According to scientists at the University of Southern California (USC), overuse of acetaminophen is the leading cause of acute liver failure in US children. It therefore stands to reason that infants, whose livers are less developed than those of older children, are even more susceptible to the ill effects of the drug.

Because acetaminophen is often prescribed to mothers who are experiencing pain after giving birth, it's inevitable that some of the medication will make its way through to the infant in the breast milk.

Typical concentrations are generally considered to be safe, although mothers taking higher doses can get their milk tested at labs in order to be sure. Lab tests take time, however, and aren't practical for mothers living in remote or otherwise resource-limited locations.

That's where the new USC-developed pad comes in.

Lactation pads are something that are already worn by most mothers in First World countries, in order to soak up the milk that leaks out of the breasts between feedings. In this case, however, the disposable pad contains paper-based microfluidic channels that draw milk from a ringed collection area on the skin-side of the pad, through to a sensor unit on the outside.

Utilizing LIG (laser-induced graphene) electrodes and an integrated flexible potentiostat, the sensor performs an electrochemical analysis of the milk, determining its acetaminophen levels. Those readings are wirelessly transmitted to an app on the mother's smartphone, which provides a real-time readout.

In a more basic alternate setup, a potentiostat-less version of the pad can simply be hardwired to a portable potentiostat for a one-time reading before being disposed of. That reading is still relayed to the app.

In either case, if the detected levels are dangerously high, the mother can opt to pump and discard the milk. She can then feed the infant earlier-pumped stored milk, or formula, until her acetaminophen levels are safe again.

"Our device represents a major innovation," says Asst. Prof. Maral Mousavi, first author of a paper on the study. "It is the first wearable tool for direct biochemical analysis in breast milk and the first lactation pad embedded with real-time sensing technology."