Surface enhanced Raman scattering with gold nanoparticles: effect of particle shape

Abstract

The dependence of the Surface Enhanced Raman Scattering (SERS) by gold nanoparticles on their shape is examined using the organic dye, rhodamine 6G (R6G) as probe molecule. SERS has been explored extensively for applications in sensing and imaging, but the design and optimisation of efficient substrates is still challenging. In order to understand and optimise the SERS process in nanoparticles, gold nanospheres and their aggregates, nanotriangles, and nanostars of similar dimensions were synthesised and characterised according to their average size, zeta potential and UV/visible absorption. SERS from R6G was negligible for unaggregated nanospheres at 532 nm, close to the maximum of the surface plasmon resonance (SPR) at 560 nm. Upon aggregation of the nanospheres, the SPR shifts to ~660 nm, attributable to local surface plasmon "hotspots" between the spheres, and the SERS signal of R6G is significantly increased, at 785 nm. In monodisperse gold nanotriangles, the SPR is located at ~800 nm, and significant SERS of R6G is observed using 785 nm as source, as is the case for gold nanostars, which exhibit a double SPR with maxima at ~600 nm and ~785 nm, attributable to the core sphere and vertices of the structures, respectively. In suspensions of equal nanoparticle and dye concentration, the SERS effect increases as nanospheres<nanosphere aggregates <nanotriangles<nanostars, clearly indicating that control over the number of local field hotspots can optimise the SERS efficiency. Notably, it is demonstrated that the SERS intensity per nanoparticle scales with the magnitude of the SPR absorbance at the excitation wavelength (785 nm), providing a clear guide to optimisation of the process experimentally.

Gold nanostars for efficient in vitro and in vivo real-time SERS detection and drug delivery via plasmonic-tunable Raman/FTIR imaging

“…13,37 Thus, gold nanostars are unique materials with an intense surface plasmon band that affords absorption in the near-infrared region. [21][22][23][24][25][26] with MTX-nanostars during 48 hours of incubation using the Perkin Elmer Spotlight 400 system for the FTIR and the LabRAM HR Evolution spectrometer for the SERS maps.…”

“…The stability of the gold nanostars solution was tested for up to one month in 4ºC according to proceed. 13 The diameter, Zeta Potential and Surface Plasmon Resonance peaks of the zeta potentials of the nanostars with and without MTX are depicted in Table 1.…”

“…Raman spectroscopy was performed with a HORIBA Jobin Yvon HR800 spectrometer with 532 nm, 632 nm, and 785 nm diode laser as source according to proceed. 13 Spectral data were collected using a 10× microscope objective over the range 400-1800 cm −1 with a 10 sec integration time. The detector used was a 16-bit dynamic range Peltier cooled CCD detector.…”

“…13 We found that it is necessary to optimize several conditions and physical properties of nanostars to visualize anticancer drugs inside cancer cells and organs.…”

Self-Assembled Plasmonic Pyramids from Anisotropic Nanoparticles for High-Efficient SERS

“…The enhancement factors, as calculated in accordance to the classical equation [2,34], were found to be 1.8 9 10 7 , 5.3 9 10 6 and 1.9 9 10 6 for RD, OH and NS pyramids, respectively (see Supplementary Information Part SIV for calculation). This trend can be explained according to the electromagnetic theory and lightning rod effect, in which building blocks with sharp features are expected to be able to support higher electromagnetic field intensities due to the concentrated electromagnetic field within the regions of curvature [46,47]. This can be observed experimentally when comparing to the surface morphologies of each building block.…”