Popeye, the comic book hero, swears by it as do generations of parents who delight their children with spinach. Of course, today it is known that the vegetable is not quite as rich in iron as originally thought, but that iron is nevertheless essential for our physical well-being is undisputed. Lack of iron — caused by malnutrition — can lead to anemia while an increased level of iron may signal the presence of an acute inflammatory response. Therefore, the blood iron level is an important medical diagnostic agent. Researchers have now developed a novel biosensor for determination of iron content that is based on nanodiamonds.