Graphene electronic tattoos 2.0 with enhanced performance, breathability and robustness

Abstract Graphene electronic tattoos (GETs) have recently emerged as unique tools for personalized healthcare. The monolayer GETs have been used to monitor human electrophysiological signals, including brain, heart, and muscle activities, skin temperature, and hydration level. However, a few drawbacks of the earlier GETs hindered their perception by clinical and biomedical experts: they were not permeable to sweat, and the tattoo performance varied greatly. In this work, we introduce GETs 2.0: the skin wearable tattoo sensors with superior electrical properties, permeability to sweat, and robustness. We report on the categorical analysis of the graphene tattoos of different layer constitutions. When stacking the graphene monolayers within a single tattoo, we see a drastic enhancement in their electronic properties. The older monolayer GETs were susceptive to minor growth- or transfer-related discrepancies, resulting in highly scattered electrical properties. In this work, the GETs 2.0 with the addition of graphene nanoscrolls (GNS) or multilayer (2 L and 3 L) graphene structures exhibit 3.5-fold decreased sheet resistance, 2.5-fold lower skin impedance, and 5-fold reduced standard deviations of these values. In addition, we introduced holes into the tattoo, enabling healthy sweat evaporation without a substantial decrease in electrical properties. Furthermore, we show that microholes allow for advanced biplanar contact with graphene tattoos. Finally, we show that multilayer GETs 2.0 can be used as efficient skin-wearable electronic heaters, exhibiting heating efficiency of ~6 mW/°C.