Open day activities rarely give applicants a real sense of the practical and intellectual work that goes on in university chemistry departments. We devised an experiment for year 13 (age 17-18) students based on the size-dependent colours of gold nanoparticles and linked this to current research in diagnostic medicine. The experience was designed to demonstrate the benefits of nanotechnology but it did so through the allure of gold. (Contains 5 figures and 1 table.)