Paper Strip Saliva Test Detects Elevated Uric Acid Levels Without Blood Draws

Diagnosing elevated uric acid (UA) levels—an important indicator for conditions like gout, chronic kidney disease, and metabolic syndrome—typically requires blood draws, lab equipment, trained technicians, and expensive reagents. These conventional diagnostic methods are invasive, time-consuming, and inaccessible for daily monitoring or use in remote settings. Patients often lack affordable, non-invasive options for quick UA screening at home. Now, researchers have developed a paper-based test that provides instant, lab-free detection of UA levels using just a drop of saliva and a smartphone.

Scientists from Shaanxi University of Science and Technology (Xi'an, China) have created “abnormal UA alarm,” a paper strip embedded with naphthylimide-derived fluorescent microparticles (NIFS) anchored to cellulose fibers. In water, these particles self-assemble into glowing lamellar structures under UV light, which dim proportionally when uric acid is present due to hydrogen bonding between the dye and UA. The darker the fluorescence, the higher the uric acid concentration. A smartphone app captures the color shift and calculates UA concentration by reading changes in the green channel of RGB values. The strip is entirely enzyme-free, electricity-independent, and integrates with a compact, credit-card-sized dark box that snaps onto smartphones, making the device user-friendly and highly portable.

Image: The fluorescent “abnormal UA alarm” delivers smartphone-guided, enzyme-free gout screening for pennies per test (Photo courtesy of Shaanxi University)

A laboratory validation study, published in the Journal of Bioresources and Bioproducts, showed that the test detects UA concentrations as low as 0.91 μmol/L—well below the 250 μmol/L salivary threshold linked to hyperuricemia. Even when exposed to 34 common interferents like salts, amino acids, glucose, and dopamine, the strip’s fluorescence change remained UA-specific. In tests using real saliva, artificial urine, and food extracts, the tool yielded results with 95% to 108% accuracy, matching traditional hospital assays. The strips are stable for at least six months at room temperature and cost less than one U.S. cent to produce. Researchers aim to launch an open-source testing kit later this year, with applications envisioned for use in homes, pharmacies, gyms, and low-resource clinics.

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Shaanxi University of Science and Technology