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A custom ink stores data in stable polymers

New mass spectrometry method decodes the data by reading the polyurethane strands and placing the monomers in the correct order

by Craig Bettenhausen
August 9, 2022


A gloved hand holds the cartridge for a gel-ink pen.
Credit: ACS Cent. Sci.
Eric V. Anslyn’s team loaded a polymer ink that can encode data into this commercial gel pen.

It’s hard to beat the personal touch of a handwritten note. But a playful letter that chemist Eric V. Anslyn of the University of Texas at Austin recently sent to his collaborators carried something even more unique: the ink was loaded with polymer strands encoding digital data (ACS Cent. Sci. 2022, DOI: 10.1021/acscentsci.2c00460).

Chemists and computer scientists have been exploring ways to store data into polymer strands, inspired by DNA’s ability to store and transmit enough information to build complex organisms with mere picograms of material. Although DNA is relatively robust and data-dense and has a well-developed array of sequencing and synthesis technologies, other types of polymers could be more stable and could more easily go beyond the four-letter codes DNA allows. But data storage using inert polymers has been limited so far by the difficulty of preparing and reading long strands.

In one such approach, Anslyn and James F. Reuther of the University of Massachusetts Lowell have been developing a system to encode data using polyurethane oligomers, strings of different monomers connected with urethane linkages. They had previously made a series of 16 urethane monomers, with side chains similar to amino acids, that could be precisely assembled into programmed, 10-unit sequences, each of which can encode 32 bits. In the current study, they developed a mass spectrometry method to read out the sequences in a mixture of these strands, which can be designed to encode any kind of data.

To test the system, Anslyn and his group coded a 256-bit encryption key into eight oligomers and formulated the mixture into ink for a ball-point pen. Using that ink, the researchers wrote a short note with a drawing (shown) and mailed it to Reuther to decode using the new method.

A note handwritten in yellowish ink that reads: Dear Professor Reuther, I hope this letter finds you well in Lowell! The molecular encoding project is moving along nicely. I look forward to chatting soon! Best regards, Anslyn Lab
Credit: ACS Cent. Sci.
This note that Eric V. Anslyn sent to James F. Reuther hides data: a 256-bit encryption key is encoded into an oligomer in the ink.

When the letter arrived in Massachusetts, Reuther and his group extracted the ink from the paper and used a mass spectrometry and depolymerization protocol the collaborators designed to sequence the strands and place the monomers in the correct order. With a reassembled key in hand, the team used it to unlock an encrypted file Anslyn had sent separately.

What they found was a complete digital copy of L. Frank Baum’s 1900 novel, The Wonderful Wizard of Oz. “It’s one of my favorite childhood books,” Anslyn says. “The goal was to show that we could sequence several oligomers simultaneously in one run.”

Anslyn says that DNA data storage has a head start over abiotic polymers such as polyurethane in that the technology used to read DNA is much more mature. “But DNA uses only four symbols, A, T, C, and G,” he says. “In this particular paper, we’re using 16 symbols. And hence, the information density starts to go up.”

The work demonstrates the largest amount of information successfully encoded and decoded in a single sample of such oligomers, says materials scientist Charles M. Schroeder of the University of Illinois at Urbana-Champaign, in an email.

Rigoberto (Gobet) Advincula, a polymer and materials scientist at the University of Tennessee, Knoxville, says that any urethane monomer that could polymerize with the others could be added into the system to allow even greater data density. Advincula also notes that polyurethane chemistry is well developed and mass spectrometry instrumentation is readily available, so this approach could be replicated in existing labs.


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