Synthesis of Size and Shape Controlled Silver Nanoparticles Coated by a Thin Layer of Gold and Their Use as Ultrasensitive Biomolecular Probes

Abstract

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.

Noble Metal Nanostructures Influence of Structure and Environment on Their Optical Properties

“…Significant color change from yellow-amber to dark-amber to grey to grey-purple and finally to purple was observed during the Au deposition ( Figure 12). Great attention was paid to the shift of the SPR peak position of the forming particles in regard to the amount of the Au introduced [55]. Absorption spectrum of alloy nanoparticles prepared by laser irradiation of mixture of colloidal solutions of Ag and Au nanoparticles (prepared beforehand by laser ablation in liquid environment) was found not to be a simple combination of the Au and Ag colloid solution spectra (Figure 13).…”

“…UV-Vis spectra for Ag and Ag/Au particles prepared with increasing Au content, as-synthesized Ag nanoparticles (A), 5% Au (B), 15% Au (C), 25% Au (D)[55].…”