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

Abstract

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 1×10−15 M and 1×10−18 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 1012 and 1015, 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.