Polydopamine-Functionalization of Graphene Oxide to Enable Dual Signal Amplification\nfor Sensitive Surface Plasmon Resonance Imaging Detection of Biomarker

Abstract

Surface\nplasmon resonance imaging (SPRi) is one of the powerful\ntools for immunoassays with advantages of label-free, real-time, and\nhigh-throughput; however, it often suffers from limited sensitivity.\nHerein we report a dual signal amplification strategy utilizing polydopamine\n(PDA) functionalization of reduced graphene oxide (PDA-rGO) nanosheets\nfor sensitive SPRi immunoassay in serum. The PDA-rGO nanosheet is\nsynthesized by oxidative polymerization of dopamine in a gentle alkaline\nsolution in the presence of graphene oxide (GO) sheets and then is\nantibody-conjugated via a spontaneous reaction between the protein\nand the PDA component. In the dual amplification mode, the first signal\ncomes from capture of the antibody-conjugated PDA-rGO to form sandwiched\nimmunocomplexes on the SPRi chip, followed by a PDA-induced spontaneous\ngold reductive deposition on PDA-rGO to further enhance the SPRi signal.\nThe detection limit as low as 500 pg mL^–1 is achieved\non a nonfouling SPRi chip with high specificity and a wide dynamic\nrange for a model biomarker, carcinoembryonic antigen (CEA) in 10%\nhuman serum.