Near-Infrared Turn-On Fluorogenic Probe for Versatile Detection of Inorganic Polyphosphates

Inorganic polyphosphate (polyP) is a ubiquitous phosphate biopolymer involved in diverse cellular processes. Despite its significance, selective detection of polyP remains challenging because of its simple and highly charged structure. Here, we report a near-infrared (NIR) fluorogenic turn-on chemosensor for selective polyP detection and imaging, SiX-DPA-Zn. The probe combines a silicon-xanthene (SiX) fluorophore with a zinc(II)-coordinated 2,2'-dipicolylamine (DPA-Zn2+) recognition unit and shows more than 100-fold selectivity for inorganic polyP over ADP and ATP. SiX-DPA-Zn enables quantitative detection of polyP at micromolar concentrations in microplate assays and stains a broad range of polyP species, starting from tripolyphosphate, in polyacrylamide gels. In HEK293 cells expressing Escherichia coli polyphosphate kinase 1, the probe visualizes intracellular polyP and enables quantitative analysis of polyP levels in relation to nuclear proteins for example fibrillarin and nucleolin. Stimulated emission depletion (STED) microscopy further revealed subdiffraction-sized polyP granules within polyP aggregates. SiX-DPA-Zn is the first near-infrared (NIR) fluorogenic chemosensor for polyP that is compatible with multiple detection platforms, including microplate assays, polyacrylamide gel staining, confocal and super-resolution STED microscopy.