16th NANOSCIENCE & NANOTECHNOLOGY CONFERENCE, Ankara, Turkey, 5 - 08 September 2022, pp.214
In today's world, where global commerce and information technologies are rapidly developing, the economic losses caused by counterfeit goods, currency, or identity, as well as the health and safety risks associated with counterfeiting cannot be underestimated. Conventionally used cryptographic primitives are clonable due to their deterministic fabrication processes as well as predictable encoding and decoding mechanisms. A promising solution that has gained recent attention involves the exploitation of physically unclonable functions (PUFs)[1,2]. In this approach, the response of the encoded surface against a challenge is determined through a physical and stochastic process. This stochasticity and inherently random responses against challenges prevent the replication of encoded surfaces by third parties or even by the manufacturer itself. However, simultaneously meeting the requirements of an ideal PUF including low-cost fabrication, versatility, practical coding- decoding-and-authentication, and high-level security with multi-layered security easures is still challenging. Herein we present a novel strategy for integrating all the benefits of low-cost fabrication, easy authentication, and multi-layered high-level security into a PUF system via electrospraying technique. The approach called "E-spray PUFs" has many peculiarities. The key advantage of this strategy is that electrohydrodynamic instabilities esulting from the chaotic interaction of different intertwined forces that occur during the process offer a very useful way to generate random complex features. It has been shown that nanoscopic, microscopic, and/or nanostructured features are obtained effectively and in a controlled manner by simply adjusting the electrospraying parameters. Besides the andomness in the spatial positions and sizes of the features, another enabling characteristic of the presented approach is the ability to generate complex 3D shapes, which are very challenging to fabricate with the most advanced fabrication techniques. E-spray PUFs obtained by using a wide range of polymers have very high encoding capacity and near-ideal figure of merits (randomness, uniformity, reliability, etc) values. Thanks to the solution-based and additive operation nature of the process, it enables polymeric structures unctionalized with multiple materials to be sequentially electrosprayed on the same substrate. In this way, fluorescence molecules with distinct photophysical properties, quantum dots emitting at specific wavelengths or metallic nanoparticles with plasmonic properties can be directly cooperated into the features or site-specificly immobilized on the surface of he features. The resulting multiplexed PUFs can be authenticated at different levels, which can be performed independently. Extra coding layers are established with coherent aspects such as spatial random positions and complex morphologies on the surface of sequentially deposited structures, photophysical behavior of functional materials in the tructure, structural colors, specific wavelengths, surface-enhanced plasmon properties, etc. In addition to the direct application of PUFs on the label of goods, practical and precise authentication approaches of these PUFs are also presented The authentication steps of optical responses are effectively performed using ORB algorithm without the need for arkers and precisely defined rotation angles, greatly relaxing constraints associated with the imaging. Finally, authentication via compact microscopes demonstrates the practical tility of the presented strategy.