Hard X-ray excited optical luminescence from protein-directed Au∼20 clusters

Hard X-ray excited optical luminescence is a unique property of materials, which makes them promising for biological imaging applications. However, the preparation of biocompatible contrast agents for hard X-ray excited optical luminescence remains a considerable challenge that has, to date, not been overcome. In this study, we investigated the luminescence properties of protein-directed Au∼20 clusters upon hard X-ray irradiation, both in solution and when embedded in films.