Storing medical information under the skin’s surface, Every year, a lack of vaccination leads to about 1.5 million preventable deaths, primarily in developing nations.

One factor that makes vaccination campaigns in those nations more difficult is that there is little infrastructure for storing medical records, so there’s often no easy way to determine who needs a particular vaccine.

MIT researchers have now developed a novel way to record a patient’s vaccination history storing the data in a pattern of dye, invisible to the naked eye, that delivered under the skin at the same time as the vaccine.

The researchers showed that their new dye, which consists of nanocrystals called quantum dots, can remain for at least five years under the skin, where it emits near-infrared light that can detected by a specially equipped smartphone.

To create an “on-patient,” decentralized medical record, the researchers developed a new type of copper-based quantum dots, which emit light in the near-infrared spectrum. The dots are only about 4 nanometers in diameter, but they are encapsulated in biocompatible microparticles that form spheres about 20 microns in diameter. This encapsulation allows the dye to remain in place, under the skin, after injected.

The researchers designed their dye to delivered by a microneedle patch rather than a traditional syringe and needle. Such patches are now developed to deliver vaccines for measles, rubella, and other diseases, and the researchers showed that their dye could be easily incorporated into these patches.

The microneedles used in this study 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 applied to the skin, the microneedles, which are 1.5 millimeters long, partially dissolve, releasing their payload within about two minutes.

By selectively loading microparticles into microneedles, the patches deliver a pattern in the skin that is invisible to the naked eye but can scanned with a smartphone that has the infrared filter removed. The patch can customized to imprint different patterns that correspond to the type of vaccine delivered.

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

The researchers also tested this vaccination strategy in rats, using microneedle patches that delivered the quantum dots along with a polio vaccine. They found that those rats generated an immune response like the response of rats that received a traditional injected polio vaccine.

The researchers now plan to survey health care workers in developing nations in Africa to get input on the best way to install this type of vaccination record keeping.

The researchers believe the quantum dots are safe to use in this way because they encapsulated in a biocompatible polymer, but they plan to do further safety studies before testing them in patients.

This study presents a novel approach where the medical record stored and controlled by the patient within the patient’s skin in a minimally invasive and elegant way.