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Thanks to the highly flexible and stretchable properties of organic semiconductors, a new class of smart sensors based on organic field effect transistor (OFETs) have been developed. Different from the inorganic counterparts, the organic semiconductors do not require high processing temperature and substrates with matched lattice constant. Such properties allow them to bring a revolution to the manufacturing of electronics by making those devices on polymer substrates through extremely low cost row-to-row fabrication. Recently, our research team has successfully fabricated varies kind of health monitoring sensors including temperature, pulse and glucose sensors based on OFETs and similar structure. The success of these wearable sensors are expected to serve as the first guardian on our health and allow us to have immediate care.

In the temperature sensor devices, they are majorly different from the traditional individual devices from the active matrix configuration, which is critical and essential for two dimensional information mapping. The 16´16 temperature sensors have a temperature resolution of 0.2K and able to map out the temperature information of the object surface (Figure 1). Our devices also allow a higher spatial resolution then the passive matrix form as common electrodes are used in the whole array. Other than thermal mapping for the electronic components, our devices can also be applied onto human skin or even organs. A very recent study has point out that the temperature of blood vessel would drop for more than 5 degrees Celsius while a subject is performing numerical calculation. Such kind of body temperature mapping can be an important indicator to let us understand more about how would our body response to external stimulations.

Other than temperature, the radial pulse also consists a lot of important information in our body. To develop the flexible pulse sensor, we utilized micrometer scale micro-hump structures to enhance the sensitivity of the device and make it suitable for the radial pulse sensing. One of the most important information we can extract from the radial pulse is cardiovascular conditions, which can be evaluated by the augmentation index (AI) of the subject. Real-time monitoring of the AI would allow us to provide timely response to the patients and minimize their chances of having a stroke. The images shown in Figure 2 are the electrical signal obtained from our radial pulse sensor attached on the wrist of a normal female subject and a pregnant subject where a clear difference in the radial signal can be observed. The calculation formula of the AP is also listed in figure 2.

The last smart sensor we demonstrated is the glucose sensor which has a sensitivity down to 10-7 M.  Such high sensitivity is important as it implies glucose sensing through saliva is feasible since the human glucose concentration is around 10-5 M or higher and the traditional invasive blood test can be replaced. The high sensitivity is majorly achieved by the high catalyst property of special treated platinum nanoparticles, and the transistor structure can also be used to magnify the sensed signal. This method can avoid the chances of the patient being infected by bacteria during the invasive blood test. More importantly, we further also develop a Android APP for the glucose sensor to perform data logging and real time monitoring of the subject. The data can be easily transfer to the medical doctors anytime for timely responses. Based on this device and concept, a startup company is further supported by the TSSSU program for the device development purposes.

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Related publications (Underline – HKU researchers, *– corresponding author):

X. C. Ren, K. Pei, B. Y. Peng, Z. C. Zhang, Z. R. Wang, X. Y. Wang, and P. K. L. Chan*, “Low operating power and flexible active matrix organic transistor temperature sensors array”, Adv. Mater., DOI: 10.1002/adma.201600040, 2016.

Z. R. Wang, J. F. Zeng, X. C. Ren, A. J. Y. Chee, B. Y. S. Yiu, W. C. Chung, Y. Yang, A. C. H. Yu, A. C. O. Tsang, K.W. Chow and P. K. L. Chan*, “Fast response, high sensitivity flexible piezoresistive pressure sensor for human blood flow monitoring”, Small., smll.201601419, 2016.

X. D. Ji, H. Y. Lau, X. C. Ren, B. Y. Peng, T. S. P. Feng and P. K. L. Chan*, “Highly Sensitive Metabolite Biosensor Based on Organic Electrochemical Transistor Integrated with Microfluidic Channel and Poly(N-vinyl-2-pyrrolidone)-Capped Platinum Nanoparticles”, Adv. Mater. Tech., DOI: 10.1002/admt.201600042, 2016.

Knowledge exchange activities:

A start up company is funded by The Innovation and Technology Commission (ITC) through the Technology Start-up Support Scheme for Universities (TSSSU) scheme.