A sensitive SPR biosensor based on hollow gold nanospheres and improved sandwich assay with PDA-Ag@Fe₃O₄/rGO

A novel surface plasmon resonance (SPR) biosensor based on hollow gold nanospheres (HGNPs) and an improved sandwich assay was developed to detect rabbit IgG. The electromagnetic coupling between the HGNPs and Au film, and the notable plasmonic fields spread over the inner and outer surfaces of HGNPs, led to the considerable amplification of the SPR signal. Polydopamine-Ag@Fe₃O₄/reduced graphene oxide (PDA-Ag@Fe₃O₄/rGO) was introduced to bind detection antibody (Ab₂) to form the improved sandwich structure. Ag nanoparticles were excited to produce SPR and their hot electrons were doped on graphene thin films, which amplified the response of biomolecules. Magnetic nanoparticles (Fe₃O₄) simplified the collection of Ab₂-PDA-Ag@Fe₃O₄/rGO. An external layer of polydopamine (PDA) permitted the efficient immobilization of Ab₂ without activation via abundant functional groups and protected the nanoparticles from etching or agglomeration. In addition, because of its large mass, Ab₂-PDA-Ag@Fe₃O₄/rGO also played a key role in the further amplification of the SPR response signals. This novel SPR biosensor exhibited an effective response to the rabbit IgG at the different concentrations ranging from 0.019 to 40.00μgmL^-1. This value is 132 times lower than that observed for a traditional SPR biosensor based on Au-3-mercaptopropionic acid and 8 times lower than that obtained from an Ab₂ sandwich assay, which indicates that the SPR sensor has high sensitivity. In addition, the designed biosensor showed satisfactory recoveries to detect the rabbit IgG spiked in serum samples. Therefore, the novel SPR biosensor with high sensitivity and acceptable recovery has potential for practical applications.