Thermal stability of mesoporous silica-coated gold nanorods with different aspect ratios

Abstract

The effect of different temperatures (up to 900 °C) on the morphology of mesoporous silicacoated gold nanorods was systematically investigated. Gold nanorods with different aspect ratios (AR ranging from 2.5 to 4.3) were coated with a 15 nm thick mesoporous silica shell.Silicon supported monolayers of the particles were annealed in the temperature range of 300-900 °C. The resulting changes in particle morphology were investigated using scanning electron microscopy and visible wavelength extinction spectroscopy. The silica coating generally improved the stability of the nanorods from ca. 250 °C by several hundreds degree Celsius. For nanorods with AR<3 the shape and the aspect ratio change is only moderate up to 700 °C. At 900 °C these nanorods became spherical. For nanorods with AR>3, lower stability was found as the aspect ratio decrease was more significant and they transformed into spherical particles already at 700 °C. It was confirmed by investigating empty silica shells that the observed conformal change of the shell material when annealing core/shell particles is dictated by the deformation of the core particle. This also implies that a significant mechanical stress is exerted on the shell upon core deformation. In accordance with this, for the highest aspect ratio (AR~4) nanorod the shell breaks up at 900 °C and the gold cores were partially released and coalesced into large spherical particles.

In solution SERS sensing using mesoporous silica-coated gold nanorods

“…Silica is well-known as a biocompatible material and can be easily functionalized via a variety of silanol chemistry. 17 Encapsulation of AuNPs with silica shells will imbue the AuNPs with biostability, thermal stability, 18,19 and protection of cores from the environment. 20 Mesoporous silica (MS), 21,22 while maintaining the aforementioned advantages of silica, also offers a route for analyte molecule transport from the solution to the plasmonic core.…”

Photostability of Contrast Agents for Photoacoustics: The Case of Gold Nanorods

“…In particular, the most common shell material is silica or organosilica, which enables fine control over parameters as thickness or the level of porosity [ 159 ]. An enhancement of the photostability and thermal stability of gold nanorods after silanization has been observed by different authors, both in a continuous regime of thermal treatment [ 160 , 161 , 162 ] and upon optical excitation with ns- [ 63 , 82 , 156 , 163 , 164 ] as well as fs- [ 165 ] long pulses. The use of silanized gold nanorods for applications in PAI has been a subject of extensive research.…”

“…In a more recent work [ 108 ], some of us provided a quantitative definition of the threshold fluence for the onset of photoinstability in gold nanorods modified with organosilica, which improves by something in the order of 10 % on average per nm of shell thickness, in the case of a mercaptosilane precursor. Above this threshold, failure of the shell originates from its plastic deformation and eventual rupture due to elastic stress [ 161 , 165 ]. In the case of mesoporous silica, some authors have even reported that the eventual breakdown of the plasmonic system may depend on a leakage of fluid gold through interconnected pores or small breakpoints [ 165 ].…”

Single Particle Deformation and Analysis of Silica-Coated Gold Nanorods before and after Femtosecond Laser Pulse Excitation

“…Recently, it was shown that the thermal stability for oven-heated rods can be drastically enhanced by a mesoporous silica coating. 49 Under illumination of ns-pulses, mesoporous silica-coated gold nanorods were shown to be more stable as well. 50 , 51 Also, for photoacoustic imaging silica-coated gold nanorods are promising candidates because coating the Au nanorods with silica improved the imaging properties.…”