Dual nanoparticle amplified surface plasmon resonance detection of thrombin at subattomolar concentrations

A novel dual nanoparticle amplification approach is introduced for the enhanced surface plasmon resonance (SPR) detection of a target protein at subattomolar concentrations. Thrombin was used as a model target protein as part of a sandwich assay involving an antithrombin (anti-Th) modified SPR chip surface and a thrombin specific DNA aptamer (Th-aptamer) whose sequence also includes a polyadenine (A₃₀) tail. Dual nanoparticle (NP) enhancement was achieved with the controlled hybridization adsorption of first polythymine-NP conjugates (T₂₀-NPs) followed by polyadenine-NPs (A₃₀-NPs). Two different nanoparticle shapes (nanorod and quasi-spherical) were explored resulting in four different NP pair combinations being directly compared. It was found that both the order and NP shape were important in optimizing the assay performance. The use of real-time SPR measurements to detect target concentrations as low as 0.1 aM is a 10-fold improvement compared to single NP-enhanced SPR detection methods.