Scattering Correlation Spectroscopy and Raman Spectroscopy of Thiophenol on Gold Nanoparticles: Comparative Study between Nanospheres and Nanourchins

Abstract

The surface characterization of branched and spherical gold nanoparticles was done by two complementary techniques: scattering correlation spectroscopy (SCS) and surface-enhanced Raman spectroscopy (SERS). Thiophenol was used as a surface marker to probe the surface area and the gold–thiophenol interaction in gold nanourchins (GNUs) and gold nanospheres (GNSs). We observed that, for GNU, the thiophenol is first grafted on the core, with a saturation concentration of about 10–3 M as observed for GNSs. Afterward, the saturation of the branches occurs at a higher thiophenol concentration (∼1 M). A numerical calculation of the surface areas of GNSs of different sizes allowed for the estimation of the GNU surface area. The hydrodynamic radius was measured at different steps of thiophenol–GNP functionalization. By comparing spherical and nonspherical nanoparticles, we demonstrate that the molecule–GNP interaction is highly dependent on the nanoparticle morphology (size and shape).

Nanostructured Assemblies of Gold and Silver Nanoparticles for Plasmon Enhanced Spectroscopy Using Living Biotemplates

“…Raman spectroscopy is an analytical technique commonly used in biomedical applications. Over the years, a wide variety of molecular targets have been investigated by SERS using active nanoparticles, mainly gold and silver [2,3,11,12,[26][27][28][29][30][31][32][33][34]. The plasmonic origin of the phenomenon is fully understood [19,37], and nowadays the major effort focuses on the fabrication of new substrates for SERS [38].…”

“…As discussed previously (Figures 2 and 3), the FG and FGS surfaces clearly offer the necessary morphological characteristics of a typical SERS substrate. To evaluate their potential as sensors or biosensors via surface-enhanced Raman scattering, small amounts of thiophenol were used directly on FG (Figure 4a) and FGS (Figure 4b) microtubules [32,33,[39][40][41].…”

“…Thiophenol has been widely used as a molecular probe to determine the suitability of substrates for SERS and to estimate an enhancement factor due to the affinity of the thiol group (R-SH) toward noble metal surfaces [32,33]. Generally, its adsorption on gold or silver proceeds by releasing hydrogen after breaking the thiol bond.…”

“…Using the same conditions, the spectrum of the substrate that supported the microtubules was used as a control to determine the enhancement factor of the FGS substrate for the thiophenol molecules [31,32]. The control spectrum was taken with laser powers of 1.2 mW and 2.5 mW to obtain a substantial signal of the Raman scattering of thiophenol.…”

“…Several techniques allow tuning the characteristics of surfaces for SERS, for instance through lithographic methods, precipitation from colloidal suspensions, or by the physical vapor deposition of metals on a nanostructured surface of silicon or ZnO [27]. Anisotropic metal nanoparticles, on the other hand, offer the possibility of creating "hotspots" of enhanced activity [26,[28][29][30][31][32][33].…”