Continuous mechanical tuning of plasmonic nanoassemblies for tunable and selective SERS platforms
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S Key Laboratory of Soft Matter Chemistry, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China. 2 Department of Biological and Environmental Engineering, Hefei University, Hefei 230601, China. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 14 May 2020 / Revised: 7 August 2020 / Accepted: 2 September 2020
ABSTRACT The continuous tuning of plasmonic nanoassembly’s structure is the key to manipulate their optical and catalytic properties. Herein, we report a strategy of using macroscopic deformation to continuously tune the structure and optical activity of massive plasmonic nanoassemblies that are embedded in elastic polymer matrix. Plasmonic gold nanoparticles (Au NPs) are assembled to nanochains (Au NCs) with defined length and further embedded into polyvinylpyrrolidone (PVP) matrix. The nanostructure and plasmonic properties of massive Au NCs in this Au NCs-PVP film can be simultaneously and continuously tuned, simply by reversible mechanical deformation of this elastic film. In this way, the surface-enhanced Raman scattering (SERS) enhancement factor of this film as a SERS substrate can be mechanically modulated in the range of 100 to 6.8 ×107. Meanwhile, the PVP matrix also serves as a selective diffusion barrier to eliminate the fluorescence interference of large biomolecules, which enables the Au NCs-PVP film as a convenient SERS substrate for quick and direct analysis of small molecule analytes in biological samples and food, avoiding the complicate and time-consuming sample pretreatment process.
KEYWORDS surface-enhanced Raman scattering (SERS), plasmonic hotspots, nanoassembly, gold nanoparticles, bioanalysis
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Introduction
Plasmonic metal nanomaterials, especially gold nanoparticles (Au NPs), have been intensively studied for a wide range of applications including photothermal conversion [1], chemical sensing [2], optoelectronics [3], and photocatalysis [4, 5]. While Au NPs offer many scientific challenges and applications, nanoassembly of Au NPs shows unique coupled plasmonic properties [6]. Particularly, plasmonic “hotspots” are sub-10-nm space between coinage metal nanomaterials (such as Au NPs), where the near-field coupling of localized surface plasmon greatly enhances the Raman signals of analytes in hotspots [7]. Therefore, surface-enhanced Raman scattering (SERS) has become an ultra-sensitive analytical technique with great temporal and spatial resolution [2], which has been widely applied to single molecule detection [8, 9], biosensing and biomedical analysis [10–12], environmental and food analysis [13]. Designing SERS platforms with uniform hotspots structure, high enhancement factor (EF) and good reproducibility are prerequisites to the practical applications of SERS techniques [14, 15]. To better control the hotspot’s structure between Au NPs, several strategies have been developed to assemble Au NPs into ordered nanoassembly, such as using molecular linker
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