Label-free immunosensors based on a novel multi-amplification signal strategy of TiO 2 -NGO/Au@Pd hetero-nanostructures.

A label-free electrochemical immunosensor for quantitative detection of human epididymis specific protein 4 antigen (HE4 Ag) was developed by a novel multi-amplification signal system. The multi-amplification signal system was formed by loading bimetallic Au@Pd holothurian-shaped nanoparticles (Au@Pd HSs) on titanium oxide nanoclusters functionalized nitrogen-doped reduced graphene oxide (TiO2-NGO). The Au@Pd HSs were obtained via seed-mediated approach with in-situ grown palladium nanoarms on gold nanorods (Au NRs) surfaces, which possessed good electrocatalysis for hydrogen peroxide (H2O2) reduction and excellent biocompatibility. The TiO2-NGO with the high catalytic activity and large specific surface area was synthesized by hydrothermal method. Using H2O2 as an electrochemically active substrate, the prepared label-free electrochemical immunosensor based on the TiO2-NGO/Au@Pd HSs hetero-nanostructures as the signal amplification platform exhibited excellent selectivity, reproducibility and stability for the detection of HE4 Ag. Meanwhile, the linear range from 40 fM to 60 nM with the detection limit of 13.33 fM (S/N = 3) was obtained, indicating the immunosensor offers a promising method for clinical detection of HE4 Ag.