Single-Step Enzyme Ink Enables Mass-Producible, Self-Powered Wearable Biosensors

Wearable biosensors that analyze sweat in real time hold considerable promise for continuous health monitoring - tracking lactate during exercise, glucose for metabolic assessment, and other biomarkers without requiring blood draws or clinic visits. The technology exists in principle. The obstacle has been manufacturing.

Building a sensor that generates its own power from the chemicals in sweat requires an enzymatic biofuel cell - a device that uses enzymes as catalysts to convert glucose and lactate directly into electrical current. Assembling one currently involves printing a carbon electrode layer, then separately depositing enzyme and mediator solutions onto the surface, then drying the assembly. Each step introduces variability. The resulting devices are difficult to standardize, expensive to produce at scale, and ill-suited to the demands of consumer electronics manufacturing.

A team led by Associate Professor Isao Shitanda from the Department of Pure and Applied Chemistry at Tokyo University of Science in Japan has developed a potential solution: water-based enzyme inks that consolidate all components into a single printable formulation. Their findings, published in ACS Applied Engineering Materials on February 6, 2026, demonstrate that fully functional enzymatic biofuel cells can be produced in one printing step, with performance comparable to conventionally assembled devices.

What Goes Into an Enzyme Ink

The ink combines four components that previously required separate deposition steps: enzymes that catalyze the oxidation of glucose or lactate, electron mediators that shuttle electrons from the enzyme reaction to the electrode surface, carbon materials that form a conductive matrix, and binders that hold the mixture together during and after printing.

Mixing these components has been attempted before. The challenge is stability. Enzymes are fragile proteins that lose activity when exposed to solvents, elevated temperatures, or incompatible materials. Previous attempts to combine enzymes with mediators and carbon materials produced inks that degraded quickly or printed unevenly. The Tokyo University of Science team addressed this by using a water-based formulation with carefully selected mediators - compounds that preserve enzymatic activity while remaining compatible with screen printing processes.

The resulting inks produced electrodes with uniform surface coverage and consistent enzymatic activity across multiple printed devices - a key requirement for any mass-production pathway.

Performance in Simulated Sweat

The team tested the printed biofuel cells against artificial sweat solutions at concentrations relevant to real physiological conditions. The anode, which uses lactate oxidase to harvest electrons from lactate, and the cathode, which uses bilirubin oxidase to reduce oxygen, together produced sufficient current to power a small sensor circuit without an external battery.

Critically, the power output was stable across multiple tests, suggesting the enzyme activity was preserved through the printing process. The team also demonstrated that the inks could be printed onto flexible substrates suitable for skin contact, a prerequisite for wearable applications.

"In order to avoid labor-intensive, inefficient, and expensive EBFC fabrication techniques, we need to bring an enzyme ink to the market that can be printed uniformly and is suitable for mass production," said Dr. Shitanda, describing the motivation for the work.

The Path to Consumer Wearables

Self-powered biosensors address a fundamental limitation of current wearable health devices: battery dependency. Devices that need external power sources are constrained by battery size, weight, and charging requirements. A sensor that generates electricity from the chemicals in sweat can operate continuously without these constraints, as long as the wearer is producing sweat.

Lactate, in particular, is a valuable metabolic indicator. It rises during intense physical activity, can signal tissue oxygen stress in clinical settings, and varies in predictable ways with exercise intensity. A wearable lactate sensor that does not require a battery would be valuable for athletic performance monitoring, physical therapy, and potentially for clinical applications in patients with conditions that affect tissue oxygenation.

The study represents early-stage work, and several steps remain before commercial deployment. The inks were tested in laboratory conditions with artificial sweat; performance in real sweat, with its variable pH, temperature, and ion composition, may differ. Long-term stability - how the enzyme activity holds up over weeks of use - has not yet been reported. The team also notes that scaling up ink production while maintaining consistency will require additional process development.

The co-first author on the research was Mahiro Omori, a first-year Master's student at Tokyo University of Science, alongside Mitsuru Hanasaki from RESONAC Co. Ltd., Japan - a collaboration that suggests industry interest in moving the technology toward practical application.

The broader opportunity is significant. The global wearable medical device market is growing rapidly, and the ability to print functional, self-powered sensors at scale using standard manufacturing equipment would remove a major cost and complexity barrier from the field.