Fe3O4@PDA immune probe-based signal amplification in surface plasmon resonance (SPR) biosensing of human cardiac troponin I

This work reports immunomagnetic separation technology-assisted surface plasmon resonance (SPR) biosensing for human cardiac troponin-I (cTnI), a well-known diagnostic marker for myocardial damage. Au film modified by Au nanoparticles (AuNPs) and polydopamine (PDA) was employed as the platforms for immobilizing capture antibody (cAb) and SPR sensing. Magnetic immune probe was prepared by attaching detection antibody (dAb) on the surface of Fe3O4 nanoparticles (Fe3O4 NPs) coated by PDA for precise capture, magnetic separation and enrichment of target analyte (cTnI) from samples. This extraction process greatly improves the sensitivity and effectively reduces the nonspecific interference from complex matrixes. The analyte cTnI collected via Fe3O4@PDA-dAb immune probe can be specially recognized by cAb immobilized on the sensing platform. By introducing secondary antibody (Ab(2)) conjugated with multi-walled carbon nanotube-PDA-AgNPs (MWCNTs-PDA-AgNPs/Ab(2)) to the sensing system, the residual binding sites of cTnI were occupied, and the SPR response signals were further amplified. The obtained detection limit for cTnI is 3.75 ng mL(-1), which is 320-folds lower than that achieved by PDA-based sensing strategy. The present method was applied to the examination of serum samples spiked with cTnI, and the good recoveries demonstrate its future applicability in clinical diagnosis.