As nature's catalysts, enzymes facilitate many essential chemical reactions in living organisms, ranging from food digestion to DNA repair. Their ability to recognise specific biological targets and boost reactions makes them a valuable component for wearable health devices.
“Enzymes themselves are not consumed in the catalysis process, [and are] hence suitable for use as biosensors,” said Le Yang, a Principal Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE). These properties enable them to help measure metabolites in the body precisely and in real time, providing vital health insights.
For instance, glucose oxidase enzymes used in continuous glucose monitors allow people with diabetes to track their blood sugar levels without the need for finger-prick blood tests, alerting them to highs and lows. Meanwhile, wearable lactate sensors—which employ lactate oxidase enzymes—enable athletes to monitor their training intensity and recovery.
However, such enzymes are notoriously unstable outside optimal conditions, often deforming under ambient temperatures or when exposed to static electricity. This instability reduces the lifespans and limits the effectiveness of enzyme-based biosensors.
To tackle this issue, Yang led a research team in designing a protective 'cage' to shield these sensitive enzymes from the harsh environments often found within electronic devices. The team's approach involved co-encapsulating enzymes with arginine-derived carbon dots within a metal-organic framework (MOF), enhancing both the stability and electrochemical sensitivity of the enzymes contained.
The team found it challenging to balance enzyme protection with functionality. "The extremely tiny pores of conventional microporous MOF frameworks hinder analytes from accessing enzymes, decreasing their sensitivity," said Yang.
In response, Yang and colleagues developed a novel composite MOF that incorporates carbon nanodots with enzymes, featuring larger pore sizes that allow metabolites better access. The new hybrid enzyme-carbon dot composites showed a 40 percent increase in electrochemical sensitivity versus traditional approaches, along with significant stability improvements.
Impressively, the novel composites also maintained full catalytic activity and sensitivity over 30 days of testing, which was substantially longer than previous enzyme applications.
"These results are particularly exciting as they represent one of the first demonstrations of overcoming long-standing imbalances between biosensor stability, sensitivity and selectivity," said Yang, adding that the technology’s applications go beyond healthcare to any sensors or devices that need durable, efficient enzymes.
The team plans to expand their MOF platform to detect a broader range of substances, including uric acid, creatinine and cholesterol, and to further optimise hybrid composites for improved sensor performance. They also aim to develop wearable integrated prototypes that incorporate these advanced composites into non-invasive, real-time and multiplexed electrochemical biosensors.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).
