Unique gold sponges: biopolymer-assisted hydrothermal synthesis and potential application as surface-enhanced Raman scattering substrates

In this paper we describe a biopolymer-assisted hydrothermal approach to the synthesis of gold sponges. This is carried out by transferring a hyaluronic acid potassium salt/HAuCl4 aqueous solution into a stainless steel autoclave with a Teflon liner and heating in an oven at 180 degrees C for 6 h. Here, hyaluronic acid potassium salt plays three roles in the synthesis, namely, stabilization, reduction, and as a soft template. Field emission scanning electron microscopy images, energy-dispersive x-ray spectroscopy, and x-ray diffraction reveal that the materials obtained consist of an interconnected framework of face-centred cubic metallic gold filaments, which is approximately 0.6 mu m in width and composed of fused micrometre-sized particles that enclose pores 1-4 mu m in size. The test of surface-enhanced Raman scattering (SERS) from 4-mercaptobenzoic acid shows that the prepared gold sponges are an active SERS substrate. This is largely because they had an increased number of particle junctions, which are SERS active sites. This route can also be extended to the fabrication of silver sponges, which are composed of fused crystallites with diameters of 200-400 nm that enclosed pores 0.4-2 mu m in size. The test of SERS from Rhodamine 6G also reveals that the prepared silver sponges are likewise an excellent SERS substrate.