Role of Linear Carbon Chains in the Aggregation of Copper, Silver, and Gold Nanoparticles Luisa D’Urso,* ,† Giuseppe Grasso, † Elena Messina, † Corrado Bongiorno, ‡ Viviana Scuderi, ‡ Silvia Scalese, ‡ Orazio Puglisi, † Giuseppe Spoto, †,§ and Giuseppe Compagnini † Dipartimento di Scienze Chimiche, UniVersita ` di Catania, Viale Andrea Doria 6, 95125 Catania, Italy, Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Zona industriale VIII Strada n.5, I-95121 Catania, Italy, and Istituto Biostrutture e Bioimmagini, CNR, Viale Andrea Doria 6, Catania, Italy ReceiVed: October 8, 2009; ReVised Manuscript ReceiVed: NoVember 10, 2009 Most of the applications involving metal nanoparticles require a high resistance to aggregation and oxidation phenomena to preserve and modulate the peculiar reactivity, electronic, optical, and magnetic properties of nanoparticles. Linear carbon chains (LCCs) containing sp hybridization either as alternating triple and single bonds (polyynes) or with consecutive double bonds (cumulenes) are good candidates to create a shell that prevents such unwanted degradation phenomena. In addition, the development of reliable experimental protocols for their synthesis over a range of sizes and high monodispersity is an important challenging issue in most of the biological applications. In this Article, we investigate the interaction between LCCs and different metal nanoparticles (Cu, Au, Ag) to provide an insight into the factors influencing chemical (reactivity) and physical (optical) properties of the metal/LCCs core/shell systems produced at different experimental conditions. For this purpose, a range of different complementary experimental techniques such as Raman and UV-vis spectroscopy, transmission electron microscopy, and mass spectrometry are applied, and details on the different LCCs produced as well as insights into the metal-carbon bonds formed are unveiled. 1. Introduction In the past few years, the interest toward metals doped or bonded with carbon nanostructures has grown enormously, thanks to their wide use in optics and microelectronics applica- tions. 1 Many recent publications deal with the possibility to incorporate heteroatoms into carbon allotropes to significantly improve most of their physical properties. 2,3 Several works have also shown the possibility to build new carbon-based architec- tures by a fine-tuning of their morphologies, compositions, and carbon hybridizations. 4 It is well established that the reactivity of such carbon materials is greatly influenced by the carbon atoms hybridization state and/or by the presence of foreign elements. Encapsulation of metal nanoparticles into shells of particular compositions allows the tuning of the cluster size, to combine, in a synergic way, many properties of different materials and to manipulate the nanoparticles surface functions. 5 Homogeneously dispersed metal nanoparticles 6 are considered of great interest for their reactivity, electronic, optical, 7 and magnetic properties. For this reason, they are often employed in catalysis, biological applications, and clinic diagnosis. 8 On the other hand, metal nanoparticles are often susceptible to oxidation and aggregation (thus reducing their free energy), leading to a loss of their peculiar properties. Therefore, several efforts are devoted to protect metal nanoparticles with inert shells, to preserve them from surface modifications and to keep their main characteristics unchanged. To prevent the particles aggregation, stabilizing agents that bind to the nanoparticle surface are essential. Such agents can be organic ligands that allow the formation of organic-inorganic nanostructures with tailored functionalities. 9 Thiols, for example, have been widely used for the preparation of monolayer protected clusters, due to their strong affinity to noble metal surface. 10-12 Linear carbon chains (LCCs) containing sp hybridization either as alternating triple and single bonds (polyynes) or with consecutive double bonds (cumulenes) are good candidates to create the shell that prevents nanoparticles aggregation. 13,14 Carbon-coated metals might represent a new class of materials that could be employed for nanotechnology applications, mainly due to their protective role in the coagulation suppression and to their capability to interact with biological systems. In this respect, the production methods and the synthesis environment play a crucial role for a biocompatible interaction. Particularly, the pulsed laser ablation (PLA) technique has gained great favor as it allows one to synthesize new materials under vacuum or within dense environments (high pressure gases or liquids), giving the possibility to choose the ablation environment and, consequently, to drive some of the chemical and physical properties of the produced nanomaterials. 15-19 One extremely interesting way to produce these protected metal nanoparticles is a two-step PLA conducted in water. We have already investigated Ag/LCCs core/shell systems, and our experimental results draw the conclusion that the interaction of LCCs with colloidal silver results in the formation of a shell of LCCs organized on the particle surface with weak bonds. 13 Ag/carbon nanoparticles exhibit also enhanced localized electromagnetic fields that enabled highly sensitive vibrational spectroscopy analysis based on surface-enhanced Raman scattering (SERS). In this frame, we have applied mass spectrometry (MS) to directly detect the carbon species formed in the aqueous medium after the PLA procedure, and it was possible to distinguish between the different metal-carbon bonds formed by different experimental procedures of synthesis. 13 * Corresponding author. Phone: +39 095 7385129. Fax: +39 095 580138. E-mail: ldurso@unict.it. † Universita ` di Catania. ‡ Istituto per la Microelettronica e Microsistemi. § Istituto Biostrutture e Bioimmagini. J. Phys. Chem. C 2010, 114, 907–915 907 10.1021/jp9096309  2010 American Chemical Society Published on Web 11/24/2009