A cipher key was written in the form of a defined monomer sequence, dissolved in isopropanol and mixed with glycerol and soot. This created an ink that was used to write a letter. The 256-bit cipher key was successfully recovered by the recipient of the letter by extracting with dichloromethane and following instructions for sequencing.
https://pubs.acs.org/doi/pdf/10.1021/acscentsci.2c00460