Chitosan-Stabilized Noble Metal Nanoparticles: Study of their Shape Evolution and Post-Functionalization Properties

Abstract

Noble metal anisotropic nanostructures have achieved a growing interest in both academic and industrial domains mostly because of their shape-dependent plasmonic properties in the near-infrared region. In this paper, gold and gold-silver anisotropic nanostructures were synthesized in very high shape-yields through a wet, seed-mediated approach based on the use of nearly spherical silver nanoparticles as seeds and chitosan as stabilizing agent. Two chitosans of different origin and molecular properties were selected for the synthetic pathway, leading to the formation of variously sized and shaped end products. In detail, quite homogeneous nanoplatelets of about 25-nm size and 7-nm thickness or nearly spherical, highly porous nanocages of about 50-nm size were obtained, depending on the type of polysaccharide employed. The shape transition towards anisotropic morphologies occurred through a slow, spontaneous process, in which the chitosan nature seemed to play a key role. As expected, both nanoplatelets and nanocages exhibit shape-dependent plasmonic features and surface properties tunable for a variety of application fields. To prove this point, the nanostructures were successfully post-functionalized with poly(10,12-pentacosadiynoic acid) (PCDA), a carboxylic-endowed diacetylene able to anchor on noble metal substrates, to obtain versatile, chromic platforms suitable for sensing and spectroscopic purposes.

Versatile template-directed synthesis of gold nanocages with a predefined number of windows

“…As it can be adapted to numerous systems (noble and non noble metals, metal oxide or chalcogenide), it may enable a variety of fundamental studies and technological important applications in various fields including biological medicine, sensing and detection, energy conversion and catalysis. [71][72][73] Experimental Synthetic procedures of Au nanocages…”

Relaxation Phenomena in Chitosan-Au Nanoparticle Thin Films

“…Thus, the amount of SC added for the synthesis reaction should not increase the pH of the solution to above 6. Additionally, the CH 2 and OH groups of CS may act as reducing groups in the formation of Au nanoparticles [ 22 , 26 , 27 , 28 , 29 , 30 ]. Thus, in this work, the maximum stoichiometric ratio used is 1 mol of HAuCl 4 for 2 mol of SC to achieve pH 4.5.…”

“…Polymers also offer control over the rate of the reduction process and thus enable the production of nanoparticles of different sizes [ 25 ]. The possibility of stabilizing Au nanoparticles using CS has been reported in the literature [ 22 , 26 , 27 , 28 , 29 , 30 ]. As CS in solution is protonated and positively charged, it can be adsorbed onto the surfaces of Au nanoparticles because of the interaction between the amino groups in CS and Au nanoparticles [ 2 , 25 ].…”

“…For later applications, the conductivity mechanism of CS/AuNP nanocomposites needs to be addressed. However, the literature has mostly focused on the fabrication, microstructural characterization, and sensibility of CS/AuNPs biosensors [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. The conductive and relaxation properties of CS/AuNP films have not been reported.…”

Hydrophilic Quaternary Trimethyl Chitosan Stabilized Silver Nanoparticles: Synthesis, Characterization and Antimicrobial Activity.

“…However, the role of a stabilizing agent is highly essential to prevent agglomeration [7]. In this regard, the role of chitosan (CTS), which is a cationic amino polysaccharide copolymer of glucosamine and N-acetyl glucosamine [8,9], as a strong stabilizing agent of metal nanoparticles has already been established [10]. Also, the non-toxicity, biodegradability, film forming ability of chitosan and the ease with which it can be functionalized with other materials coupled with its inherent and fascinating antimicrobial properties further makes it an excellent candidate [10 -12].…”