Deuterium oxide or heavy water (D 2 O) is an isotopically labeled version of regular water (H 2 O) and is vital for a wide range of applications, including chemical analysis and medicine. However, because it is almost identical in size and shape to regular water, discrimination between these two water variants is tremendously difficult. Currently, only cumbersome laser-based methods are able to detect low levels of H 2 O contamination in D 2 O. No convenient technology allows the rapid, point-of-need sensing of trace water in D 2 O. Here, we report on a solution to this unsolved problem.

Our solution relies on a unique family of luminescent materials. These lanthanide-based systems function as highly accurate solid-state sensors that can quantitatively detect H 2 O in D 2 O from 10 to 120,000 ppm. These sensors can also detect trace H 2 O in a variety of common solvents that typically present problems for conventional sensing methods, such as Karl-Fischer analysis.