Revolutionary “Coffee Ring” Test Promises 100x More Sensitive At-Home Disease Detection
A new, low-cost biosensing technology developed at the University of California, Berkeley, could dramatically improve the accuracy of rapid at-home tests for illnesses ranging from COVID-19 to prostate cancer and sepsis. The breakthrough leverages a common phenomenon – the “coffee ring effect” – combined with advanced plasmonics and artificial intelligence to detect disease biomarkers with unprecedented sensitivity.
The increasing popularity of at-home tests has offered convenience in determining whether symptoms are due to a serious illness or a minor ailment like seasonal allergies. However, current at-home tests often lack the sensitivity of those administered in a clinical setting, leading to potential false negatives. Researchers are now aiming to address this limitation with a technology that could represent a significant leap forward in point-of-care diagnostics.
Harnessing the Power of the “Coffee Ring Effect”
The core of this innovation lies in the “coffee ring effect,” a physical phenomenon easily observed in everyday life. As a droplet of liquid evaporates, dissolved particles are drawn towards the edges, creating a concentrated ring-like stain. Researchers discovered that this principle could be harnessed to concentrate disease biomarkers, making them easier to detect.
“This simple yet effective technique can offer highly accurate results in a fraction of the time compared to traditional diagnostic methods,” explained a researcher involved in the project. “Our work paves the way for more affordable, accessible diagnostics, especially in low-resource settings.”
The technology was born from an unexpected observation during COVID-19 biosensor development in 2020. A researcher noticed ring-shaped stains forming as experimental solutions dried, sparking the idea of utilizing the effect to concentrate viral particles. “We figured out that we could use this coffee-ring effect to build something even better than what we initially set out to create,” the researcher added.
How the Test Works: Plasmonics, Nanoparticles, and AI
The new diagnostic test utilizes plasmonic nanoparticles – tiny particles that interact with light in unique ways. The process involves two key steps:
- A sample containing disease-relevant proteins, obtained from a swab (cheek or nasal), is applied to a membrane. As the droplet dries, biomarkers are concentrated at the resulting “coffee ring.”
- A second droplet containing engineered plasmonic nanoparticles, designed to bind to the biomarkers, is added. If biomarkers are present, the nanoparticles aggregate in patterns that alter how light interacts with the membrane.
This change in light interaction can be detected visually or through an AI-powered smartphone app, providing results in under 12 minutes. The technology demonstrates a sensitivity 100 times greater than existing rapid tests for COVID-19.
Beyond COVID-19: Expanding Diagnostic Capabilities
The potential applications of this technology extend far beyond COVID-19. Researchers have identified a key protein biomarker for sepsis, a life-threatening inflammatory response to bacterial infection, that can be detected using this method. Currently, diagnosing sepsis relies on bacterial cultures, a process that can take several days.
“Every hour is critical [in sepsis cases], but culturing bacteria to determine the source of the infection can take a few days,” stated Liwei Lin, a Distinguished Professor of Mechanical Engineering at UC Berkeley and senior author of the study. “Our technique could help doctors detect sepsis in 10 to 15 minutes.”
The team envisions the technology being used for early detection of other serious conditions, including prostate cancer, enabling more accessible and regular screening. A prototype home testing kit, similar in design to existing COVID-19 tests and incorporating 3D-printed components, has already been developed.
“During the COVID-19 pandemic, we relied on at-home tests to know if we were infected or not,” Lin said. “I hope that our technology makes it easier and more accessible for people to regularly screen for conditions like prostate cancer without leaving the home.”
The research, published in the journal Nature Communications in July 2025, was supported by seed funding from the CITRIS and Banatao Institute at UC Berkeley. The study’s co-authors include Zahra Khodabakhshi Fard, Chun-Ming Chen, Peisheng He, and Megan Teng of UC Berkeley.
Source: University of California – Berkeley
Journal reference: Behrouzi, K., et al. (2025). Plasmonic coffee-ring biosensing for AI-assisted point-of-care diagnostics. Nature Communications. doi.org/10.1038/s41467-025-59868-y.
