Thermo-induced Electromagnetic Coupling in Gold/Polymer Hybrid Plasmonic Structures Probed by Surface-Enhanced Raman Scattering

Abstract

This paper describes a general stepwise strategy combining diazonium salt, surface-initiated atom transfer radical polymerization (SI-ATRP), and click chemistry for an efficient gold surface functionalization by poly(N-isopropylacrylamide) (PNIPAM) brushes and gold nanoparticle assemblies. We designed by this way a new plasmonic device made of gold nanoparticles separated from a gold film through a thermoresponsive polymer layer. This organic layer responds to temperature variations by conformational changes (with a characteristic temperature called the lower critical solution temperature, LCST) and is therefore able to vary the distance between the gold nanoparticles and the gold film. The optical properties of these stimulable substrates were probed by surface-enhanced raman scattering (SERS) using methylene blue (MB) as a molecular probe. We show that an increase of the external temperature reversibly induces a significant enhancement of the MB SERS signal. This was attributed to a stronger interaction between the gold nanoparticles and the gold substrate. The temperature-responsive plasmonic devices developed in this paper thus provide a dynamic SERS platform, with thermally switchable electromagnetic coupling between the gold nanoparticles and the gold surface.

Controlling dynamic SERS hot spots on a monolayer film of Fe3O4@Au nanoparticles by a magnetic field

“…This led to shrinkage of the interparticle spacing to a size suitable for generation of more effective SERS hot spots. Further evidence of the contribution of the shrinkage came from temperature-and pH-induced formation of reversible hot spots [28][29][30][31]. In the present study, a similar change in SERS effect was observed, i.e., the SERS signal was very weak at the beginning of introduction of an external magnetic field, reaching maximum intensity after 5 s, and became stable thereafter.…”

“…Wang et al developed approaches to accomplish the dynamic assembly of nanostructures for controlling optical, electronic, and magnetic properties [27]. In other studies, the interparticle spacing was dynamically controlled using nanoparticles decorated with temperature-responsive polymer as a substrate [28][29][30]. Lu et al fabricated a nanoparticle monolayer film through the LangmuirBlodgett approach and transferred it to a temperature-responsive polymer substrate.…”

“…Gehan et al used a polymer chain as a switch between Au nanoparticles and the Au surface. The scattering signal could be dynamically tuned using a temperature-responsive polymer layer [29]. Thus, they obtained a dynamic SERS platform with thermally switchable EM coupling between Au nanoparticles and the Au surface.…”

A new plasmonic device made of gold nanoparticles and temperature responsive polymer brush on a silicon substrate

“…Of particular interest is the probability to check the interaction between Au or Ag NPs on the polymer layer to optimize the Raman increment factor, for instance, via the use of polymer films of different thickneses [6][7][8]. Recently, pH and thermally switchable systems made of Agadsorbed hydrogels or layer-by-layer films and core-shell NPs coated with poly(Nisopropylacrylamide) were used for SERS applications having dynamically control the distance between Au or Ag NPs and the molecular probes on flat Au surface [9][10][11].…”

Amino covalent binding approach on iron oxide nanoparticle surface: Toward biological applications

“…If these radicals are present during the synthesis of Fe 3 O 4 NPs, these aryl radicals form NPs modified with aryl groups through covalent linkages affording to a highly stable anchoring of the organic coating at the surface of the NPs. Diazonium salts have been widely used as coupling agents for the grafting of polymer coatings upon carbon-based 28 and metallic 29 (platinum, ruthenium, palladium, gold and titanium) planar and/or NP surfaces, affording strong linkages.…”