Indicator displacement assays that detect bilayer membranes enriched in phosphatidylserine

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Abstract
Three indicator displacement assays are described for the detection of phosphatidylserine in a bilayer membrane. A series of Zn2+-dipicolylamine coordination compounds are used to bind selectively to the phosphatidylserine and act as a colorimetric chemosensing ensemble when combined with the UV-Vis indictor pyrocatechol violet. A similar displacement assay uses a coumarin methylsulfonate derivative as a fluorescent indicator, and a third assay involves quenching of calcein fluorescence by Cu2+ and subsequent fluorescence restoration upon addition of phosphatidylserine. In the best case, vesicle membranes containing as little as 5% phosphatidylserine could be detected under physiologically relevant conditions using as little as 10 µM sensing ensemble, and two of the three systems allow vesicles containing 50% phosphatidylserine to be detected by the naked eye.