In this paper, we demonstrate the synthesis of monodispersed silver nanoparticles (NPs) of controlled size (20.5 ± 3.3 nm) in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing-capping agent. We then coat these NPs in a layer of gold with controllable thickness through a reduction-deposition process. The materials are characterized using several techniques including high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The results show that we were able to synthesize not only monodispersed Ag NPs but also core-shell Ag-Au NPs with a discrete structure, which is significant because of the challenges associated with the creation of such materials, namely the propensity of metallic Ag to be oxidized by the presence of ionic Au. The NPs are of interest for use in a wide range of potential applications, including biomedical diagnostics and biomolecular detection as well as many others.

In this paper, we study the relationship between nanoparticles’ structure/composition and the chemical nature of the molecules to be identified in surface enhanced Raman scattering (SERS) spectroscopy. Three types of nanoparticles (NPs) were synthesized, including Ag, Au, and silver coated by gold (Ag@Au), in order to study the resulting enhancement effects. When a rhodamine 6G dye molecule was used to assemble the NPs, it was found that Ag NPs exhibited the highest enhancement activity. However, when a thiol containing 3-amino-1,2,4-triazole-5-thiol molecule was used to assemble the NPs, it was found that the Ag@Au NPs exhibited high Raman activity as well as the Ag NPs. The results give insight into how the chemical properties of the molecules to be analyzed play an important role in the SERS detection. An additional parameter of the analysis reveals the relative stability of the three types of NP probes synthesized with regard to oxidation in the presence of different mediating molecules and varying salt concentrations. The results are of interest in designing and employing NP probes to detect biological molecules using colorimetric and SERS based approaches.

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This paper reports a qualitative comparison between the optical properties of a set of silver core, gold shell nanoparticles with varying composition and structure to those calculated using the Mie solution. To achieve this, silver nanoparticles were synthesized in aqueous phase from a silver hydroxide precursor with sodium acrylate as dual reducing-capping agent. The particles were then coated with a layer of gold with controllable thickness through a reduction-deposition process. The resulting nanoparticles reveal well defined optical properties that make them suitable for comparison to ideal calculated results using the Mie solution. The discussion focuses on the correlation between the synthesized core shell nanoparticles with varying Au shell thickness and the Mie solution results in terms of the optical properties. The results give insight in how to design and synthesize silver core, gold shell nanoparticles with controllable optical properties (e.g., SPR band in terms of intensity and position), and has implications in creating nanoparticle materials to be used as biological probes and sensing elements.

Silver nanoparticles coated by a layer of gold (Ag@Au) have received much attention because of their potential application as ultra sensitive probes for the detection of biologically important molecules such as DNA, proteins, amino acids and many others. However, the ability to control the size, shape, and monodispersity of the Ag@Au structure has met with limited success. In our own research we have addressed this challenge by creating an aqueous wet chemical synthesis technique towards size and shape controllable Ag@Au nanoparticles. These materials are highly interesting because of the tunable silver core size, and the tunable gold shell thickness, opening many avenues to the modification of the particle properties in terms of bio-molecular sensing. The resulting nanoparticle probes were functionalized with two complementary stranded DNA oligonucleotides. When combined, the complementary strands hybridized, causing the Ag@Au nanoparticles to assemble into large nano-structures. The presence of the oligonucleotide was confirmed through a series of techniques including UV-Vis and RAMAN spectroscopy, as well as HR-TEM, XPS, DLS, and many others. The results reflect the role that the nanoparticle physical properties play in the detection of the bio-molecules, as well as elucidate the characteristics of the bio-molecule/nanoparticle interaction.