Medical history that’s skin deep

US researchers are developing a specialised dye that could allow a person’s vaccination record to be injected into their body at the same time as a vaccine.

It would then be stored beneath the skin, avoiding the all-too-common problem of vaccination details being lost, and follow-up vaccinations missed.

It’s early days, but work to date with rats and human cadaver skin has been promising.

Writing in the journal Science Translational Medicine, a team from the Massachusetts Institute of Technology reports that their new dye, made from nanocrystals called quantum dots, can remain for at least five years under the skin, where it emits near-infrared light that can be detected by a specially equipped smartphone.

The copper-based dots are only about four nanometres in diameter but are encased in biocompatible microparticles that form spheres about 20 microns in diameter. This allows the dye to remain in place under the skin after being injected, the researchers say.

They designed their dye to be delivered by a microneedle patch rather than a traditional syringe and needle. Such patches are now being developed to deliver vaccines for measles, rubella, and other diseases.

The microneedles used in the study are made from a mixture of dissolvable sugar and a polymer called PVA, as well as the quantum-dot dye and the vaccine.

When the patch is applied to the skin, the microneedles, which are 1.5 millimetres long, partially dissolve, releasing their contents in about two minutes.

By selectively loading microparticles into microneedles, the researchers say, the patches deliver a pattern in the skin that is invisible to the naked eye but can be scanned with a smartphone that has the infrared filter removed.

The patch can be customised to imprint different patterns that correspond to the type of vaccine delivered.

“It’s possible someday that this invisible approach could create new possibilities for data storage, biosensing and vaccine applications that could improve how medical care is provided, particularly in the developing world,” says Robert Langer, one of the paper’s senior authors.

Tests using human cadaver skin showed that the quantum-dot patterns could be detected by smartphone cameras after up to five years of simulated sun exposure.

Tests in rats showed that the quantum dots did not affect the efficacy of the polio vaccine they were injected.

The researchers are working on expanding the amount of data that can be encoded in a single pattern, allowing them to include information such as the date of vaccine administration and the lot number of the vaccine batch.

Further safety studies will be undertaken before testing on human patients.