The proposed sandwich model was based on the common sandwich
format assay of the ELISA. We used PtNPs to replace enzymes
so that the detection signal was amplified. In the sandwich format
assay, IgGs (1st Ab) were immobilized on the slide as the first
layer for binding sample antigens (protein A). Then various concentrations
of protein A were immobilized on the IgG coating layer
as the second layer. Finally, the corresponding IgG–PtNPs conjugates
were added, and these were responsible for producing and
amplifying the optical detection signal