Ultrathin Nanocrystal-Based Resistive Skin Conforming to Finger Knuckle Wrinkles for Dynamic, Nontransferable Wearable Authentication.

With the rapid expansion of the Internet of Things (IoT), secure authentication has become paramount for safeguarding the digital ecosystem against spoofing attacks and privacy breaches. Optical and acoustic modalities currently dominate biometric authentication; however, they remain inherently vulnerable to environmental interference. Here, we report ultrathin (<50 nm), substrate-free gold nanoplatelet skins that conform intimately to finger-knuckle wrinkles, enabling dynamic and nontransferable wearable authentication. Unlike light- or sound-based systems, these nanocrystal skins generate unique resistive signatures that are insensitive to optical and acoustic perturbations. Fabricated from additive-free, polystyrene-capped gold nanoplatelets, the conformal films establish gapless skin-electronic interfaces that replicate knuckle microtopography with high fidelity. This intimate coupling is the key to converting bending-release motions into finger-specific electrical signatures that are unattainable with the corresponding substrate-supported, nonconformal system. Integrated with a deep-learning framework, the two-finger nanoplatelet skin achieves near-perfect authentication accuracy. Our findings indicate that substrate-free nanocrystal skins could enable next-generation wearable biometric authentication, advancing hardware-level security for the digital world.