Counterfeit seeds can cost farmers more than two-thirds of expected crop yields. Now an MIT team may have found a way to outwit fakers: tiny tags of biodegradable silk-based material, each containing a unique combination of chemical signatures.

The technology is based on what are known as physically unclonable functions, or PUFs, a concept used to protect the authenticity of computer chips.

Using drop casting, in which a drop of liquid containing a suspension of the desired materials is deposited on a surface, dean of engineering Anantha Chandrakasan and his colleagues produced tags less than a tenth of an inch in diameter. Then they found a way to add color to silk microparticles and mix four basic types to create random patterns. 

“With a minimal amount of silk, we were able to generate 128 random bits of security,” says Benedetto Marelli, a professor of civil and environmental engineering and a coauthor of the paper. The patterns can be read out by a cell-phone camera with a macro lens, processed locally to generate the PUF code, and sent to the cloud and compared against a secure database.

As Marelli says, it’s democratic—“something that you can literally read with your phone, and you can fabricate by simply drop-casting a solution, without using any advanced manufacturing technique.”