These are ID tags of a different flavor.
Scientists in the U.K. have manipulated molecules that are capable of basic logic operations and could become an alternative to RFID tags. Complex procedures have been put together to create a technique called molecular computational identification (MCID). Such molecules can be manipulated using a certain mix of chemicals and give of light as a result. Such light-based output makes the molecules the equivalent to RFID tags. The difference is that these tags are, of course, very small.
Such a small ID tag would be useful in medical research, first and foremost, such as in tracking the progression of diseases or identifying genetic markers that can signal a danger of cancer. But the molecular ID tags can also be part of a greater purpose, a tiny version of the now controversial RFID tags that are making headlines as part of all kinds of diverse items, such as clothing and ID passports.
Whether the molecular tags can be made to function in such diverse situations remains to be seen, as does the long-term availability and success of the MCID methods, which are still in the advanced testing states. The scientists are confident, however, that their process can eventually be automated, which could lead to uses in things like nanostructure-based computer chips.