A novel one-step synthesis of gold nanoparticles in an alginate gel matrix by solution plasma sputtering† Anyarat Watthanaphanit, * ab Gasidit Panomsuwan c and Nagahiro Saito ab We report a novel strategy to produce stable colloidal gold nanoparticles (AuNPs) in alginate aqueous solution which can be done in one step and without any chemicals. The AuNPs were produced by applying a voltage across a pair of gold electrodes which were immersed in alginate aqueous solution. Since the generation of AuNPs was caused by the sputtering of gold electrodes, the process was named the solution plasma sputtering (SPS) process. We utilize the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in a liquid environment, (2) to endow biocompatibility to the AuNPs, and (3) to provide colloidal stability to the AuNPs-alginate aqueous suspensions. The alginate concentrations were varied as 0.2, 0.5, and 0.9 %w/v. The concentration- dependent effect on the particle size of AuNPs, the physical absorption property and the stability of the AuNPs-alginate suspensions were studied. Results indicate that preparation of chemical-free colloidal AuNPs-alginate aqueous suspension is successful by the SPS process. The obtained colloidal suspensions were stable and able to retain their strong plasmon absorption bands within a reasonable time period. As a consequence, this is a high-potential technique to produce AuNPs suspended in alginate aqueous solution appropriate for biomedical applications. 1. Introduction The advancement of knowledge in nanotechnology enables gold nanoparticles (AuNPs) to offer great potential for diagnosis and therapy of disease in a variety of medical elds. 1–4 Owing to their high surface-to-volume ratios which offer lower detection limits and higher selectivity than conventional strategies, 5 the AuNPs have been studied to detect specic targets such as nerve gases, 6 ions, 7 DNAs, 8 and proteins. 9 For their therapeutic potential, AuNPs are utilized as drug delivery vehicles. The exibility in their size and shape as well as their versatility for functionali- zation have facilitated approaches for encapsulation of numerous therapeutic agents such as small drug molecules, 10,11 insulins, 12 and nucleic acids or genes. 13,14 As drug molecule carriers, they have been widely studied for application in anti- cancer therapy due to the enlarge requirement for new treat- ments in this area. 15 To consider AuNPs for any in vivo biomedical applications, it is important to conrm their biocompatibility. The particles should be passivated with a layer acting as biocompatible interface before administration into living organisms. Apart from chemical functionalization on the AuNP surface, 16–18 one common strategy to wrap the AuNPs with biocompatible layer is to disperse them in a natural substance such as herbs, 19 sugars, 20 and biopolymers, including: por- phyran, 21 chitosan, 12,22 and sodium alginate. 23,24 However, the pathway to produce AuNPs before dispersion is based on chemical reaction in which gold precursor (e.g., HAuCl 4 ) and/or reducing agent (e.g., NaBH 4 ,C 6 H 8 O 7 , and H 2 O 2 ) are required. This may be associated with biological toxicity. There is also some level of environmental impact occurring in the manufacturing process. Although the physical methods such as gamma irradiation 25,26 and UV photo-activation 27 are utilized to eliminate the use of reducing agents, the HAuCl 4 precursor is still required. In the present contribution, we propose a one-step prepa- ration of colloidal AuNPs in sodium alginate matrix (which thereaer called alginate). The AuNPs were produced from sputtering of gold electrodes, which were immersed in alginate aqueous solution, by the application of a potential difference. The process was named solution plasma sputtering (SPS) process. 28 We select alginate polymer as a matrix since it is one of the most commonly used materials for the encapsulation of biologicals. Its naturally block fashion is assumed to have an effect on the appearance of the encapsulated AuNPs. Apart from its potential safety issue, the alginate polymer can promote the a Green Mobility Collaborative Research Center, Nagoya University, Nagoya 464-8603, Japan. E-mail: anyarat@rd.numse.nagoya-u.ac.jp; Fax: +81-52-789-2796; Tel: +81-52- 789-2796 b Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan c Department of Materials Science and Engineering, Faculty of Engineering, Shibaura Institute of Technology, Tokyo 135-8548, Japan † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra45029e Cite this: RSC Adv. , 2014, 4, 1622 Received 11th September 2013 Accepted 18th November 2013 DOI: 10.1039/c3ra45029e www.rsc.org/advances 1622 | RSC Adv. , 2014, 4, 1622–1629 This journal is © The Royal Society of Chemistry 2014 RSC Advances PAPER Published on 20 November 2013. Downloaded by Shibaura Institute of Technology on 26/07/2014 07:32:17. View Article Online View Journal | View Issue