Synthesis and Analysis of Thiol-Stabilized Gold Nanoparticles

Samuel Blass, Department of Physics and Department of Biology, Yeshiva College, Yeshiva Univer Malka R Bromberg, Department of Physics, Stern College for Women, Yeshiva University, New York, NY Frieda Dukesz, Department of Physics, Stern College for Women, Yeshiva University, New York, NY Qi Wang, Department of Physics, Stern College for Women, Yeshiva University, New York, NY Anatoly I Frenkel, Department of Physics, Stern College for Women, Yeshiva University, New York, NY Neer Asherie, Department of Physics and Department of Biology, Yeshiva College, Yeshiva Univer Miriam H Refailovich, Department of Materials Science and Engineering, SUNY Stony Brook, NY 11794, USA Yuan Sun, Department of Materials Science and Engineering, SUNY Stony Brook, NY 11794, USA Joo Kang, Materials Research Laboratory, University of Illinois, Urbana, IL 61801, USA

Abstract Investigation of nanoparticles attracts much attention since they have non-bulk properties and give rise to many emerging applications. For example, they are used as catalysts, bio-, photo- and chemical sensors and as energy storage materials. Hydrophilic particles in particular can be used for biological applications, such as drug delivery, protein sensors, or enhancers of bioimaging methods such as MRI or PET. For a better understanding of their functions and reaction mechanisms, structural studies of nanoparticles are required. This can best be done if synthesized nanoparticles are similar to one another, since particles of different sizes have different properties. The aim of this research was to determine the synthesis parameters that allow us to control the size and variation in size of both toluene- and water- soluble alkanethiol-stablized gold nanoparticles. A variety of methods were used to accurately determine the sizes of the nanoparticles since each method is sensitive to different aspects of nanoparticles. The results were compared to determine the complementary properties of the particles. Two types of nanoparticles were produced. Toluene-soluble nanoparticles were made using a two-phase method and water-soluble nanoparticles were synthesized using a one-phase method. Water-soluble nanoparticles were made since using water as a dispersal media increases the number of available techniques for analysis of the effective particle sizes. In both methods, the average size of the nanoparticle was adjusted by varying the molar ratio of gold and thiols. Additionally, we varied the thiol chain length as well to investigate its effect on the cluster structure. Four different methods were used to determine the sizes of the nanoparticles. (i) Transmission Electron Microscopy (TEM) studies were carried out at Stony Brook University. This technique is mostly sensitive to the combined radius of the gold core and surface sulfur atoms. (ii) Extended X-ray Absorption Fine Structure (EXAFS) was performed at Brookhaven National Laboratory. In this technique photon absorption was measured as a function of energy and further processed to calculate the metal-metal and metal-ligand coordination numbers, inter-atomic distances, and finally, the metal core radii. (iii) Quasi-elastic light scattering (QLS) was used to calculate the hydrodynamic radii of the nanoparticles which includes both the metal core and the thiol chain; (iv) Optical Extinction Spectroscopy (UV-Vis) provided a consistency check for the radii of the metal cores. We found general agreement between all four techniques. As expected, the TEM measurements were consistently larger than the corresponding EXAFS data. The QLS measurements showed a wide distribution of sizes of small particles, and also revealed the presence of larger aggregates.

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