Optimized Silica Shell Synthesis Surrounding Gold Nanorods for Enhanced Spectroscopies
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Optimized Silica Shell Synthesis Surrounding Gold Nanorods for Enhanced Spectroscopies Marina Santana Vega1 · François Brisset2 · Guillaume Laurent1 Received: 20 August 2020 / Accepted: 9 November 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract We present a precise study for coating gold nanorods (GNRs) by a silica shell layer. Different parameters like pH, reaction time, and, most importantly, the ratio between the selected surfactant and the tetraethyl orthosilicate (TEOS) are studied and discussed. This latter is the key parameter to increase reproducibility, stability, reaction time, and the control of the targeted silica shell thickness. Moreover, the silica shell growth induces an optical shift of the localized surface plasmon resonance (LSPR) bands, which is explained by the change of the local refractive index. Both extinction spectroscopy and scanning electronic microscopy (SEM) are used to characterize the growth of the silica shell in time. Based on these results, it is thus possible to follow the growth process just by extinction spectroscopy, which ensures a rapid control of the reaction and makes it possible to stop it on time depending on the targeted shell thickness. Controlling the thickness is mandatory for further GNRs functionalization and surface plasmon enhanced spectroscopies. Keywords Gold nanorods · Silica shell synthesis · Core-shell materials · Spacer thickness control · Shell growth spectrometry monitoring
Introduction The design and development of new hybrid and functional systems are very important in field of materials science due to specific limitations such as the use and manipulation of colloidal particles (i.e., low stability, high chemical reactivity, and non-desired aggregation processes). To overcome some of these limitations, synthesis of core-shell structures using “bottom-up” approach shows many advantages. Silica for coating of colloidal particles, polymers, and surfactant aggregates have been widely used, especially for enhancement of colloidal stability [1]. More precisely, concerning colloidal systems, many different ones have been studied, such as metallic nanoparticles, semiconductors, magnetic, ceramic nanoparticles, and graphene coated with gold [2–6]. Using silica for coating material relies in its high stability, especially in aqueous media, but also on the easy regulation * Guillaume Laurent guillaume.laurent@ens‑cachan.fr 1
Université Paris-Saclay, ENS Paris-Saclay, CNRS, PPSM, 91190 Gif‑sur‑Yvette, France
UMR CNRS 8182, ICMMO, SP2M, Université Paris-Saclay, 91405 Orsay Cedex, France
2
of the coating process, chemical inertness, controlled porosity, adaptability, and optical transparency. Mainly two factors explain this stability [7]. The first one is that van der Waals interactions are much lower than those involving other nanoparticles. The second one is that cations and positively charged molecules can be tightly attached to the silica layer at silica-water interfaces under basic conditions. The consequence is t
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