Focused ion beam-fabricated Au micro/nanostructures used as a surface enhancedRaman scattering-active substrate for trace detection of molecules and influenzavirus

Abstract

The focused ion beam (FIB) technique was used to precisely fabricate patterned Aumicro/nanostructures (fibAu). The effects of surface enhanced Raman scattering (SERS)on the fibAu samples were investigated by adjusting the geometrical, dimensional, andspacing factors. The SERS mechanism was evaluated using low-concentrationrhodamine 6G (R6G) molecules, physically adsorbed or suspended on/within themicro/nanostructures. The results indicated that for detecting R6G molecules, hexagon-likemicro/nanostructures induced a higher electromagnetic mechanism (EM) due to theavailability of multiple edges and small curvature. By decreasing the dimensions from 300to 150 nm, the laser-focused area contained an increasing number of micro/nanostructuresand therefore intensified the excitation of SERS signals. Moreover, with an optimizedgeometry and dimensions of the micro/nanostructures, the relative intensity/surface areavalue reached a maximum as the spacing was 22 nm. An exponential decrease was found asthe spacing was increased, which most probably resulted from the loss of EM. The spacingbetween the micro/nanostructures upon the fibAu was consequently regarded as thedominant factor for the detection of R6G molecules. By taking an optimized fibAu todetect low-concentration influenza virus, the amino acids from the outermostsurface of the virus can be well distinguished through the SERS mechanism.