ESIPT fluorescence turn-on sensors for detection of short chain inorganic polyphosphate in water

We introduce two water-soluble excited state intramolecular proton transfer (ESIPT) based fluorescent turn-on probes responding to inorganic polyphosphates. These ESIPT probes enable specific detection of short-chain inorganic polyphosphates over a range of different condensed phosphates. The probes are weakly emissive in their off-state due to the blocking of ESIPT by Cu²⁺ coordination. Removal of the copper ion through decomplexation by the analyte accesses the on-state. The probes detect polyphosphates over other biologically occurring phosphates, pyrophosphate, and nucleotides such as ATP, ADP, GTP. An optimal fluorescence response is observed with the short-chain polyphosphate polyP₈. Furthermore, the probe shows selectivity towards linear polyphosphates over cyclic metaphosphates. The rapid 'turn-off-turn-on' fluorescence responses upon consecutive addition of Cu²⁺ and polyP₈ are reversible, further highlighting sensor performance in an aqueous environment. One of the sensors is then used to monitor polyP digestion by an exopolyphosphatase (PPX).