Nanostars on a fiber facet with near field enhancement for surface-enhanced Raman scattering detection

A 4-pointed gold nanostar is proposed to form the array on a fiber facet to achieve a greatly enhanced near field intensity for Surface-Enhanced Raman Scattering (SERS) detection. The proposed gold nanostar array has a Surface Plasmon Resonance (SPR) peaked at a wavelength of ∼650 nm with up to 45 times electric field intensity enhancement compared with the state-of-the-art nanorod design. It has a wideband SPR field enhancement spanned from 600 to 720 nm, which covers the wavelengths for both the excitation light (632.8 nm) and the Raman signal of the analytes (675–706 nm); With symmetrical structure it forms four hot spots in every unit cell and can detect best for light polarized horizontal or perpendicular to the waist of the nanostars. It also could be altered to tune the SPR and allows the fiber sensor to resonate at different wavelengths, as demonstrated by an example at 533 nm. All the above features make the gold nanostar-based compact and portable fiber sensor an attractive solution for SERS detection.