Quasi-fractal Gold Nanoparticles for Sers: Effect of Nanoparticle Morphology and Concentration

Abstract

<p>Quasi-fractal gold nanoparticles can be synthesized via a modified and temperature controlled procedure initially used for the synthesis of star-like gold nanoparticles. The surface features of nanoparticles leads to improved enhancement of Raman scattering intensity of analyte molecules due to the increased number of sharp surface features possessing numerous localized surface plasmon resonances (LSPR). The LSPR is affected by the size and shape of surface features as well as inter-nanoparticle interactions, as these affect the oscillation modes of electrons on the nanoparticle surfaces. The effect of the particle morphologies on the LSPR and further on the surface-enhancing capabilities of these nanoparticles is explored by comparing different nanoparticle morphologies and concentrations. We show that in a fixed nanoparticle concentration regime, Quasi-fractal gold nanoparticles provide the highest level of surface enhancement, whereas spherical nanoparticles provide the largest enhancement in a fixed gold concentration regime. The presence of highly branched features enables these nanoparticles to couple with a laser wavelength despite having no strong absorption band and hence no single surface plasmon resonance. This cumulative LSPR may allow these nanoparticle to be used in a variety of applications where laser wavelength flexibility is beneficial, such as in medical imaging applications where fluorescence at short laser wavelengths may be coupled with non-fluorescing long laser wavelengths for molecular sensing. </p>

Synthesis of anisotropic Au–Cu alloy nanostructures and its application in SERS for detection of methylene blue

“…This observation suggests that they act as potential SERS substrate for detecting MB. The alloys A0911 and A1821 have similar multiply twinned branched shape morphology with sharp edges and corners that allows for the strong coupling of laser electromagnetic field leading to enhancement of MB signal via SERS effect [41,42,44]. Additionally, these samples show an additional LSPR peak centred at λ max ∼800 nm as discussed in UV-vis section (cf see figure 9).…”

“…In contrast to previous findings where Au NPs are known to be SERS active, we attribute the absence of SERS effect in A0910 to two major factors: first, as can be seen from the TEM images (cf figure 4(a)) that the Au NPs are spherical and mono-dispersed with no tell-tale signs of agglomeration. The SERS activity of metal NPs are mainly contributed by the presence of rough surfaces and edges in nanoparticle as well as NPs clusters which act as hotspots for the enhancement of Raman signal [41,42]. The synthesized Au NP in this work lacks all of these features which manifests itself into a SERS inactive substrate at a concentration of 1 μM of MB.…”