Determination of trace human chorionic gonadotropin by using multiwall carbon nanotubes as phosphorescence labeling reagent

Taking advantage of the cutting effect of the strong oxidation of benzoyl peroxide [(C6H5CO)2O2] on the end of multiwall carbon nanotubes (MWNTs) to obtain water-soluble multiwall nanotubes (MWNTs') and the spiking effect of polyacrylamide (PA) on the room temperature phosphorescence (RTP) of MWNTs', a new phosphorescent labeling reagent, MWNTs'-PA, has been developed in this study. The product β-AbHCG-MWNTs'-PA obtained by MWNTs'-PA labeling human chorionic gonadotropin-β-subunit three-dimensional core monoclonal antibody (β-AbHCG) not only could maintain good RTP characteristics of MWNTs' but also could take specific immunoreaction with β-HCG to form β-HCG- β-AbHCG-MWNTs'-PA, resulting in the increase of MWNTs' RTP signal. Thus, a new solid substrate room temperature phosphorescence immunoassay (SSRTPIA) for the determination of β-HCG has been established. The limits of detection (LODs) of the new method were 0.021 pg spot−1 for the direct way at 447/615 nm (λexmax/λemmax) and 0.016 pg spot−1 for the sandwich way at 447/614 nm (λexmax/λemmax). This sensitive, accurate, and precise method was used to determine β-HCG and diagnose human diseases by the direct way or the sandwich way, with the results coinciding with those obtained by chemiluminescence immunoassay. Meanwhile, the mechanisms of MWNTs' labeling β-AbHCG and determining β-HCG are also discussed.