Abstract
The synthesis of gold nanoshells involves the preparation of precursor seed particles consisting of nanoparticulate gold loaded on a dielectric core as scaffolds on which the layer of gold shell can be grown. The common route in preparing these seed particles involves a two-step technique of synthesizing colloidal gold particles followed by attaching them to amine functionalized dielectric core. In this paper, we present the use of a singlestep deposition-precipitation (DP) process, commonly used in the catalytic field, as a feasible alternative route to seeding gold hydroxide nanoparticles onto a silica core and growing a layer of gold shell around the core without the need for prior synthesis of colloidal gold. The various factors such as pH, temperature and time of reaction, as well as the effect of amine functionalization of silica on the deposition of gold were investigated. Compared to bare silica nanoparticles whose low isoelectric point render the DP process of seeding nanoparticulate gold unfavorable, amine functionalization of the silica surface is able to alter its isoelectric point to facilitate the deposition of gold hydroxide nanoparticles and increase the uniformity and density of seeding. We have also established that by varying the pH and time of reaction, it is possible to control the size of the gold hydroxide nanoparticles and density of seeding. The highest seeding density was achieved at pH 8 where the surface charge on the amine terminated silica surface favored the attraction of complex gold anions and the hydrolysis of these complex anions at elevated temperature produced the insoluble gold hydroxide precipitate which was readily deposited on the silica. As the time of reaction was increased from 3 min to 60 min, these gold hydroxide nanoparticles also increased in size from 2 nm to 7 nm. We have also shown the progressive growth of the gold hydroxide seeds to eventually form gold nanoshells with a complete layer of gold shell with tunable optical response.
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James Chen Yong Kah is currently pursuing a PhD in Bioengineering in the National University of Singapore (NUS). He received his B.Eng. (Electrical) (1st Class Honors) with minors in Bioengineering and Management of IT from NUS. His current research is on the development of cancer targeting metallic nanostructures as optical probes for reflectance-based optical imaging, working jointly under the Colin Sheppard's bioimaging group in NUS and Malini Olivo's photodynamic therapy and optical imaging group in National Cancer Centre Singapore.
Nopphawan Phonthammachai is currently a Research Fellow at the School of Materials Science and Engineering, Nanyang Technological University, Singapore. Her research interests are the designing of new potential materials (apatite based-, functionalized-, comp-osite, nano-materials) and development of in-house metal oxide (TiO2, ZrO2, Fe2O3 etc.) using simple chemistry-based processes for catalytic, environmental and biological applications.
Rachel Cheng Yi Wan is an undergraduate from the School of Materials Science and Engineering, Nanyang Technological University, Singapore. She is assisting in this research work on the synthesis of gold nanoshells as part of her final year project.
Jing Song is an undergraduate from the School of Materials Science and Engineering, Nanyang Technological University, Singapore. She is assisting in this research work on the synthesis of gold nanoshells as part of her final year project.
Timothy White is currently Associate Professor at the School of Materials Science and Engineering and Director of the Facility for Advanced Characterisation, Testing & Simulation (FACTS). He has over twenty years of experience in the design and demonstration of advanced materials for environmental, superconducting, ionic conductivity and hydrogen storage applications. His particular interests lie in tailoring ceramics at the atomic scale to develop or enhance particular properties. These studies have been supported and facilitated through the use and deep knowledge of advanced characterization methods, including atomic resolution electron microscopy, crystal refinement using X-ray and neutron diffraction, and synchrotron-based surface analysis.
Subodh Mhaisalkar is an Associate Professor in the School of Materials Science & Engineering at the Nanyang Technological University (NTU), Singapore. He is also the Director of NTU Nanoscience & Nanotechnology Cluster and Head of Materials Technology Division. Subodh received his Bachelors' degree from IITBombay and his MS/PhD degrees from The Ohio State University. He has over 10 years of research and engineering experience in the Microelectronics industry where he held Engineering and R&D positions in ST Assembly & Test Services, National Semiconductor, and the Singapore Institute of Manufacturing Technology. His areas of expertise and research interests include Organic & Molecular Electronics, Nanobioelectronics including biosensors.
Iman Bte Ahmad graduated with a degree in B (Materials Eng.)(Hons) from Nanyang Technological University, Singapore. She worked for over a year as a Research Engineer for the National University of Singapore, focusing on techniques to fabricate gold-SiO2 nanostructures for optical imaging. She also developed atomically-flat gold substrates embedded with self-assembled SiO2 nanoparticle monolayers for SERS. She is currently pursuing her M.Sc. at the Nanyang Technological University and studying PVD and Nitriding techniques for steel hardening.
Colin Sheppard is Professor and Head of the Division of Bioengineering at National University of Singapore. Professor Sheppard received the MA and PhD degrees from Cambridge University, and a DSc from Oxford University. He was also Professor of Physics and Head of the Physical Optics Department at the University of Sydney for 14 years. He has served as Vice-President of the International Commission for Optics (ICO) and President of the International Society for Optics Within Life Sciences (OWLS), and is Editor-in-Chief of Journal of Optics A: Pure and Applied Optics. Professor Sheppard played a major role in the development of the confocal microscope, including launching the first commercial confocal microscope, and has received several awards, including a Humboldt Research Award for invention of the two-photon microscope.
Malini Olivo is currently Principal Investigator of the Photodynamic Treatment and Diagnosis and Biophotonics Laboratories in the Singapore National Cancer Centre and Singapore Health Research Facilities, Head of Biooptical Imaging at the Singapore Bioimaging Consortium and she also holds an Adjunct appointment in the Department of Pharmacy at the National University of Singapore. She has a PhD in Bio-Medical Physics. She has pioneered the area of clinical application of Photodynamic Diagnosis and Treatment in Cancer in Singapore and has initiated several collaborative projects in nanophotonics imaging applications in biomedical research. Her research interests include nanophotonics, optical bioimaging and photomedicine/photobiology.
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Kah, J.C.Y., Phonthammachai, N., Wan, R.C.Y. et al. Synthesis of gold nanoshells based on the depositionprecipitation process. Gold Bull 41, 23–36 (2008). https://doi.org/10.1007/BF03215620
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DOI: https://doi.org/10.1007/BF03215620