Improved Synthesis of Gold and Silver Nanoshells

Abstract

Metallic nanoshells have been in evidence as multifunctional particles for optical and biomedical applications. Their surface plasmon resonance can be tuned over the electromagnetic spectrum by simply adjusting the shell thickness. Obtaining these particles, however, is a complex and time-consuming process, which involves the preparation and functionalization of silica nanoparticles, synthesis of very small metallic nanoparticles seeds, attachment of these seeds to the silica core, and, finally, growing of the shells in a solution commonly referred as K-gold. Here we present synthetic modifications that allow metallic nanoshells to be obtained in a faster and highly reproducible manner. The main improved steps include a procedure for quick preparation of 2.3 ± 0.5 nm gold particles and a faster approach to synthesize the silica cores. An investigation on the effect of the stirring speed on the shell growth showed that the optimal stirring speeds for gold and silver shells were 190 and 1500 rpm, respectively. In order to demonstrate the performance of the nanoshells fabricated by our method in a typical plasmonic application, a method to immobilize these particles on a glass slide was implemented. The immobilized nanoshells were used as substrates for the surface-enhanced Raman scattering from Nile Blue A.

Growth of silver-coated gold nanoshells with enhanced linear and nonlinear optical responses

“…The Au/SiO 2 nanoshells were prepared according to the method described by Alexandre and co-workers (Brito-Silva et al 2013) with some modifications. Specifically, silica nanospheres were prepared by mixing NH 3 ÁH 2 O (28 %), anhydrous ethanol, and TEOS in a 50 mL plastic tube.…”

“…The silica-metal nanoshells exhibit tunable surface plasmon resonances ranging from visible to infrared region by varying the composition, core size, and shell thickness. (Oldenburg et al 1998;Pham et al 2002;Lu et al 2003;Phonthammachai et al 2008;Liang et al 2011;Gomez et al 2012;Brito-Silva et al 2013;Nghiem et al 2013) Furthermore, the metal nanoshells have been widely used for plasmon-exciton coupling (Fofang et al 2008(Fofang et al , 2011, catalysis (Deng et al 2007), chemical sensing (Raschke et al 2004), biosensor , drug delivery (Bikram et al 2007), photothermal therapy (Coughlin et al 2014), surfaceenhanced Raman scattering (SERS) (Jackson and Halas 2004;Zhang and Guo 2009), and all-optical magnetic recording (Mayergoyz et al 2009). …”

Coating nonfunctionalized silica spheres with a high density of discrete silver nanoparticles

“…In particular, much interest has been placed on the coating of dielectric particles with metal nanoparticles 5 (Jiang and Liu, 2003;Jackson and Halas, 2001;Brito-Silva et al, 2013;Peterson et al, 2007). The resulting properties of these composite materials depend largely on their structure (Preston and Signorell, 2009;Tzounis et al, 2014;Pan et al, 2014).…”

Towards attomolar detection using a surface-enhanced Raman spectroscopy platform fabricated by nanosphere lithography

“…Dye molecules such as the rhodamine or Nile blue series are also of interest, since electronic resonance can be combined with surface enhancement leading to an even higher signal. 31,32 The LOD parameter is often reported with respect to either the surface concentration of the SERS platform or the number of molecules in the solution. For rhodamine 6G (R6G), LODs of between 10 −10 and 10 −18 mol/L have been reported.…”