Tattoo-like epidermal sensors are an emerging class of truly wearable electronics, owing to their thinness and softness. While most of them are based on thin metal films, a silicon membrane, or nanoparticle-based printable inks, we report sub-micrometer thick, multimodal electronic tattoo sensors that are made of graphene. The graphene electronic tattoo (GET) is designed as filamentary serpentines and fabricated by a cost- and time-effective "wet transfer, dry patterning" method. It has a total thickness of 463 ± 30 nm, an optical transparency of ∼85%, and a stretchability of more than 40%. The GET can be directly laminated on human skin just like a temporary tattoo and can fully conform to the microscopic morphology of the surface of skin via just van der Waals forces. The open-mesh structure of the GET makes it breathable and its stiffness negligible. A bare GET is able to stay attached to skin for several hours without fracture or delamination. With liquid bandage coverage, a GET may stay functional on the skin for up to several days. As a dry electrode, GET-skin interface impedance is on par with medically used silver/silver-chloride (Ag/AgCl) gel electrodes, while offering superior comfort, mobility, and reliability. GET has been successfully applied to measure electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), skin temperature, and skin hydration.

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Carbon nanotubes (CNTs) are a rapidly maturing emerging technology for next‐generation energy‐efficient digital Very‐Large‐Scale‐Integrated (VLSI) systems. However, a major remaining challenge facing CNT field‐effect transistors (CNFETs) are metallic CNTs, causing incorrect logic functionality and increased leakage power. As no CNT synthesis technique demonstrates a reliable path toward manufacturing 99.99% semiconducting CNTs (s‐CNT; required purity for VLSI systems), significant work focuses on solution‐based sorting of CNTs (selectively removing metallic CNTs post‐synthesis). Yet, there lacks both well‐controlled comparisons carefully optimizing key processing parameters simultaneously (CNT synthesis sources, polymer additive used for selective sorting, etc.), as well as statistically significant electrical transistor characterization sample sizes to form concrete conclusions. Here, >90 000 CNFETs (totaling >90 million CNTs) are fabricated and characterized to demonstrate the following key advances: 1) systematic exploration of the impact of different combinations of CNT synthesis sources and polymer additives on the electrical performance of transistors (analyzing on‐current, off‐current, on off ratio, and threshold voltage) to find the best combination, 2) how the optimization and choice of the CNT source can be decoupled from that of the polymer, and 3) an optimal CNT solution that achieves >99.99% s‐CNT purity using electrical measurements, meeting the requirement for VLSI systems.