Paper strip turns saliva into instant uric-acid alert, replacing needles and lab visits

A team led by Professors Hui’e Jiang and Zhijian Li at Shaanxi University of Science and Technology has turned a scrap of filter paper into a pocket laboratory that can diagnose elevated uric acid levels without blood draws, reagents or electricity. Described in the Journal of Bioresources and Bioproducts, the “abnormal UA alarm” consists of naphthylimide-derived fluorescent micro-particles (NIFS) anchored to cellulose fibres. In water, NIFS self-assemble into lamellar aggregates that emit an intense blue-green glow under a 365 nm UV torch. When uric acid is present, hydrogen bonding between UA and the dye quenches the fluorescence; the darker the paper becomes, the higher the UA concentration. A custom smartphone app reads the red-green-blue (RGB) values of the spot and converts the green-channel drop into a precise concentration within seconds.

Laboratory validation showed the paper strip can quantify UA from 0 to 5 000 μmol L⁻¹ with a limit of detection of 0.91 μmol L⁻¹—well below the 250 μmol L⁻¹ salivary threshold associated with hyperuricemia. Even in the presence of 34 common interferents—including salts, amino acids, glucose and dopamine—the signal change remained UA-specific. Tests on real human saliva, artificial urine and food extracts returned recoveries between 95 % and 108 %, matching hospital enzymatic assays without the need for temperature-controlled reagents or trained technicians.

Because the platform is enzyme-free, the strips remain stable for at least six months at room temperature and cost less than one U.S. cent each to produce. Researchers envision the technology enabling daily self-monitoring for patients with gout, chronic kidney disease or metabolic syndrome, as well as rapid screening in pharmacies, gyms and remote clinics. The team is now integrating the reader into a credit-card-sized dark box that snaps onto a mobile phone, aiming to release an open-source kit later this year.

See the article:

DOI

https://doi.org/10.1016/j.jobab.2025.06.002.

Original Source URL

https://www.sciencedirect.com/science/article/pii/S2369969825000398

Journal

Journal of Bioresources and Bioproducts