| Gold nanoparticles (GNPs) attract great scientific and technological interest because of their attractive size (shape) related electronic, magnetic, catalytic and optical properties and important applications in catalysis, photonic devices, and sensors.. Most recently, emphasis has been placed on organizing or assembling gold nanoparticles into one-, two-, and three-dimensional superstructures. This is due to that such superstructures can display rich optical and electrical characteristics that are distinctly different from individual nanoparticles. Therefore, some intriguing approaches have been explored for the design and fabrication of such gold porous nanostructures. These studies will provide important theoretical basis for the preparation of gold nanomaterials, multi-dimensional assembly and applications. In our work, we demonstrate facile self-assemble procedures to prepare multi-dimensionally gold/Glu nanocomposites with gold nanoparticles serving as building blocks by adjusting environmental factors. Furthermore, the properties and function of the obtained gold nanoparticles and gold aggregates have been investigated.1. Br-Induced Facile Fabrication of Sponge-like gold/amino acid Nanocomposites and Their Applications in Surface-Enhanced Raman ScatteringWe use a facile method for the fabrication of spongelike gold/amino acid nanocomposites by the addition of NaBr to glutamic acid-stabilized gold nanoparticles (GNPs) at room temperature. The gold/glutamic acid (Glu) nanocomposite is characterized by TEM, SEM, UV-vis spectroscopy, and XRD measurements. The results suggest that the three-dimensional spongelike gold/Glu nanocomposites with mean diameter of50nm are formed via the nanospheres fusing into one another. The driving force for the fabrication of spongelike gold/amino acid nanocomposites is the van der Wals attractive forces of Br partially coated GNPs. Furthermore, the obtained spongelike gold nanocomposites can be used as surface-enhanced Raman scattering (SERS) substrates with high SERS activity and stability for detecting Rhodamine6G (R6G) molecules. Hence, NaBr-mediated preparation of SERS substrates described in this work has potential applications in chemical and biological analysis as well as medical detection.2. pH-induced Self-assembly of Amino Acid Stabilized Gold Nanoparticles and their applicationTriggered by pH changes, glutamic acid stabilized gold nanoparticles can self-assemble into one-, two-, and three-dimensional (1D,2D, and3D) superstructures. The obtained gold superstructures were characterized by TEM, SEM, UV-visible spectroscopy, EDS and XRD measurements. The results suggest that the multidimensional network superstructures are formed via the nanospheres fusing into one another. The main driving force for the fabrication of these superstructures is the attractive (cross-linking) force, provided by glutamic acid molecules. Interestingly, disassembly of the pH induced gold superstructures is hardly performed by increasing pH or temperature, but can be performed by the addition of small amount of NaBr. In addition, the pH induced superstructures exhibit higher surface enhancement than pure gold nanoparticles when two analytes Rhodamine6G and4-mercaptopyridine were used as molecule probes3. Facile Synthesis of Casein Micelles Stabilized Gold Nanoparticles with High Catalytic Activity and Fluorescent PropertyMonodisperse casein micelle stabilized-gold nanoparticles (Au NPs) which are eco-friendly and biocompatible, were synthesized in aqueous medium by chemical reduction of HAuCl4with NaBH4in the presence of amphiphilic protein aggregates, casein micelles. The prepared Au NPs were evidenced by UV-vis spectroscopy, transmission electron microscopy (TEM), and XRD analysis. The size of the monodisperse Au nanoparticle can be controlled easily by adjusting casein concentration, and the environment pH in the system. Furthermore, casein micelle stabilized Au nanoparticles functions as effective catalyst to activate the reduction of4-nitrophenol (to form4-aminophenol) in the presence of NaBH4. On the basis of their excellent colloidal stability and catalytic function, and biocompatible, the casein micelle-stabilized Au NPs hold great promise for being used in nanoscience and biomedical applications.Highly stable, water-soluble Au nanoclusters have been successfully prepared in aqueous medium by chemical reduction of HAuCl4with NaBH4in the presence of amphiphilic protein aggregates, casein micelles. The optical and fluorescence properties of the Au nanoclusters can be easily controlled by varying the synthetic conditions, such as experimental pH, casein concentration, and the added NaX. These easily prepared, water-soluble, and high quantum yield gold nanodots lend insight into the molecular nature of small metal nanoclusters and may find application as novel biocompatible fluorophores. |
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