Concealable Physically Unclonable Functions via Wetting-Driven Tunable Opacity in Smart Nanofibrous Mats.

The concealing of uniquely identifiable information is pertinent to both anti-counterfeiting and information security technologies. Current optical physically unclonable functions (PUFs) are based on static stochastic features that make them inherently vulnerable to undesired tampering. This study proposes wetting induced transparency variations in a smart material platform consisting of a stimulus-responsive nanofibrous layer doped with quantum dots (QDs). The platform combines two forms of electrohydrodynamic instabilities through the deposition of QDs via electrospraying, and generation of entangled nanofibers of polyacrylonitrile via electrospinning. Upon wetting, the contrast of the refractive indices is temporarily reduced, which decreases scattering and allows access to the underlying fluorescent QD features. After the solvent has evaporated, the mat returns to its opaque, scattering state and again conceals the PUF response. When the image is captured, it becomes a 256-bit cryptographic key of high uniformity, uniqueness, and randomness. The stochastic QD distribution and nanofiber architecture concealement together ensure strong, physically unclonable optical fingerprints. By confining the readout to a controlled physical condition that arises only during wetting, the platform adds a concealment-based security dimension in which the revealed features can be reproducibly read while remaining inaccessible under ambient conditions.