The sensitivity of lateral flow assays (LFA) was increased 30-fold by making use of spherical core-shell gold-silica nanoparticles (AuNP@SiO2 NPs). They can be prepared by silylation of surfactant stabilized AuNPs. The AuNP@SiO2 NPs are highly stable and can be used to label antibodies at virtually any concentration. The detection limit of an LFA for alpha-fetoprotein (AFP) can be decreased from 10 ng·mL-1 to 300 pg·mL-1 which makes it comparable to an enzyme-linked immunosorbent assay. To demonstrate the applicability to an immunoassay, a sandwich assay was developed for vanillin by covalent modification of the AuNP@SiO2 NPs with antibody. By using the method, vanillin can be detected visually in milk powder samples in concentrations as low as 100 ng·g-1. With unique optical property and great stability, this AuNP@SiO2 endows great potential in biosensing applications. Graphical abstract Controlled growth of AuNP@SiO2. The newly prepared AuNP has a negative hydration layer. This layer is further surrounded by a bilayer of CTAB through electrostatic attraction. The hydrophobic inner layer enables the access and assembling of APTES and MTTS. After the hydrolysis of siloxane, a thin layer of silica shell is formed around AuNP.
Keywords: AFP; Core-shell gold nanoparticle; Lateral flow assay; Vanillin.