Three-dimensional ordered Ag/ZnO/Si hierarchical nanoflower arrays for spatially uniform and ultrasensitive SERS detection

Surface-enhanced Raman scattering (SERS) is a powerful analytic tool that can provide information of molecular structures and composition of analyzes. The application of SEAS for ultrasensitive detection of chemical and biological molecules has attracted particular interests in recent years. Here, a novel type of three-dimensional SEAS substrate with uniform hierarchical nanoflower structures was fabricated by growing dense ZnO nanowires (ZnO NWs) on ordered vertically aligned Si nanorods (Si NRs) through a chemical hydrothermal (HT) method. After being decorated with Ag nanoparticles (Ag NPs), such branched nanostructure exhibits greatly improved SEAS signals with a detection limit of Rhodamine 6 G (R6 G) down to 1 pM and an excellent uniformity (relative standard deviation lowered to about 6%). Furthermore, this SERS-active substrate is successfully applied to investigate the aggregation status of human islet amyloid polypeptides (hIAPP). The structural change of amyloid aggregates can be detected from SEAS spectra at a single aggregate level, providing useful information for the prevention and treatment of protein conformation diseases. Therefore, our studies not only demonstrate a promising type of SEAS substrates for highly uniform, reproducible and ultrasensitive molecular detection, but also suggest a potential method for label-free detection on conformation change of amyloid peptides in aggregation process.