Intramolecular Self-Enhanced Nanochains Functionalized by an Electrochemiluminescence Reagent and Its Immunosensing Application for the Detection of Urinary β2-Microglobulin

In this study, polyethylenimine (PEI) is discovered to possess a noticeable amplification effect for the electrochemiluminescence (ECL) of N -(aminobutyl)- N -(ethylisoluminol) (ABEI); thus, a novel self-enhanced ECL reagent (ABEI–PEI) is prepared by covalent cross-linking. Because of the shortened electron-transfer path and reduced energy loss, the intramolecular ECL reaction between ABEI and PEI exhibited enhanced luminous efficiency compared with the traditional intermolecular ECL reaction. Owing to the amine-rich property of PEI, abundant ABEI could be immobilized on the molecular chains of PEI to strengthen the luminous intensity of ABEI–PEI. On account of the reducibility of remaining amino groups, ABEI–PEI, as the self-enhanced ECL reagent, has also been chosen as a reductant and stabilizer for in situ preparation of Au@Ag nanochains (Au@AgNCs) which has the catalytic activity for the ECL reaction. Moreover, using ABEI–PEI as a template to directly prepare Au@AgNCs realizes the immobilization of the ECL reagent with large amounts. Meanwhile, in virtue of the electropositivity of ABEI–PEI-capped Au@AgNCs (ABEI–PEI–Au@AgNCs), polyacrylic acid (PAA) with electronegativity is pervaded on the surface of nanochains and further chelates with Co 2+ to form an ABEI–PEI–Au@AgNCs–PAA/Co 2+ complex, which could introduce Co 2+ as a catalyst to promote H 2 O 2 decomposition and thus oxidize ABEI to produce an enhanced ECL signal. Here, the obtained self-enhanced ABEI–PEI–Au@AgNCs–PAA/Co 2+ complex is utilized to capture the detection antibody (Ab 2 ). According to sandwiched immunoreactions, a sensitive ECL immunosensor is constructed for the detection of β2-microglobulin with a wide linearity from 0.01 pg mL –1 to 200 ng mL –1 and a detection limit of 3.3 fg mL –1 .