Making invisible inks more invisible

Invisible inks based on “smart” fluorescent materials have been shining brightly (if only you could see them) in the data-encryption/decryption arena lately. Researchers have debuted various organic dyes, nanocrystals, and other materials to help keep confidential information secure and to develop anticounterfeiting strategies. But some of the materials are costly or difficult to prepare, and many of these inks remain somewhat visible when...