end and amplifies the signal, rather than asking them to change the whole assay protocol," he said. 

The plasmonic fluors act as both colorimetric and fluorescent reporters within the lateral flow tests the researchers developed, as explained in a paper published in Nature Biomedical Engineering earlier this month. The team optimized the fluors to detect interleukin-6, SARS-CoV-2 S1 antibodies, and the SARS-CoV-2 nucleocapsid protein and validated the tests with plasma, serum, and nasopharyngeal samples, according to the paper. The team previously explained the development of the fluors in a paper published in Nature Biomedical Engineering in 2020.

By using them as colorimetric reporters, the plasmonic fluors provide a visual result indicating whether a sample is positive or negative, similar to a traditional lateral flow test and with equivalent sensitivity. However, by using a scanner to detect fluorescence, the fluors can provide a quantitative measurement — useful when looking for concentrations of a particular biomarker, such as interleukin-6. The scanner also significantly enhances the sensitivity of the test, Singamaneni said. 

For interleukin-6, the fluorometric test showed a 1,785-fold improvement in the limit of detection compared to conventional gold particle-based colorimetric tests. 

When detecting SARS-CoV-2 antibodies, the test with the plasmonic fluors was 96 percent sensitive in 79 samples, while also showing 100 percent specificity. Compared with conventional sandwich ELISA tests, the fluorometric test showed 165-fold improvement in the limit of detection, the researchers noted.

Meantime, when detecting SARS-CoV-2 antigens with the fluorescent scanner, the sensitivity was 95 percent in 19 samples. The researchers compared the fluorometric version of the test to the colorimetric version of the test and to Becton Dickinson's BD Veritor antigen test, which both had a sensitivity of 42 percent in the same 19 samples. The researchers then tested an additional 16 samples with the Delta variant and 17 samples with the Omicron variant, and the assay was able to pick up all but one of those samples. 

Although adding the reader takes away some of the convenience of a traditional antigen test, Singamaneni said the improvements in sensitivity and the ability to provide a quantitative answer are worth it. While there "might be some resistance" because the test isn't intended for visual detection, "visual detection comes with its own limitations," he said. 

In some cases, particularly when it comes to infectious diseases, users are looking for a positive or negative result, but in many other applications a quantitative measurement is important, such as in kidney disease, he noted. Kidney disease is one of the applications the researchers are looking into for the method, he added. 

In the most recent paper, the researchers used both a benchtop fluorescent scanner, which takes about four hours to return results, and a portable reader developed by the team, which takes about 20 minutes to return results. The portable scanner costs about $1,429 and can be used multiple times, but Singamaneni said it can be miniaturized and optimized with less expensive parts to bring the price down to about $300. The team is also hoping to further miniaturize the reader, potentially getting it down to a size that could be attached to a smartphone. 

One future goal for the researchers is to see if they can integrate RNA detection and antigen detection on a single lateral flow strip to determine if a patient is not only infected but also actively infectious, he said. Despite that goal and that the team's first application of the technology is COVID-19, Singamaneni said they're also focusing on other diseases, particularly sexually transmitted infections — an area lacking reliable antigen tests, he noted. 

"The sensitivity of most of the existing tests is very poor, so they're not even being used," he said. "If we can actually take this technology … to some of those diseases, I think we can transform the diagnostic space in those diseases."

Tuberculosis is another area of focus for the team, as many low- and middle-income countries have a need for accurate and lower-cost tuberculosis tests, he said. 

The technology has been licensed to Auragent Biosciences and CEO Shaker Sadasivam said via email that the company is developing an integrated point-of-care platform using the technology.