A one-step potentiometric immunoassay for plasma cardiac troponin I using an antibody-functionalized bis-MPA–COOH dendrimer as a competitor with improved sensitivity
Herein, we have reported a new one-step potentiometric immunoassay for the sensitive and specific detection of human plasma cardiac troponin I (cTnI), a biomarker of cardio-cerebrovascular diseases. Initially, the cTnI biomolecules were immobilized on the surface of a gold nanoparticle-functionalized screen-printed graphite electrode (SPGE). Thereafter, rabbit polyclonal antibodies to cTnI were covalently conjugated to the bis-MPA–COOH dendrimers through typical carbodiimide coupling. The introduction of the target analyte caused a competitive immunoreaction between the immobilized cTnI on the electrode and the conjugated antibody on the dendrimers. The potentiometric measurement was mainly derived from the change in the surface charge on the surface of the modified electrode due to the negatively charged bis-MPA–COOH dendrimers after the immunoreaction. On increasing target cTcI, the number of charged dendrimers on the immunosensor decreased, resulting in a change in the electric potential. Under optimum conditions, the potentiometric immunosensor exhibited good potentiometric responses for the detection of cTcI and allowed the determination of the target analyte at a concentration as low as 7.3 pg mL−1. An intermediate precision of ≤8.7% was accomplished with batch-to-batch identification. Meanwhile, the potentiometric immunosensor showed good anti-interfering capacity and selectivity against other proteins and biomarkers. Importantly, our system displayed high accuracy for the analysis of human plasma serum samples containing target cTcI relative to commercial human cTcI enzyme-linked immunosorbent assay (ELISA) kits.