Current Techniques for Inorganic Polyphosphate Detection and Characterisation.

Polyphosphate (polyP) is an evolutionarily conserved linear polymer of orthophosphate residues with diverse functions across organisms from bacteria to mammals. In addition to its roles in phosphate and energy storage, polyP has been implicated in thrombosis, inflammation, cancer, metabolism, cytoskeletal regulation, and neurodegenerative diseases. PolyP also acts as a molecular scaffold interacting with lysine-rich proteins and may contribute to protein folding and amyloid formation. However, biochemical heterogeneity, including variation in chain-length, subcellular localisation, and supramolecular organisation together with the absence of clearly defined mammalian biosynthetic pathways, has limited mechanistic understanding of polyP biology. Reliable detection and quantification remain challenging because current methods often suffer from limited specificity, chain length bias, insufficient quantitative robustness, and interference from other highly anionic biomolecules such as DNA or RNA. This review summarises current methodologies for polyP detection and characterisation. Emerging polyP-specific probes, including recombinant polyP-binding domains derived from polyphosphatases and conserved histidine α-helical domains may improve qualitative and quantitative analysis of polyP in complex biological systems. Improved analytical strategies will be essential to define the physiological roles of polyP and evaluate its potential as a biomarker and therapeutic target.