A biosensor that can detect the minute quantities of zinc in our bodies could settle the debate once and for all as to whether zinc dietary supplements are good or bad. Millions of people take zinc supplements in the belief that they may have a deficiency of this essential trace element, especially when they are suffering from the common cold. However, there is scant evidence of what zinc levels in our bodies should be. Now, Rebecca of the University of Maryland and colleagues there and at the University of Michigan have developed an engineered fluorescent protein whose glow in the presence of zinc can be seen under the microscope. The team suggests that the new technique will help improve our understanding of the biological role of zinc as well as expose details of its involvement in plaque formation in Alzheimer's disease, how prolonged seizures or stroke kill brain cells, and how the cell normally allocates zinc to different proteins.