Researchers have developed a new biosensor that uses color changes to detect urea levels in fluids such as urine, offering a sensitive and easy-to-read option for potential use in clinical and environmental settings. The study, published in Microsystems & Nanoengineering, describes a method based on the chemical etching of gold nanobipyramids (AuNBPs), which visibly change color in response to urea concentration.
The sensor works by taking advantage of how urea breaks down in the presence of an enzyme called urease. As urea is broken down, ammonia is released, raising the pH of the solution. This pH change slows a chemical reaction known as the Fenton reaction, which normally dissolves the gold nanobipyramids. When etching slows, the particles maintain their shape longer, resulting in a color shift that can be seen with the naked eye.
The researchers designed both a liquid-based and a solid, agarose-based version of the sensor. Both formats showed a wide range of distinct colors – ranging from pink to brown – depending on the amount of urea present. In lab tests, the sensor could detect urea in concentrations as low as 0.098 μM in solution and 0.2 μM in solid form.
Tests on urine samples from two volunteers showed that the sensor could accurately estimate urea levels even when the samples were diluted 400 times. The color changes remained clear, and the results closely matched those from a commercially available urea test kit. The multicolor output also allowed for an added quality control feature: if the sensor failed to change color in the expected way, users could detect malfunction or reagent degradation simply by eye.
Of note, the sensor was not affected by other substances commonly found in urine, such as creatinine or glucose, which suggests it could provide specific and reliable results in complex biological samples.
While further testing is needed to explore broader applications, the authors suggest this sensor could support point-of-care diagnostics or environmental monitoring where quick, simple urea testing is needed without advanced equipment.
Newsletters
Receive the latest pathologist news, personalities, education, and career development – weekly to your inbox.
