“…To achieve sensing of different redox states of iron, various methods have been explored but with limited success either in living cells or in vivo. For example, laboratory techniques, such as inductively coupled plasma mass spectrometry (12,13), electron paramagnetic resonance (14), x-ray fluorescence (15), and magnetic resonance imaging (MRI) (16)(17)(18) have been developed but cannot readily provide spatial or temporal information in vivo because of their restrictive requirements for sample pretreatment or excessive time needed for data collection. It has been shown that "labile" iron pools, which comprise only a small portion of total iron, play critical roles in many cellular processes, including lipid oxidation during ferroptosis and generating free radicals in AD (19)(20)(21), and all of the above methods can measure only the total iron without differentiating labile iron pools.…”