Physics Boosts Fentanyl Detection Strip Sensitivity

Researchers develop a physics-based model to improve performance of competitive lateral flow assays

Mar. 25, 2026 at 2:05am

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Researchers from the University of California, San Diego have developed a physics-based model to explain the performance and sensitivity limits of competitive lateral flow assays (cLFAs), a category of test strips used to detect the presence of specific molecules like drugs or viruses. They applied this model to improve commercially available fentanyl test strips, making them about 100 times more sensitive than before.

Why it matters

The lack of a clear, quantitative way to explain the sensitivity ceiling of lateral flow assays has been a longstanding challenge, especially during the COVID-19 pandemic when these tests were used at an unprecedented scale. This new physics-based model provides a unified framework to optimize the sensitivity of cLFAs, which could help accelerate development and improve performance of these point-of-care tests across many applications, from detecting fentanyl to screening for sexually transmitted infections.

The details

In competitive lateral flow assays, the lack of a test line indicates a positive result. Antibodies attached to gold nanoparticles wait to bind with the target molecule, but if the sample contains the target, those molecules will bind the antibodies first, preventing the gold nanoparticles from producing a visible signal at the test line. The researchers developed a mathematical relationship between factors like the concentrations of target molecules, antibodies, and gold nanoparticles, as well as their binding affinities, that can be optimized to improve the limit of detection for cLFAs.

  • The research was published on March 24, 2026 in Biophysics Reviews by AIP Publishing.

The players

Yuhwa Lo

The lead author of the study and a researcher at the University of California, San Diego.

University of California, San Diego

The institution where the researchers who developed the physics-based model for improving lateral flow assays are based.

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What they’re saying

“This limitation became especially apparent during the COVID-19 pandemic. Antigen LFAs were used at an unprecedented scale, but there was still no clear, quantitative way to explain the sensitivity ceiling or to answer practical questions, such as whether — and under what conditions — LFAs could realistically approach the sensitivity of laboratory nucleic acid tests.”

— Yuhwa Lo, Researcher

“This kind of universality is powerful. A single, unified framework can provide clear, actionable guidance for sensitivity optimization across many cLFAs, helping accelerate development and improve performance throughout the field.”

— Yuhwa Lo, Researcher

What’s next

The researchers hope to extend their physics-based model to sandwiched lateral flow assays, which include pregnancy and COVID-19 tests, in order to further strengthen the reliability of existing point-of-care tests and expand what can be detected outside of centralized laboratories.

The takeaway

By developing a quantitative, physics-grounded method for explaining the sensitivity and limits of competitive lateral flow assays, researchers have provided a unified framework to optimize the performance of these ubiquitous point-of-care tests, which could enable rapid screening for a wider range of clinically important targets beyond just fentanyl detection.