Metabolic changes in cells can occur at the earliest stages of disease. In most cases, knowledge of those signals is limited, since we usually detect disease only after it has done significant damage. Now, a team led by engineers at Tufts University School of Engineering has opened a window into the cell by developing an optical tool that can read metabolism at subcellular resolution, without having to perturb cells with contrast agents, or destroy them to conduct assays. As reported today in Science Advances, the researchers were able to use the method to identify specific metabolic signatures that could arise in diabetes, cancer, cardiovascular and neurodegenerative diseases.