Study on the roughen process of branches of AuAg nanostars for the improved surface-enhanced Raman scattering (SERS) to detect crystal violet in fish

The techniques used to precisely tune the morphologies of noble metal nanoparticles are of vital importance as complex three-dimensional nanostructures can generate many "hot spots" for Surface-enhanced Raman Scattering (SERS). Especially, the SERS properties of star-shaped nanoparticles are closely related to the position, number and morphology of branches, making the control over the final morphology of them more important. By adding different reducing agents during the growth process of AuAg nanostars, we accurately controlled the morphology of branches, and synthesized three kinds of hyperbranched star-shaped nanostructures: Lamellar nanostars, Sea urchin-shaped nanostars and Serrated nanostars. The SERS performance of the hyperbranched nanostars were all stronger than that of common AuAg nanostars. Among them, Lamellar nanostars gained the best SERS enhanced factor about 1 x 107 due to the built-in nanogaps and sharp edges. The SERS detection probes prepared with purified Lamellar nanostars had high uniformity and stability, and showed excellent sensitivity in detecting crystal violet in fish, with detection range of 0.01-10 nM and detection limit of 0.015 nM. The results of this work not only provide guidance for the construction of complex Au and Ag bimetallic nanostructures, but also supply a superior material to develop highly sensitive optical chemical sensors and biosensors.