Self-Assembled Ag Nanocomposites into Ultra-Sensitive and Reproducible Large-Area SERS-Active Opaque Substrates.

Abeer Fahes,Suzanna Akil,Safi Jradi,Aotmane En Naciri,Mohammad Navvabpour

doi:10.3390/nano11082055

Abstract

This work describes a novel, one-shot strategy to fabricate ultrasensitive SERS sensors based on silver/poly(methyl methacrylate) (PMMA) nanocomposites. Upon spin coating of a dispersion of PMMA and silver precursor on N-doped silicon substrate, closely separated silver nanoparticles were self-assembled into uniform nanospheres. As a result, a thin hydrophobic PMMA layer embedded with Ag nanoparticles (AgNPs) was obtained on the whole silicon substrate. Consequently, a large-scale, reproducible SERS platform was produced through a rapid, simple, low-cost, and high-throughput technology. In addition, reproducible SERS features and high SERS enhancement factors were determined (SEF ~1015). This finding matches the highest SEF reported in literature to date (1014) for silver aggregates. The potential and novelty of this synthesis is that no reducing agent or copolymer was used, nor was any preliminary functionalization of the surface carried out. In addition, the AgNPs were fabricated directly on the substrate’s surface; consequently, there was no need for polymer etching. Then, the synthetic method was successfully applied to prepare opaque SERS platforms. Opaque surfaces are needed in photonic devices because of the absence of secondary back reflection, which makes optical analysis and applications easier.

Highlights

Surface-enhanced Raman spectroscopy (SERS), which integrates high levels of sensitivity with spectroscopic precision, provides huge enhancements to Raman signals of trace detection levels of chemical and biological molecules adsorbed on metal surfaces [1,2,3].The measured Raman signal enhancement in SERS shows impressive enhancement factors, up to 14–15 orders of magnitude, enabling the ultrasensitive identification of even single molecules [4,5].The ultrasensitivity of metallic-nanoparticle-based SERS substrates is usually linked to the high number of hotspots formed within the small interspaced gaps between the constituent nanostructures [6]
The main principle of this technique relies on the self-assembly of thin-layer poly(methyl methacrylate, poly(methyl methacrylate) (PMMA)) (Sigma-Aldrich, Kappelweg 1, Schn., Germany) into nanoholes, which are used as synthesis reactors for metallic NPs (MNPs)
The promising functions of Ag nanoparticles (AgNPs) as nanosensors can be optimized through the adjustment of diverse factors, including the concentration of the metal precursor, or the spin-coating speed

Summary

Introduction

The measured Raman signal enhancement in SERS shows impressive enhancement factors, up to 14–15 orders of magnitude, enabling the ultrasensitive identification of even single molecules [4,5]. The ultrasensitivity of metallic-nanoparticle-based SERS substrates is usually linked to the high number of hotspots formed within the small interspaced gaps between the constituent nanostructures [6]. The enhancement of the SERS signal is highly dependent on the plasmonic resonance frequency of synthesized nanoparticles (NPs) [7]. As a prerequisite for a maximum intensity SERS signal, there must be a close match between the wavelength (λ) of the plasmon resonance peak of the NPs and the. From an application standpoint, it is crucial to manipulate the interparticle spacings between metallic nanostructures and extract their optical properties

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Conclusion