Ultraflexible tattoo electrodes for epidermal and in vivo electrophysiological recording

Tattoo electronics, flexible patches that mount directly onto the skin with the ease and flexibility of a temporary tattoo, have foreseen remarkable application potentials in personalized healthcare moni-toring and human-machine interfaces. Documented tattoo elec-tronics mostly have an on-skin form factor to date. Using dermal tattoos for in vivo diagnostics presents an unexplored paradigm. Here, we extend the application scenario of "tattoo electrodes"from an on-skin fashion to an actual under-skin configuration, enabled by a highly soft, conductive, and biocompatible polymer matrix. With printed ultrathin electrodes, we achieve a record -high conductivity and record-low skin contact impedance, allowing the design of a single-lead electrocardiogram system for seamless wearing and precise detection of intervals and rhythms in dynamic conditions. Furthermore, the biocompatible ink enables the devel-opment of dermal electrodes by virtue of tattoo artistry. It shows enormous potential for electrical communication between bio-electronics and biological tissues at a deep-tissue level.