Highly sensitive SERS-based immunoassay with simultaneous utilization of self-assembled substrates of gold nanostars and aggregates of gold nanostars

We have developed a highly sensitive SERS-based sandwich immunoassay by utilizing two derivatives of gold nanostars simultaneously. One is densely packed self-assembled substrates of gold nanostars and the other is labeled immune nanostar aggregates. Taking advantage of the electromagnetic field coupling between tips of adjacent individual nanostars, the self-assembled substrate of gold nanostars exhibited a better SERS performance than that of gold nanoparticles. On the other hand, the immuno-aggregates made of gold stars also showed an improved SERS activity compared to those made of gold nanoparticles. Thus, by combining the self-assembled substrates of gold nanostars and immuno-aggregates of gold nanostars, highly sensitive sandwich immunoassays were obtained. The experimental results show that there existed a linear correlation between the concentration of antigens and the prominent peak intensity of SERS signals. The limit of detection (LOD) is similar to 10 fg mL(-1), 5 to 6 orders smaller than that of the conventional ELISA protocols. Such a structure will have potential wide-range applications in biological sensing and quantitative biochemical analysis.