Gold Nanorods Performing as Dual-Modal Nanoprobes via Metal-Enhanced Fluorescence (MEF) and Surface-Enhanced Raman Scattering (SERS)

The integration of metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS) onto single plasmonic nanoparticles is highly desirable to boost up accuracy and sensitivity in spectroscopic investigations. In this work, we demonstrate the feasibility of performing both MEF and SERS analysis on gold nanorods (GNRs) decorated with a unique molecular probe, here Rose Bengal (RB) fluorophore. While the cetyltrimethylammonium bromide layer on GNRs captures RB molecules preventing fluorescence quenching, the selective excitation of the two surface plasmon resonances of GNRs can trigger either the enhancement of fluorescence emission or Raman scattering. Both fluorescence enhancement mechanisms, i.e. increase of excitation rate and increase of quantum efficiency, promote an average 2.2-fold enhancement. For excitation with 785 nm laser line an average SERS enhancement of 1.7 × 105 is estimated and compared with the electromagnetic enhancement provided by finite-difference time-domain (FDTD) simulations. An extended dual-modal response of RB–GNRs conjugate is demonstrated by resonant excitation of both RB and GNRs with 532 nm laser line, which allows the surface-enhanced resonance Raman scattering (SERRS) and MEF signals to be detected simultaneously. The reporting abilities in SERS are demonstrated by conveying the Raman fingerprints of two molecular species concomitantly adsorbed on the surface of GNRs.