The present invention describes new compositions of matter in the form of labeled nucleoside polyphosphates with four or more phosphates. In addition compositions of nucleoside polyphosphates with four or more phosphates that are substrates for nucleic acid polymerases with enhanced substrate properties and methods of using these nucleoside polyphosphates for nucleic acid detection, characterization and quantification are described. The compositions provided by this invention include nucleoside polyphosphate, dideoxynucleoside polyphosphate, or deoxynucleoside polyphosphate analogues which have colorimetric, chemiluminescent, or fluorescent moieties, mass tags or an electrochemical tags attached to the terminal-phosphate. When a nucleic acid polymerase uses this analogue as a substrate, an enzyme-activatable label would be present on the inorganic polyphosphate by-product of phosphoryl transfer. Removal of the polyphosphate product of phosphoryl transfer via phosphate or polyphosphate transferring enzyme leads to a detectable change in the label attached thereon. When the polymerase assay is performed in the presence of a phosphatase, there is provided a convenient method for real-time monitoring of DNA or RNA synthesis and detection of a target nucleic acid.