Vaccines save 2-3 million lives around the world annually. However, 1.5 million deaths from vaccine-preventable diseases still occur each year. Although many factors may lead to undervaccination, one important factor is the inability to accurately determine whether an individual has previously received a given vaccine, especially in developing countries where many people may not have vaccination records. 

Several alternatives to the traditional paper records have been proposed, including smartphone-based databases, fingerprinting and communication chips. However, these expensive options have not yet become prevalent due to difficulty in implementation. 

In a recent study published in the journal Science Translational Medicine, a group of researchers, including scientists from MIT and the Chinese Academy of Sciences, has come up with a cheap and easy-to-implement solution. They have designed a system to administer and detect very small nanoscale particles called quantum dots. The quantum dots are administered along with the vaccine and remain in the skin, serving as a vaccination record. 

First, the researchers had to synthesize the quantum dots, which are very small crystals, in the range of 2-10 nanometers. These particles are widely used in biomedical imaging, photovoltaic cells, and some TV screen displays. Scientists selected one type of quantum dot (called S10C5H) for its structural and functional stability under simulated sunlight. The quantum dots were then encapsulated in micro-sized capsules made of a special polymer. These encapsulated particles wrapped in pigmented human skin showed stability upon exposure to simulated sunlight up to an equivalent time of 5 years. The encapsulated polymers were packed in microneedles that were designed to dissolve in the skin.

The researchers subsequently treated rats with these dissolvable microneedles containing the polio vaccine and quantum dots (as the record of vaccine administration). No significant unaccounted tissue damage or toxicity was observed in the rats. The quantum dots could be visualized only under special LED lights in the near-infrared region (like the waves emitted by remote control), so they are invisible to the naked eye. For imaging purposes, researchers designed special lenses and imaging software for a Google Nexus 5X smartphone. Scientists found that the record-keeping quantum dots remained visible under near-infrared light for at least nine months. Furthermore, the dots did not seem to negatively impact the effectiveness of the vaccine: animals had antibody levels that were considered high enough to protect them from the disease.

For effective usage in the real world, clinical studies assessing biocompatibility and potential toxicity of the encapsulated dots will have to be done on humans. Overall, this study opens new and exciting possibilities for medical data storage, which could prove very valuable in eliminating vaccine-preventable diseases.