Immune monitoring in vaccination, infection, cancer and autoimmunity requires detection of certain antigen-specific immune cells, yet their low frequency and dispersed distribution makes finding them a challenge. A platform from the Hammond and Irvine labs cleverly exploits memory T cell functioning to concentrate target circulating immune cells in the skin for non-invasive sampling by a microneedle patch; recently published in Nature Biomedical Engineering, earlier work on this approach was supported by the Bridge Project and appears in the KI Image Awards Archive.