ION Potassium Green - 4, potassium indicator, membrane impermeable. Formerly known as Asante Potassium Green - 4 (APG-4). Compatible with a wide variety of detectors including fluorescent microscopes, plate readers, flow cytometers, and fluorescent indicator-doped solid-state sensors. Excitation: 525 nm | Emission: 545 nm | Kd: 7 mM The IPG family of indicators are the best-in-class replacements for the legacy K⁺ indicator, PBFI. Unlike PBFI, the spectral properties of the IPG family of K⁺ indicators make them convenient to use with common filter sets (e.g. YFP and FITC) as well as multiphoton approaches, and the range of K⁺ affinities make them useful for applications as diverse as extracellular K⁺ sensing to monitoring intracellular K⁺ dynamics. These molecules are small, synthetic fluorochromes which incorporate a K⁺-binding moiety. Under conditions where K⁺ is not bound, the fluorescence of the sensor is significantly quenched. When K⁺ is bound, the quenching is relieved, and the fluorescence of the sensor dramatically increases. IPG-4 TMA⁺ salt is a membrane impermeable form of IPG-4 that can be used in lipid membrane-free systems, in liposomes, or can be introduced into cells by electroporation, microinjection or other methods.