Paper electronics are expected to be a game-changer in next-generation flexible electronics that could replace conventional plastic electronics. Paper electronics are disposable and cost-effective, two distinct advantages for the development of broadly accessible devices, but their poor performance has limited their practical implementation so far. Here, a high-sensitivity, high-performance, paper-based, wearable ammonia sensor comprising composite poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and iron(III) compounds is reported. The sensor achieves 10-times smaller size than the conventional sensor on Kapton film and high tolerance for humidity without losing practical sensor response. The utility of the device is demonstrated for wearable ammonia sensing in a facial mask and a nasal filter; wireless monitoring of food spoilage; and wireless monitoring of the ammonia level in a diaper. The approach of this study may open the door to advanced healthcare based on ubiquitous wearable sensing.
The rapid detection of postprandial hyperglycaemia (PPHG) is imperative for the diagnosis of diabetes and the assessment of health risks for nondiabetics. Battery-free flexible glucose sensors are a promising tool for glucose sensing with a relatively low burden on biological tissues and living bodies because they are more lightweight and flexible than conventional battery-driven glucose sensors. However, existing battery-free glucose sensors are unsuitable for the practical detection of hyperglycaemia because of their long response time (>1 h) and response fluctuation. In this research, we demonstrated a unique combination of materials and device design—phenylboronic acid (PBA) hydrogel integrated with an inkjet-printed interdigitated capacitor (IDC)—that enabled rapid response to the change in the glucose concentration. In particular, the following three essential capabilities have been demonstrated: (1) quick response time (<5 min) to mouse serum under hyperglycaemia in a battery-free setting, (2) conformability of soft PBA hydrogel suitable for use on biological surfaces, and (3) controlled design of the signal transducer enabled by digital fabrication. We believe that these capabilities serve as core technologies toward the development of tissue-interfaced battery-free glucose sensors with improved response time.
Local delivery of physical energy, such as heat, is promising for the treatment of target lesions without the unintended distribution of heat to other normal tissue. However, the heating device must be equipped with an external power source or strong magnetic field to operate the device, and many of them are too large to be placed inside the body. In this regard, wireless, lightweight, flexible electronics can be used for the miniaturization of implantable devices. In this study, a flexible induction heating (IH) device is reported that integrates inkjet-printed wirings and flexible polymeric thin films, specifically Au nanoink-based wirings (thickness: 1.5 µm) and a biodegradable poly(D, L-lactic acid) (PDLLA) thin film (thickness: 5 µm). A unique method of transferring the inkjet-printed Au nanoink wiring onto the PDLLA thin film realizes the integration of the following technical features in one device: biocompatible packaging, a printed IH system, and body conformability. The resulting thin-film IH device is successfully placed on a hepatic lobe of a beagle dog, which allows for a local increase in temperature of 7 °C after 1-min power feeding without tissue inflammation. The thin-film IH device is expected to provide minimally invasive thermotherapy when combined with endoscopic surgery.
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