Semiconducting and environmentally responsive melanin-doped silk nanofibers for multifunctional electronic tattoos.

On-skin electronics are gaining attention in diagnostics and therapeutics due to their capabilities such as continuous real-time operation. Among them, ultrathin electronic tattoos (E-tattoos) offer the advantage of imperceptible operation, making them suitable for daily use. However, the insulating trait of polymeric materials used for skin adhesion and integration of electronics hinders electrical interfaces between electronics and skin. This study investigates multifunctional E-tattoos by materializing semiconducting silk nanofibers (SNFs) with the melanin dopant. Fabricated through electrospinning and subsequent melanin doping and graphene coating, ultrathin and lightweight E-tattoos exhibited mechanical flexibility, strong skin conformability, and high water-vapour transmission, ensuring long-term on-skin usability. Their use as electrocardiogram electrodes and in skin hydration monitoring with a high signal-to-noise ratio is possible due to the increased conductivity of the melanin-doped SNFs. In addition, light- and humidity-responsive conductivity of melanin enables the use of E-tattoos as a breath sensor and UV detector. The unique combination of bio-based materials and advanced fabrication processes enables seamless integration of electronic and biological systems. The graphene/melanin-doped SNF E-tattoos for bio-signal sensing applications offer an eco-friendly, skin-compatible, and multifunctional solution for next-generation biomedical research.