Researchers at Northwestern University have been studying how to use nanometer sized disks of gold and nickel to encrypt information. These nanodisks can form a pattern much like a barcode, which means that each pattern would have a unique response to a stimulus, such as electromagnetic radiation or light, depending on what type of molecule (or molecules) are attached to the disks. Their small size would also allow them to be invisible to the naked eye, and easily hidden in different materials or objects.

Chad Mirkin and his research group have made nanodisk arrays as long as 12 micrometers, which can support as many as 10 disk pairs, which yields 287 physical nanodisk codes. The researchers have functionalized these disks with dye molecules called chromophores that emit a unique light spectrum when illuminated with a laser beam. These disks could be used as biological labels in applications such as DNA detection, or as tags for tracking goods and personal.

Source: Nanodisk Codes