Scientists at the Indian Institute of Science (IISc) have created an innovative luminescent sensor that uses terbium—a rare earth metal—to detect the enzyme β-glucuronidase, a potential biomarker for liver cancer. The findings, published in the journal Chemistry, offer a promising approach for cancer diagnostics, especially in low-resource settings.
β-glucuronidase is a highly conserved enzyme found across various organisms, from microbes to humans. It plays a vital role in breaking down glucuronic acid, a sugar derivative. More importantly, elevated levels of this enzyme have been linked to several diseases, including liver, breast, colon, and kidney cancers, as well as urinary tract infections and AIDS.
“Traditional detection methods such as colorimetry and standard fluorescence often face limitations due to poor sensitivity or interference from background signals,” said Ananya Biswas, former PhD student at IISc and co-first author of the study. “Rare earth metals like terbium have long-lived excited states, allowing us to filter out short-lived background noise and produce a much clearer signal.”
The research team had been exploring the properties of metal ions and gels for nearly a decade. They discovered that terbium ions embedded in a gel made from bile salts produce a green fluorescence. Building on this, they introduced a compound called 2,3-Dihydroxynaphthalene (2,3-DHN), which was chemically modified by attaching glucuronic acid—making it responsive to β-glucuronidase activity.
When the enzyme is present, it cleaves off the glucuronic acid, releasing free 2,3-DHN. Upon exposure to UV light, this molecule acts as a light-harvesting antenna, absorbing the energy and transferring it to nearby terbium ions in the gel matrix. The result is a significantly enhanced green glow.
“This efficient energy transfer is made possible by the gel matrix, which keeps the terbium ions and the antenna molecule in close proximity,” explained Uday Maitra, honorary professor at IISc’s Department of Organic Chemistry and corresponding author of the study.
To simplify its use, the researchers developed a paper-based version of the sensor by embedding the gel into a small disc. When the modified 2,3-DHN is added along with β-glucuronidase, the paper glows brightly under UV light.
What sets this technique apart is its accessibility. Instead of relying on expensive lab equipment, the glowing signal can be analyzed using a standard UV lamp and ImageJ, a free, open-source image analysis software—making it ideal for deployment in resource-constrained environments.