Nanoscale silver cluster embedded in artificial heterogeneous matrix consisting of protein and sodium polyacrylate Atanu Mitra ⁎ , Asim Bhaumik ⁎ Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India Received 3 May 2005; accepted 14 May 2006 Available online 12 June 2006 Abstract Nanoscale silver cluster protected by sodium polyacrylate (PAA) was prepared through the reduction of aqueous silver nitrate solution containing PAA. PAA concentration was varied against a fixed concentration of silver nitrate to optimize the PAA to metal ratio, in which stable colloidal solution of silver nanoparticles of 7±3 nm size could be obtained. These PAA-protected silver nanoparticles in clusters of nanoscale dimension (nanoclusters) were dispersed into the artificial heterogeneous matrix fabricated from aqueous solution of polyacrylate and protein (bovine serum albumin, BSA) by adjusting the pH in the acidic region. PAA-protected Ag-nanoparticle and Ag/PAA–BSA composites were characterized by UV–VIS spectroscopy and TEM. © 2006 Elsevier B.V. All rights reserved. Keywords: Nanocomposite; Polyacrylate; Silver nanoparticle; Transmission electron microscopy 1. Introduction Synthesis and characterization of metal nanoparticles is a subject of growing interest because of their unique optical, electrical, catalytic properties and potential for exploitation in the field of medicine, optoelectronics and many other frontier areas of science and technology [1–5]. To prepare the stable colloidal solution of metal nanoparticles, one of the most common ap- proaches is to cap the metal by a suitable chemical agent like polymer, surfactant, etc. having appropriate functional groups, which can interact with the metal surface. In the polymer-assisted synthesis, various physico-chemical properties including the rela- tive concentration of the polymer and its molecular weight, pH of the solution, etc. have profound influence on the morphology of the particles. Study on the morphological changes of these nano- particles is interesting since optical, electrical, catalytic or mag- netic properties are strongly dependent on the morphology of the particles. However, there is a limitation of the use of such colloid solution of metal nanoparticles in device fabrication or other technological applications, which are largely based on solid matrices. Hence, extensive research efforts have recently been directed to obtain nanoparticle as a solid phase within organic or inorganic host materials [6–9]. A wide variety of artificial com- posite materials with many interesting properties can be prepared through the electrostatic interaction of oppositely charged poly- electrolytes including different biopolymers and synthetic poly- mers [10,11]. One of the widely expanding research areas in this field is to fabricate composite film of polyions on solid surface using layer-by-layer deposition technique [12,13]. Many re- searchers have reported inclusion of the nanoscale metal particles in such composite films [14–18]. In contrast attempt to synthesize such composite materials with dispersed metal nanoparticles in bulk is limited. These nanocomposite materials might be interest- ing for electronics, optics as well as life science. Here in phase 1 of our work we have prepared silver nano- particles in sodium polyacrylate (PAA) solution. PAA-protected silver nanoparticles at various molar ratios (Ag:PAA) of silver ion to PAA were prepared to explore the effect of the concentration of polyacrylate on particle size. In phase 2, we have prepared Ag- protein composite by active loading (entrapping of silver nano- particle is achieved during fabrication of polyacrylate–protein composite) of silver in PAA–bovine serum albumin composite. Materials Letters 61 (2007) 659 – 662 www.elsevier.com/locate/matlet ⁎ Corresponding authors. Tel.: +91 33 2473 4971; fax: +91 33 2473 2805. E-mail addresses: msam@mahendra.iacs.res.in (A. Mitra), msab@mahendra.iacs.res.in (A. Bhaumik). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.05.039