Nano-inks, which are usually formed by dispersing a nanostructured material in some solvent, have shown great promise as security inks that can be used to develop anticounterfeiting technologies. A variety of nanomaterials such as carbon-based zero-dimensional materials (carbon dots and graphene quantum dots), semiconductor quantum dots, lanthanide nanocrystals, nano-polymers, nanostructured perovskites, metal organic frameworks have been investigated for potential applications as security inks. Nanostructured material-based inks are preferred as security inks owing to their unique and robust photophysical properties, ease of functionalization, fast stimulus-responsive system, and cost-effectiveness. Different types of luminescence observed in a wide variety of nanoscale materials are usually employed to make security marks that are invisible under visible light but become distinct under some external stimuli. Based on this simple principle, high-security data encryption and decryption with nano-inks have been demonstrated. In this chapter, we discuss the various types of nanostructure-based security-inks developed, their strengths and limitations, projected applications, and the governing mechanisms of each application.
