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 to form an ABEI-PEI-Au@AgNCs-PAA/Co complex, which could introduce Co as a catalyst to promote HO decomposition and thus oxidize ABEI to produce an enhanced ECL signal. Here, the obtained self-enhanced ABEI-PEI-Au@AgNCs-PAA/Co complex is utilized to capture the detection antibody (Ab). 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 to 200 ng mL and a detection limit of 3.3 fg mL.