A new electrochemiluminescence immunosensor based on Ru(bpy)32+-doped TiO2 nanoparticles labeling for ultrasensitive detection of human chorionic gonadotrophin

A sensitive electrochemiluminescence (ECL) immunosensor was constructed on the basis of sandwich-type immunoreaction with Nafion functionalized TiO2 composite nanoparticles as label. The composite nanoparticles labeled antibody were synthesized by successively loading the antibody and large amounts of Ru(bpy)32+ molecules onto the Nafion coated TiO2 nanoparticles, which is named as Ru–Nafion@TiO2 labeled secondary antibody. They together with the electrodeposited gold nanoparticles (DpAu) were employed to assemble the ECL immunosensor as following procedure. Firstly, The DpAu was modified on gold electrode to adsorb primary antibody. Then the detected antigen and Ru–Nafion@TiO2 labeled secondary antibody was conjugated one after another to form a sandwich-type immunocomplex and generate an ECL signal related to the content of analytes. DpAu nanoparticles and composite TiO2 nanoparticles amplified the ECL response signal via increasing the carrier content of primary antibody and ECL signal labels. The capability of the immunosensor was evaluated by detecting the ECL responses of immunosensor on different concentrations of human chorionic gonadotrophin (HCG). Comparing with other immunoassay, the sandwich-type ECL immunosensor assembled with DpAu and Ru–Nafion@TiO2 nanoparticles can perform the ultrasensitive detection to HCG with a low detection limit of 0.007 mIU/mL.