Security inks with silanized zinc oxide quantum dots and cellulose ethers for the safeguarding of cultural heritage objects

As crimes involving cultural heritage objects continue to escalate globally, there is a growing demand for new technology-aided interventions. Tagging the objects with security inks can be crucial in crime deterrence and evidence-based validation. In this work, security inks were specifically formulated with zinc oxide (ZnO) quantum dots as the fluorescent agent and nonionic cellulose ethers as the binder for application on artwork surfaces. Comparing naked and silanized nanoparticles, those modified with (3-aminopropyl)triethoxysilane (APTES) exhibited complete dispersibility in water, better fluorescence stability in water against UV light exposure and temperature variation, and tuneable emission properties –allowing the generation of robust, high-level security tags. Meanwhile, the inclusion of nonionic cellulose ethers significantly improved the readability of the ink under 365-nm UV light while retaining invisibility under D65 standard light. The promising formulation containing 3.0 wt. % of ZnO@APTES and 0.5 wt. % methyl 2-hydroxyethyl cellulose in water demonstrated compatibility across several substrates (papers, stone, and ceramic), workability with various application techniques (pen-writing, brushing, stamping), and strong resistance to degradation over three cycles of weathering tests.