3-(10′-Phenothiazinyl)propane-1-sulfonate is a potent enhancer of soybean peroxidase-induced chemiluminescence

3-(10′-Phenothiazinyl)propane-1-sulfonate (SPTZ) was shown to be a potent enhancer of soybean peroxidase (SbP)-induced chemiluminescence. To the best of our knowledge, SPTZ is the first enhancer of SbP to be discovered. Optimal conditions for SbP-catalyzed oxidation of luminol in the presence of SPTZ were determined. The SbP–SPTZ system showed better sensitivity and a lower detection limit (LDL) with respect to the horseradish peroxidase–4-iodophenol system traditionally used in chemiluminescent enzyme-linked immunosorbent assay (ELISA). The addition of 4-morpholinopyridine (MORP) to the SbP–SPTZ system improved its analytical parameters by decreasing the LDL of SbP to 0.03 pM. These results open up very promising perspectives for using the SbP–SPTZ–MORP system in ultrasensitive immunoassay.