Copper-doped NH2-metal–organic frameworks as co-reactant modulating units for a sensitive electrochemiluminescence immunoassay†

A facile electrochemiluminescence (ECL) immunosensor for the sensitive detection of the prostate-specific antigen (PSA) was constructed based on a co-reactant modulating strategy using a Cu²⁺-modified NH₂-metal–organic framework (NMOF@Cu²⁺) nanoprobe as a modulating unit. The biconical NMOF@Cu²⁺ nanoprobe possessed a large number of carboxyl groups, which could be labeled by the target PSA to form a PSA–NMOF@Cu²⁺ conjugate. Moreover, the nanoprobe could consume K₃[Fe(CN)₆], resulting in a lower signal of the luminol–K₃[Fe(CN)₆] ECL system. The bioassay was executed in a split-type mode. First, the competitive immunological recognition reaction with the PSA–NMOF@Cu²⁺ conjugate as the signal probe was performed in an antibody labeled 96-well plate. In the presence of the target PSA, the PSA competes with the PSA–NMOF@Cu²⁺ conjugate for immobilization, which determines the amount of PSA–NMOF@Cu²⁺ conjugates immobilized in the plate and results in different amounts of prefilled K₃[Fe(CN)₆] being consumed. Subsequently, the above solution was transferred to the detection cell for ECL testing, whereby the ECL signal from the luminol–K₃[Fe(CN)₆] system reflected the content of the PSA. The developed ECL immunosensor showed high sensitivity for the PSA with a linear response range of 1.0 pg mL⁻¹–10 ng mL⁻¹ and a detection limit of 0.5 pg mL⁻¹. Moreover, the applicability of the present method was demonstrated by the determination of the PSA in human serum.