Novel colorimetric immunoassay for ultrasensitive monitoring of brevetoxin B based on enzyme-controlled chemical conversion of sulfite to sulfate.

A simple colorimetric immunoassay for quantitative monitoring of brevetoxin B on a functionalized magnetic bead by using glucose oxidase (GOx)/antibrevetoxin antibody-labeled gold nanoparticle as the signal transduction tag was developed. The assay was carried out on the basis of GOx-controlled sulfite-to-sulfate chemical conversion with a silver(I)-3,3',5,5'-tetramethylbenzidine [Ag(I)-TMB] system. Initially, the sulfite was used as an inhibitor of Ag(I) to hinder the color development of TMB due to the formation of insoluble silver sulfite. Accompanying H2O2 generation with GOx-catalyzed glucose, the sulfite was converted into the sulfate, thus resulting in the colorless-to-blue change. Under the optimal conditions, the absorbance decreased with increasing brevetoxin B from 0.5 to 200 ng/kg with a detection limit of 0.1 ng/kg (ppt). The precision and specificity were acceptable. Furthermore, the methodology gave results matching well with the referenced brevetoxin ELISA kit for monitoring of spiked Musculista senhousia samples.