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 is 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 be detected by a specially equipped smartphone. The researchers 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. "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," [study co-author Robert] Langer says. 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. The research was funded by the Bill and Melinda Gates Foundation and the Koch Institute Support (core) Grant from the National Cancer Institute.