Consumables Edible transistors made from toothpaste

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An Italian research team has succeeded in producing functioning transistors from pigments of a whitener used in toothpaste. Such edible electronics, which harmlessly dissolve after use in the body, open up new possibilities in medical technology.

The more efficiently health data can be measured and monitored directly from patients, the better doctors can assess conditions and make timely interventions. However, challenges remain, such as introducing sensors into the body without surgery and safely removing them afterward. Innovative solutions include ingestible sensors, which are pill-sized devices that can collect data from the gastrointestinal tract and transmit it wirelessly to an external device for analysis. These sensors pass naturally through the body without requiring surgical extraction. Another promising technology is biodegradable electronics, which perform their functions in the body and dissolve naturally, eliminating the need for removal. Both approaches aim to reduce medical invasiveness and improve patient comfort.

The answer might indeed be found in toothpaste: A research team from the Istituto Italiano di Tecnologia (IIT) has developed edible transistors made from a material commonly found in the form of small blue pigments in toothpaste: copper phthalocyanine. This odorless solid deposits on the teeth and acts like an optical filter, making the teeth appear whiter. Throughout the day, copper phthalocyanine is gradually removed by saliva, ingested with food, and eventually broken down without residue. According to the researchers at IIT, we ingest about one milligram of this solid each time we brush our teeth. Additionally, copper phthalocyanine can also serve as a type of organic semiconductor since its crystalline structure possesses good electrical conductivity.

A printed nano-transistor that dissolves after a year

The research team at the Istituto Italiano di Tecnologia (IIT) has successfully developed a fully edible, electrolyte-gated transistor based on the whitening agent found in toothpaste. This easily reproducible integrated circuit can operate at a low voltage of less than one volt and maintain stable performance for more than a year. After its utility has been exhausted, the edible electronic component is completely broken down by the body without leaving any residue.

Very little material is required for this nanoelectronics: "With the amount of copper phthalocyanine we ingest daily, we could theoretically produce about 10,000 edible transistors," says Elena Feltri, lead author of the accompanying study and a doctoral candidate at the IIT Center for Nanoscience and Technology in Milan. A chip composed of 10,000 transistors would be on the performance level of an old 8-bit or a very early 16-bit processor, comparable, for example, to a Zilog Z80 CPU or a TMS9900.

As a substrate, an ethyl cellulose material is used, which is commonly employed in the pharmaceutical and food industries. The electrical connections on the circuits are printed using inkjet technology. In this instance, the ink contains a solution of gold particles, which serve as the electrical contacts and, being a noble metal, are harmless to the body in very small amounts.

In this way, a logic gate that regulates the flow of current can be printed for each transistor. This gate is made from chitosan, a natural polymer derived from the shells of crustaceans and often used in the food industry as a gelling agent. By applying a low voltage (less than 1 V) to the gate, the current flow through the transistor can be controlled, thus turning it on or off. Poly(chloro-p-xylene)-C, also known as Parylene C, serves as the coating material and a dielectric interlayer. It has a good barrier effect against stomach acid. This enables the transistor to function smoothly within the body for up to a year before it dissolves.

For the required power supply, IIT is also already working on a suitable edible solution. The development of the transistor took place in the same laboratory for printed and molecular electronics where an edible battery was produced in 2023. The researchers anticipate that this technology will prove to be a future key component in the development of "Smart Pills." Such an electronic tablet or pill could, for example, monitor the health status inside the patient or be used for quality control in the feed and food industry, before it completely degrades after fulfilling its purpose.

The research team has published its study on the transistors developed in this way in the journal "Advanced Science." The study itself was published under a Creative Commons BY-4.0 license and is freely accessible in Open Access here. (sg)