Miniaturizing microelectronic sensor technology, microelectronic robots, or intravascular implants is quickly advancing, but it also presents challenges for research. The largest roadblock is building miniscule but efficient energy storage devices that can enable operation of microsystems that work autonomously and in more and tinier areas of the human body. These energy storage devices must also be biocompatible, naturally.

A breakthrough prototype of this nature was developed by an international research team led by Prof. Dr. Oliver G. Schmidt, Professorship of Materials Systems for Nanoelectronics at Chemnitz University of Technology, initiator of the Center for Materials, Architectures and Integration of Nanomembranes (MAIN) at Chemnitz University of Technology, and director at the Leibniz Institute for Solid State and Materials Research (IFW) Dresden. The researchers also reported on the microsupercapacitors they developed—claimed to be the smallest to date—in the current issue of Nature Communication.

The microsupercapacitors already functioned in artificial blood vessels and can be used as a source of energy for a tiny pH sensor system. The storage device opens the potential for intravascular implants and microrobotic systems for next-generation biomedicine that could travel to hard-to-reach small spaces deep inside the body.

“It is extremely encouraging to see how new, extremely flexible, and adaptive microelectronics is making it into the miniaturized world of biological systems,” Prof. Dr. Schmidt told the press.

“The architecture of our nano-bio supercapacitors offers the first potential solution to one of the biggest challenges—tiny integrated energy storage devices that enable the self-sufficient operation of multifunctional microsystems,” added Dr. Vineeth Kumar, researcher on Prof. Dr. Schmidt’s team and a research associate at the MAIN research center at Chemitz.

Currently, the smallest “nanobiosupercapacitors” (nBSC) are larger than 3 mm3. Schmidt’s team was able to achieve a 3,000 times smaller tubular nBSC, with a volume of 0.001 mm3 (or 1 nanoliter). It takes up less space than a grain of dust, yet is able to deliver up to 1.6 V of supply voltage for microelectronic sensors. Its power level is approximately equal to the voltage of a standard AAA battery, and flexible tubular geometry allows self-protection against deformations caused by pulsating blood or muscle contraction. At full capacity, it can power a complex fully integrated sensor system to measure blood pH.

The pH of blood is subject to fluctuations, and continuous pH measurement can help in early detection of tumors. Because of this, the researchers built a pH sensor that can be powered by the nanobiosupercapacitor. The team used a nBSC-based ring oscillator for the project. A pH-sensitive BSC was integrated into the ring oscillator for a change in output frequency depending on the electrolyte’s pH. The pH-sensitive ring oscillator was also formed into a tubular 3D geometry using the “Swiss-roll” Origami technique—resulting in a fully integrated and ultra-compact system of energy storage and sensor.

This micro sensor system’s hollow inner core serves as a channel for the blood plasma. There are also three nBSCs connected in series with the sensor that enable efficient and self-sufficient measurement of pH. The researchers believe these properties open a wide range of possible applications in diagnostics and medicine.