With apologies to everyone’s favorite autumnal fruit, scientists Beelee Chua and Donghyun Lee have demonstrated why we may need to change the phrase to “a chocolate a day keeps the doctor away.”
In new research published in ACS Applied Materials & Interfaces, the scientists from Korea University turned Tootsie Roll candy into a salvia-based health sensor that can monitor ovulation status and kidney health.
Given power consumption needs, novel materials and a myriad of other high-performance indicators, medical diagnostics invented in developed countries are often incompatible in resource-limited areas. In these places, even single-use diagnostic tests aren’t practical for health professionals or patients due to costs and waste disposal.
Trying to come at the problem from a different angle, Chua and Lee asked: what is abundant no matter where you are, and can be inexpensively retrofitted into an accurate medical device? The unlikely answer: soft candy, or in this case a Tootsie Roll.
The researchers’ first step was to turn the Tootsie Roll into an electrode-liquid interface for salivary conductivity measurement. They flattened the Tootsie Roll and pressed crevices into its surface in a crosshatched pattern they hoped would hold and contain the saliva sample. Then, they inserted two thin, reusable aluminum tubes that acted as electrical contacts, connecting the candy electrode into a circuit with a current source and an output voltage detector.
“The hallmark of a reliable electronic component is a stable frequency response across multiple runs and samples,” explained the scientists.
To demonstrate this, the duo used saline and artificial saliva to test both the frequency and temperature response of the candy electrode. The results showed sufficient overall conductivity, good output voltage, and only minor temperature fluctuations in line with the output voltage.
Importantly, these tests established a limit of detection of 1630 conductivity/centimeter (μS), which the researchers then used in preliminary tests for ovulation- and kidney disease-based diagnostics.
According to previous literature, the salivary conductivity of a healthy adult is about 3500 μS/cm. That number drops 10 to 30% for women in the days prior to ovulation—placing most women in the 2450 to 3150 μS/cm range.
“Given the limit of detection, the Tootsie Roll electrode will be able to measure saliva with decreased conductivity,” the researchers write in their study. “Furthermore, the soft candy electrode will definitely be able to differentiate saliva conductivities of 3500 and 2450 μS/cm (30% decrease), which means that even though it may not work for everyone, like all medical devices, there exists a definite segment of beneficiaries.”
Similarly, chronic kidney disease patients have been shown to have consistently high salivary conductivities of up to 13,000 μS/cm compared with healthy adults. Using extrapolated figures, the researchers confirmed the Tootsie Roll electrode could easily detect a chronic kidney problem, as well.
Although testing of the Tootsie Roll electrodes with real human samples is still needed, the researchers are optimistic, saying their findings open up the possibility for low-waste, inexpensive electrochemical sensors and circuits suited for use in resource-limited clinical settings.
“This study has ushered in an entirely new class of electronic materials and has elevated the perception of soft candy from an inconspicuous common confectionary to an edible, moldable, high-resistivity, and reliable electrical conductor with a stable electrode-liquid interface,” conclude the researchers. “With further appropriate modifications, future possibilities can include edible electrochemical sensors and biosensors, as well as edible circuits.”
Photo: An electrode made with a molded Tootsie Roll and aluminum tubes can help monitor ovulation status and kidney health. Credit: Adapted from ACS Applied Materials & Interfaces 2021, DOI: 10.1021/acsami.1c11306