To assess the activity of anionophores, several types of assays were developed, involving different methods to monitor ion concentrations, such as the use of ion selective electrodes or fluorescence spectroscopy. For the latter, emissive probes are encapsulated inside liposomes and give a response upon transmembrane transport. The change of interior anion concentration during the transport process can be monitored by probes responding to the anion of interest. To directly monitor chloride concentrations, the probes SPQ (6-methoxy-N-(3-sulfopropyl)quinolinium) and lucigenin (N,Nʹdimethyl-9,9ʹ-biacridinium dinitrate) are used. The first use of lucigenin to measure chloride transport in artificial vesicles was by the Verkman laboratory and the method was further adapted by McNally et al. to the current form of the lucigenin assay. Since then, the lucigenin assay became an attractive way to directly monitor transport of chloride (and other anions ) through lipid bilayers, which enables the study of anionophore activity.