Using fluorescent quantum dots, an MIT research team has created a way to administer vaccinations and record a patient’s vaccination history in the skin. The researchers developed a microneedle platform that can selectively deliver microparticles into the skin in various patterns, which remain invisible to the naked eye but can be detected in the infrared (IR) using a smartphone that has the IR filter removed. The microparticles contain quantum dots, which store the person’s vaccination history in a pattern of dye that is delivered under the skin at the same time as the vaccine. The copper-based quantum dots emit light in the near-infrared (NIR) spectrum and are about 4 nm in diameter. They are encapsulated in the biocompatible microparticles, which are about 20 μm in diameter. Encapsulation allows the dye to remain in place, under the skin, after being injected. The researchers encapsulated quantum dots in microspheres made of PMMA, a material that improves biocompatibility. Courtesy of K.J. McHugh et al., Science Translational Medicine (2019). The microneedles used in the study were made from a mixture of dissolvable sugar and a synthetic, water-soluble polymer, as well as the dye and the vaccine. When the patch is applied to the skin, the microneedles, which are 1.5 mm long, partially dissolve, releasing their contents within about 2 min. The patch can be customized to imprint different patterns that correspond to the type of vaccine being delivered. Tests using human cadaver skin showed that the quantum-dot patterns could be detected by modified smartphone cameras after up to five years of simulated sun exposure. A close-up microscope image of the microneedle array, which could be used to deliver quantum dots into skin. Courtesy of K.J. McHugh et al., Science Translational Medicine (2019). The researchers also tested their vaccination strategy in rats, using microneedle patches that delivered the quantum dots along with a polio vaccine. They found that the rats generated an immune response similar to the response of rats that had received a traditionally injected polio vaccine. Patterns were detected nine months after the intradermal delivery of microparticles in the rats. “This study confirmed that incorporating the vaccine with the dye in the microneedle patches did not affect the efficacy of the vaccine or our ability to detect the dye,” researcher Ana Jaklenec said. The quantum dots after being administered to the skin of rodents. Courtesy of K.J. McHugh et al., Science Translational Medicine (2019). Medical record-keeping is essential for proper vaccination coverage. However, maintaining or accessing records can be difficult, particularly in low-resource settings that lack centralized databases. The MIT researchers now plan to survey health care workers in developing nations to get input on the best way to implement this approach to vaccination record-keeping. They are also working on expanding the amount of data that can be encoded in a single pattern, to allow information such as the date of vaccine administration and the lot number of the vaccine batch to be included in the quantum-dot dye pattern. The researchers believe the quantum dots are safe to use in the skin because they are encapsulated in a biocompatible polymer, but they plan to do further safety studies before testing them in patients. The research was published in Science Translational Medicine (www.doi.org/10.1126/scitranslmed.aay7162).