In liquid form, life-saving agents such as vaccines can be notoriously unstable, often requiring refrigeration or other support systems to preserve them long enough to reach patients in need. International aid missions can easily be foiled by simple power outages ruining a batch of just such fragile medicine.

Researchers at McMaster University have developed a platform to overcome this problem, taking their inspiration from the chemistry of a consumer product: breath-freshening strips that melt on your tongue. The key ingredient in these strips is pullulan, a polysaccharide that becomes impermeable to oxygen after it dries. By casting enzymes and other substrates within this material, they can be preserved in a form that will remain inert until it interacts with water. “The process is very much like making gelatin,” says Carlos Filipe, a McMaster chemical engineering professor who was a principal investigator in this work. 

Filipe recalls how he and his colleagues were inspired by a doctoral student’s study of the breath strips as potential water-testing devices. Chemicals that would reveal the presence of pollutants could be stored in this stable form, which would remain viable for extended periods without any kind of elaborate packaging or storage conditions. 

This latest extension of the concept, described in an article published in Angewandte Chemie (Applied Chemistry) encapsulated two highly unstable agents — acetylcholinesterase and indoxyl acetate — as tablets in a robust assay kit for detecting pesticides in soil or water. This research was carried out through SENTINEL, a national network dedicated to creating real-time pathogen detection technologies based on bioactive paper. Founded after the 2003 severe acute respiratory syndrome (SARS) epidemic, which highlighted the lack of such technologies, the network was established by the Natural Sciences and Engineering Research Council in collaboration with several industrial partners. 

Filipe, for his part, admits that it took some time to craft what looks like such a straight-forward innovation. “The pieces were there, but nobody put them together,” he says. “And they were not obvious to put together.”