According to Italian research, copper phthalocyanine (CuPc), a common tooth-whitening agent, also works in nano transistors, and could open the door to safe and reliable edible electronics.
They discovered that the amount of the material humans are already ingesting through routine dental hygiene was sufficient to construct a transistor. The team works for Milan’s Istituto Italiano di Tecnologia (IIT-Italian Institute of Technology), an organization with a history of pursuing advances in edible electronics.
Edible Electronics
With continuing advances in medical technology, safely getting devices inside the human body is one of the primary focus points. Surgeries are costly and come with a risk of complications. The team at ITT has been working on edible electronics to improve accessibility. Their goal is to create biomedical sensors that can be safely ingested without supervision, alleviating some of the burgeoning workload placed on healthcare workers.
To achieve this, they began looking at what ingestible substances can also double as semiconductors. Their approach to the search was unconventional. Instead of looking at materials already approved for intentional human consumption, they looked at additives that are unintentionally swallowed without incident as a by-product of other applications, such as toothpaste and lipstick dyes. It was in this space that they discovered copper phthalocyanine.
From Whitener to Power Source
Copper phthalocyanine is a synthetic crystal most commonly used as a blue dye, a common toothpaste ingredient for about 15 years. When added to toothpaste paste, it sticks to the enamel, creating a whiter appearance. The team began their two-phase research by assessing whether the amount needed to develop functional transistors would be safe or lead to toxicity in the human body. Throughout the day, the substance falls off of the teeth. By analyzing various clinical data and laboratory tests, they concluded that it amounts to an average person swallowing roughly half a milligram of CuPc daily.
It turned out that this was plenty of the substance to make many transistors. “With the amount of copper phthalocyanine we ingest daily, we could theoretically manufacture approximately 10,000 edible transistors,” reported lead author Elena Feltr. The study identified “molecular planarity, good air stability, and a demonstrated field-effect charge carrier mobility” among some of the most promising attributes of CuPc for their intended application. Additionally, its low solubility in bodily fluids like saliva makes CuPc-based transistors especially suited to oral delivery.
Producing the Edible Transistor
Their innovation involved pairing this new semiconductor with an existing circuit fabrication method. An ethylcellulose substrate forms the base of the circuit. Then, a CuPC film is evaporated onto the substrate, and an inkjet prints food-grade gold electrical contacts onto it. Another common food additive, chitosan, a gelling agent, is used as a gate to allow low-voltage functionality below 1V. Test results indicated that the transistor should have stable functionality for over a year when exposed to air and be capable of two orders of magnitude of current modulation.
The lab where the research occurred, run by Mario Caironi, has a history in edible technology. Last year, he led a project that involved designing an edible battery. They plan to continue researching this frontier, including working on the European RoboFood project. The next step for CuPC-based transistors will be tuning the edible substrate to better control the growth of CuPc crystals. Beyond that, they seek to identify other substances suitable for constructing electronics that can operate inside the human body.
The paper “A Fully Edible Transistor Based on a Toothpaste Pigment” was published in Advanced Science on September 16, 2024.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.