Ultrafast optical reduction of graphene oxide sheets on colorless polyimide film for wearable chemical sensors

Optically reduced graphene oxide (RGO) sheets were produced on a thermally stable and highly transparent colorless polyimide (CPI) substrate by irradiating intense pulsed light (IPL) on a GO-coated CPI film. These RGO sheets can be used as flexible gas sensing layers for wearable applications. Ultrafast IPL irradiation formed RGO sheets on the CPI film within 4 msec without any damage on the plastic substrate. The IPL-induced RGO (IPL-RGO) sheets exhibited dramatically improved chemical sensing performance toward H2S, C2H5OH, and H2, while the pristine GO sheets did not show any gas responses. In addition, consistent sensing properties were maintained even after the IPL-RGO sheets on the CPI film were mechanically deformed for 104 bending cycles. The gas responses of an IPL-RGO sensor toward H2S, C2H5OH and H2 were clearly distinguished by pattern recognition based on principal component analysis. Moreover, we successfully integrated our IPL-RGO sensor on a flexible printed circuit board with wireless Bluetooth communication and demonstrated outstanding sensing properties for potential applications in environmental and healthcare monitoring. A bendable, Bluetooth-connected device that senses environmental gases can be fabricated in just milliseconds using intense laser light. The rigid silicon substrates used to construct most chemical gas sensors pose problems for applications such as wearable environmental monitors. Il-Doo Kim and colleagues from the Korea Advanced Institute of Science and Technology have now developed an alternative gas-sensing platform based on graphene oxide sheets and transparent, flexible polymers. The team synthesized a colorless polyimide film with high thermal stability, coated it with graphene oxide, and then used short bursts of broad-spectrum laser light to transform the graphene oxide sheets into a reduced graphene oxide sheets sensitive to gases such as ethanol, hydrogen, and hydrogen sulfide. Integration into a wireless, watch-type device revealed the gas sensor retained high sensitivity after more than 10,000 bending cycles. Ultrafast reduction of graphene oxide sheets was achieved by intense pulsed light irradiation on a highly transparent and thermally stable polyimide substrate. The obtained reduced graphene sheets exhibited improved chemical sensing characteristics, which are promising in wearable chemical sensors for real-time environmental monitoring.