Ferritin-Based Electrochemiluminescence Nanosurface Energy Transfer System for Procalcitonin Detection Using HWRGWVC Heptapeptide for Site-Oriented Antibody Immobilization

In this study, an ultrasensitive biosensor based on a novel electrochemiluminescence nanosurface energy transfer (ECL-NSET) system was developed for procalcitonin (PCT) detection. N-(Aminobutyl)- N-(ethylisoluminol) (ABEI) as ECL donor was externally cross-linked with ferritin (ABEI-Ft), whose ECL emission was boosted by a ferritin nanocore in the presence of hydrogen peroxide. Then single gold nanoparticles (Au NPs) as ECL acceptor were in situ reduced on the ABEI-Ft surface to fabricate a donor-acceptor nanostructure (ABEI-Ft@Au). ECL quenching that occurred in ABEI-Ft@Au correlates well with the NSET theory rather than Förster resonance energy transfer (FRET). To improve sensitivity of the biosensor, HWRGWVC heptapeptide (HWR) was utilized to capture the antibody Fc portion via specific interaction to realize site-oriented immobilization. After connecting with ABEI-Ft@Au via Au-S bonding, HWR improved the incubation efficiency of the antibody with a better maintained biological activity. Under optimal conditions, the proposed biosensor provided a quantitative readout to PCT concentration in the range of 100 fg/mL to 50 ng/mL with a detection limit of 41 fg/mL. With favorable specificity, stability, and reproducibility, this highly efficient ECL-NSET system will inspire more interest in nanometal-based ECL quenching mechanism studies and development of new methods for site-oriented antibody immobilization to improve sensitivity.