A new long-wavelength fluorigenic substrate for alkaline phosphatase: synthesis and characterisation

Naphthofluorescein diphosphate has been synthesised from the parent dye, an d shown to be an attractive long-wavelength alternative to other fluorigeni c substrates for the determination of alkaline phosphatase, Its application to the determination of theophylline, an inhibitor of this enzyme, has bee n demonstrated. The optimum excitation wavelength of the hydrolysis product naphthofluorescein has been found to depend on the presence of additives s uch as cyclodextrins and (3-[3-cholamidopropyl]-dimethylamino)-1-propane su lfonate (CHAPS): such effects can be used to raise the excitation wavelengt h to match the output of a 635 nm diode laser in a simple and sensitive flu orescence detector.