Since the start of the 2020s, the COVID-19 pandemic has forced us to change our lifestyles dramatically. At present, traditional human activities have become things of the past, and we have again realized that our social lives are like a house of cards, ready to topple at the slightest disturbance.

To continue a healthy life amidst the spread of serious infectious diseases or under a mental stress, it is effective to monitor the physiological conditions of our own bodies. Toward this end, while many types of wearable sensing platform have been demonstrated, the specific and quantitative detection of biomarkers utilizing ultraflexible devices has not yet been established. The development of wearable sensing platforms for the measurement of chemical information in organisms remains in its infancy, notwithstanding a long history of biosensors of over a half-century since the 1960s. We considered this might be attributed to the fact that cooperation between molecular recognition chemists and device engineers has been insufficient. To obtain accurate and reproducible signals of protein recognition on electrical devices, suitable designs of sensing portions should be developed. Nevertheless, such designs have not been considered in the field of device engineering. In contrast, although the need for such designs has already been demonstrated by molecular recognition chemists, the preparation of suitable ultraflexible devices remains in its early stage. 

In this research, we successfully fabricated an ultraflexible biosensor that can respond electrically to changes in the levels of an immunological marker protein by considering simultaneously these different viewpoints. To demonstrate the feasibility of organic thin-film transistors (OTFTs) as wearable sensing platforms, we developed a printed ultraflexible device for the accurate and reproducible detection of a biomarker on the basis of molecular recognition chemistry. The abovementioned innovative immunosensor based on OTFTs printed on an ultrathin film can be utilized as an imperceptible sensing system for direct monitoring of biomarker information. In addition, the prepared device exhibits sufficient performance and can be compressed by 15% without mechanical or electronic degradation. This is an important step toward wearable sensors on human skin. 

Figure. Photograph of the fabricated flexible OTFT-based biosensor. The scale bar indicates 1 cm.

Such a sensing platform will open the way to the achievement of rapid and simple diagnosis in various situations. Interestingly, the selected target (IgG) in this work is widely utilized as the biomarker for infectious diseases and inflammation. Furthermore, OTFTs can be easily integrated into information-transmitting systems. This means that big data of bioactive information can be accumulated by using OTFT-based wearable sensors. Hence, it is possible to compare and accumulate physiological information obtained from each person. These ideas suggest that the designed flexible biosensor could contribute to realizing a more effective tool for maintaining healthy and full lives owing to its capability to sense macromolecular biomarkers such as antibodies and viruses.

For more information, please see our recent publication in Communications Materials: Flexible organic thin-film transistor immunosensor printed on a one-micron-thick film.