Information encryption strategy for optical security authentication using phosphor-encapsulated poly(N-isopropylacrylamide) nanoparticles

Abstract

Ultraviolet-induced fluorescence has proven an intriguing encoding strategy to increase the effectiveness of anti-counterfeiting measures for commercial materials. Recently, fluorescent inks showed severe disadvantages such as high costs, poor durability, and low efficiency. In this context, we present the development of a security encoding ink based on poly(N-isopropylacrylamide) (PNIPAM) nanoparticles immobilized with lanthanide-activated aluminate (LAA) nanoparticles (NPs), which can be used for advanced anticounterfeiting applications. LAA-encapsulated PNIPAM nanoparticles were prepared. Authentication inks based on LAA@PNIPAM nanoparticles provide a unique combination of photostability and endurance. Therefore, the composite ink containing LAA@PNIPAM nanoparticles exhibited strong reversible and photostable UV-induced fluorescence. Different composite inks with distinct emission properties were prepared by varying the concentration of LAA@PNIPAM nanoparticles. Paper sheets printed with a homogenous layer of the composite inks displayed a transparent appearance under visible lighting but became green beneath ultraviolet illumination, as proven by photoluminescence and CIE Lab tests. Using transmission electron microscopic (TEM) analysis, the morphological study of LAA particles displayed diameters of 3–8 nm, whereas LAA@PNIPAM nanoparticles displayed diameters in the range of 80–175 nm. Multiple methods were utilized to examine both structure and elemental composition of the fluorescent prints. The ink rheology and mechanical properties of prints were tested. The emission and excitation wavelength were detected at 519 (green color) and 365 nm (colorless), respectively. The present smart ink can be reported as a highly efficient technology for the production of anticounterfeiting commercial products.