A flash of light from a smartphone and a brief beam from a laser pointer may soon be enough to expose a counterfeit product. Researchers at the Korea Advanced Institute of Science and Technology (KAIST), working with scientists at Sungkyunkwan University, have developed a physical security technology that creates microscopic “artificial fingerprints” from the random arrangement of nanoparticles. The patterns are invisible to the naked eye, exceptionally difficult to reproduce, and capable of generating two independent optical signatures when exposed to different forms of visible light. The approach could offer a practical new way to authenticate electronic devices, luxury goods, medicines, artworks, and other products without relying on specialized laboratory equipment.
The technology addresses a growing weakness in modern security. Digital authentication systems can be attacked through stolen credentials, malware, artificial intelligence-assisted fraud, and increasingly sophisticated cyber operations. At the same time, future quantum computers could threaten some of the mathematical foundations used by conventional cryptographic systems. For that reason, researchers have been exploring physical unclonable functions, or PUFs, which use tiny, naturally occurring differences created during manufacturing as a source of security information. Instead of storing a secret only in software, a PUF binds that secret to the physical structure of an object. Every manufactured unit becomes subtly different, much as every human fingerprint differs from every other.
The KAIST-led team created its PUF by allowing spherical colloidal particles, each measuring several hundred nanometers across, to assemble spontaneously at a water surface. Colloidal particles are small solid particles suspended in a liquid, and under carefully controlled conditions they can organize into larger structures through processes driven by surface forces, evaporation, and interactions between neighboring particles. Rather than producing one perfectly uniform crystal, the researchers formed a polycrystalline pattern made up of numerous small crystalline domains. Each domain has its own size, orientation, and local arrangement. Because these features emerge from microscopic fluctuations during self-assembly, no two samples develop exactly the same pattern, even when the same materials and processing conditions are used.
This randomness is central to the security of the system. A potential counterfeiter would need to reproduce the identity of a particular sample at the level of individual particle positions and orientations. That is already an extraordinarily demanding task, but the challenge extends further: the reproduction would also need to generate the same optical response under separate illumination conditions. The researchers describe the resulting object as a nanofingerprint, a physical signature created by the structure itself rather than by a digitally programmed code. Its complexity comes from the enormous number of possible arrangements that can arise within the nanoparticle assembly, while its usability comes from the fact that those arrangements interact with ordinary light in readily detectable ways.
Under illumination from a conventional source such as a smartphone flashlight, the nanopattern produces a distinctive combination of color, brightness, and reflection. The precise appearance depends on how the crystalline domains are distributed and how their surfaces interact with incoming visible light. Differences in particle spacing, orientation, and domain size alter the way light is reflected, scattered, and potentially diffracted across the sample. To an observer, the result can appear as a unique color-and-reflection pattern. A smartphone camera or even a visual comparison system could record this response and compare it with a reference registered when the product was first manufactured.
The second authentication channel is generated by a laser pointer. Laser light is highly directional and typically has a much narrower range of wavelengths than the broad illumination produced by a flashlight. When the laser strikes the nanoparticle structure, the microscopic arrangement scatters the beam in multiple directions. The resulting optical pattern carries information about the internal organization of the particles and crystalline domains. Because the laser response is physically different from the flashlight response, it supplies an independent layer of verification. A genuine item must therefore match two related but distinct signatures: its appearance under diffuse visible illumination and its laser-scattering pattern.
This dual-space authentication strategy is comparable to checking two biometric characteristics rather than relying on one. A conventional label might be copied visually, and a single optical signal might be imitated or manipulated. Reproducing both signatures would require copying the underlying nanostructure with exceptional precision, then reproducing its behavior under two different types of light. The researchers argue that this combination creates a strong barrier against counterfeiting while avoiding the expensive microscopes, spectrometers, and complex imaging platforms often required to read high-security PUFs. In principle, authentication could be performed with tools already found in everyday environments, although practical commercial systems would likely combine the light sources with a smartphone application or dedicated optical reader.
The team also demonstrated that the nanostructures could be transferred to several kinds of substrates, an important step toward real-world deployment. The structures were applied to flexible plastics, metals, transparent films, and hydrogels, which are soft, water-rich materials capable of holding substantial amounts of moisture. This range suggests that the method is not restricted to rigid laboratory samples. A flexible version could be integrated into packaging or attached to curved surfaces, while a transparent film could function as a security sticker without hiding a product’s design. On electronics, the same technology could provide a hardware identity linked to an individual device or Internet of Things component, helping manufacturers verify products throughout distribution and service.
The researchers envision applications extending from anti-counterfeiting labels to device-level security. A manufacturer could register the flashlight and laser responses of each nanostructure during production, creating a reference record associated with a specific product. Later, an inspector, retailer, customs officer, or consumer could illuminate the label and compare the observed signals with that record. Luxury handbags, pharmaceuticals, collectibles, artworks, identification documents, and high-value industrial components are all potential targets. For connected devices, a physical identifier could complement software authentication and help establish whether hardware has been replaced, cloned, or tampered with. The approach may also be useful where transparency, flexibility, or low-cost inspection is more important than maximum data capacity.
The work was led by Professor Sang Ouk Kim of KAIST’s Department of Materials Science and Engineering in collaboration with Professor Seok Joon Kwon’s team at Sungkyunkwan University. Dr. Geon Gug Yang of KAIST and Seong-Gyun Im of Sungkyunkwan University contributed equally as co-first authors, while Kim and Kwon served as co-corresponding authors. Their study, titled “Dual-space visible light authentication toward high security physical unclonable function,” was published online in Nature Communications on July 23, 2026. The researchers say the key advance is the combination of a randomly generated structure that is extremely difficult to clone with an authentication method based on familiar light sources. Supported by Korea’s Ministry of Science and ICT and the Samsung Research Funding & Incubation Center for Future Technology, the work points toward security labels that are microscopic in scale but simple enough to verify in everyday life.
Subject of Research: Nanoparticle-based physical unclonable functions for anti-counterfeiting and device authentication
Article Title: Dual-space visible light authentication toward high security physical unclonable function
News Publication Date: August 26
Web References: https://doi.org/10.1038/s41467-026-75781-4
References: Nature Communications, article published online July 23, 2026; DOI: 10.1038/s41467-026-75781-4
Image Credits: KAIST
Keywords
Physical unclonable function, PUF, nanoparticle self-assembly, nanofingerprint, anti-counterfeiting, optical authentication, laser scattering, smartphone flashlight, cybersecurity, KAIST, Nature Communications
