Ultra-high Sensitivity Surface-Enhanced Raman Spectroscopy (SERS) Substrates Based on Au Nanostructured Hollow Octahedra

Current standard tissue biopsy methods detect abnormal cells in an advanced stage mainly due to its inherent limitation of low-resolution and low-sensitivity. Under this context, plasmonic nanostructures are emerging as an alternative to current diagnostic methods because they are fast, accurate and with spatial resolution. In this work, through a facile, low-cost, reproducible and fast method, ultra-high sensitive reusable SERS substrates based on Au macroscale nanoassemblies with topographical features extending into three dimensions are developed from electrodeposited Ag octahedral structures via galvanic replacement reaction (GRR) onto ITO substrates. These materials are tested by impregnation of Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) as analytes to verify their effectiveness as ultra-high sensitivity SERS substrates with high spatial resolution. Amazingly, high resolution SERS spectra are still detected from R6G and 4-ATP solutions with concentrations as low as 1x10(-15) M and 1x10(-18) M respectively; which, to the best of our knowledge, are the lowest analyte concentrations detected by a SERS octahedra-based substrate to date. Furthermore, the corresponding enhancement factors (EF) of the SERS substrates are estimated to be approximately 10(12) and 10(15), which demonstrates their ultra-high sensitivity. Such results are theoretically confirmed via the discrete dipole approximation (DDA) combined with Mie's theory by determining the polarizability, as well as the intensities of the inner and outer main electric fields of many polarizable Au nanospheres which constitute the nanostructured hollow octahedron, and predicted results match quite well. Likewise, finite element modeling (FEM) visually demonstrates that hollow structures present better surficial electric field detection performance than solid ones.

Automated summary

In this study, a highly sensitive and reusable plasmonic nanostructure substrate was developed using a facile and low-cost method. The substrate exhibits high spatial resolution and is capable of detecting high-resolution SERS spectra at very low solution concentrations. The results were confirmed using the discrete dipole approximation and Mie's theory, and finite element modeling demonstrated the superior surface electric field detection performance of hollow structures compared to solid structures.