Seeded growth of ultrathin gold nanoshells using polymer additives and microwave radiation

Laurent Lermusiaux,Mona Tréguer-Delapierre,Valérie Buissette,Thierry Le Mercier,Etienne Duguet,Laure Bertry,Marie Plissonneau,Glenna L Drisko

doi:10.1038/s41598-021-97171-0

Abstract

Nanoshells made of a silica core and a gold shell possess an optical response that is sensitive to nanometer-scale variations in shell thickness. The exponential red shift of the plasmon resonance with decreasing shell thickness makes ultrathin nanoshells (less than 10 nm) particularly interesting for broad and tuneable ranges of optical properties. Nanoshells are generally synthesised by coating gold onto seed-covered silica particles, producing continuous shells with a lower limit of 15 nm, due to an inhomogeneous droplet formation on the silica surface during the seed regrowth. In this paper, we investigate the effects of three variations of the synthesis protocol to favour ultrathin nanoshells: seed density, polymer additives and microwave treatment. We first maximised gold seed density around the silica core, but surprisingly its effect is limited. However, we found that the addition of polyvinylpyrrolidone during the shell synthesis leads to higher homogeneity and a thinner shell and that a post-synthetic thermal treatment using microwaves can further smooth the particle surface. This study brings new insights into the synthesis of metallic nanoshells, pushing the limits of ultrathin shell synthesis.

Highlights

Nanoshells made of a silica core and a gold shell possess an optical response that is sensitive to nanometer-scale variations in shell thickness
In order to study the effect of seed density on the synthesis of ultrathin gold nanoshells, we synthesised nanoshells using silica particles covered with different seed densities
Because the nanoshell synthesis is highly sensitive to different experimental conditions, the different samples were prepared in parallel, to minimise the effect of environmental parameters

Summary

Introduction

Nanoshells made of a silica core and a gold shell possess an optical response that is sensitive to nanometer-scale variations in shell thickness. The synthesis of gold nanoshells was first described by Oldenburg et al in three steps: surface amination of silica cores, deposition of Duff ’s seeds (2–3 nm gold seed) and regrowth of the seeds using a gold plating solution and a reducing agent[7]. The latter is preferentially formaldehyde because it favours a homogeneous seed growth as compared to sodium borohydride or hydroxylamine hydrochloride[8], and because it is more practical than gaseous CO9,10. Because of the high sensitivity of nanoshell synthesis to numerous parameters, to study the effects of a given parameter, it is primordial to synthesise reference samples under the same reaction conditions

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Conclusion