Abstract
This work describes a surface plasmon resonance (SPR) based sandwich immunoassay for the cardiac biomarker troponin I (cTropI). A thin film of polydopamine (PDA) was deposited on a gold chip modified with hollow gold nanoparticles (HGNPs) via self-polymerization of DA, and this allows for the direct immobilization of anti-cTropI. cTropI and anti-cTropI (as the secondary antibody) were sequentially introduced to the system to form a sandwich structure on the surface of the sensor. The HGNPs are found to strongly enhance the SPR signal, and the PDA layer acts as a viable support for immobilization of the antibody compared to that of conventional 3-mercaptopropinic acid (MPA) and does not require chemical activation. The PDA film also protects the HGNPs from agglomeration. The enhancement in the SPR signal is found to be proportional to the concentration of cTropI in the range from 1.25 to 40 μg mL−1. The detection limit is 38 ng mL−1, which is 67 times lower than that of an SPR biosensor based on the use of gold-MPA. The assay was applied to the determination of cTropI spiked in serum samples, and the recoveries were satisfactory.
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