Disposable and biodegradable ultraviolet photodetector. (Credit: OEA)

Sensor-laden wearable systems hold great promise for wide range of applications including health monitoring, rehabilitation, electronic skin in robotics, environmental monitoring, Internet of Things (IoT), and more. Often these applications require cost-effective disposable sensors either for short-term or single measurements.

Single-use sensors in wearables could also help overcome the typical challenges related to washability. Likewise, disposable sensors could help address the hygiene requirements in health monitoring applications. Motivated by these requirements, Prof. Abhishek Singh Dahiya and his team present ZnO nano-wire-based high-performance ultraviolet (UV) photodetectors on flexible, biodegradable substrate.

The wearable, disposable device can accurately measure the UV light intensity. The sensing (ZnO nanowires) and substrate (chitosan) materials were selected to allow the device to harmlessly degrade in water during washing of sensors-integrated clothes. The use of chitosan as the substrate offers excellent chemical stability, good optical transparency, greater mechanical flexibility, and excellent biodegradability. Similarly, the ZnO nanowires offer distinct advantages, such as cost-effective synthesis, highly sensitive to UV light, environmental friendliness, biocompatibility, and biodegradability.

Further, the fabrication steps used for disposable sensors are eco-friendly, scalable, and resource efficient. These include facile synthesis of chitosan-based green substrates, spray coating of ZnO nano-wires, and screen printing to realize contact electrodes. Thus, both during the development and the end of life of sensors, negligible electronic waste (e-waste) is generated.

The Bendable Electronics and Sensing Technologies (BEST) research group, led by Prof. Ravinder Dahiya presents eco-friendly materials and a resource-efficient fabrication route to develop wearable UV dosimeters, which can be safely disposed of after their use and thus cause no adverse impact on the environment. Uncontrolled exposure to UV radiation is a major cause for skin cancer. The excess exposure could also damage the DNA of genes and hence the skin cell growth.

The amount of UV radiation reaching on earth surface varies from region to region. The seasonal UV intensity fluctuations, radiation leaks, and diverse geographical locations make UV detection quite challenging. Significant research efforts have been made for the development of portable UV sensors, with novel form factors including flexible and/or stretchable. Accordingly, many wearable and disposable consumer UV sensors have already been developed and are available in the market. However, disposability does not necessarily mean biodegradability, and this is where many of the reported devices fall short of expectations and do not fully address the growing issue of e-waste. These high-performance disposable, wearable photodetectors have no adverse environmental impact during their fabrication as well as after the end of life.

The eco-friendly set of materials is used to develop transient UV sensors that physically disappear after their use. The use of sustainable materials and zero or low-waste fabrication processes in this work would trigger further research on transient electronics and help reduce the adverse environmental impact of electronics.

The high-performance, conformal, and disposable photodetectors monitor exposure to UV radiation, which is considered as one of the main risk factors for developing nonmelanoma and melanoma skin cancers. Further, the device could be integrated over nonplanar surfaces such as clothes or skin for wearable dosimetry. Such wearable and disposable patches can be used for real-time monitoring of UV radiation under diverse environmental conditions.

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