Hydrogel-Assisted 3D Volumetric Hotspot for Sensitive Detection by Surface-Enhanced Raman Spectroscopy.

Soo Hyun Lee,Sung-Gyu Park,Seunghun Lee,Chaewon Mun,Jun-Yeong Yang,Sunho Kim,Shin-Hyun Kim

doi:10.3390/ijms23021004

Abstract

Effective hotspot engineering with facile and cost-effective fabrication procedures is critical for the practical application of surface-enhanced Raman spectroscopy (SERS). We propose a SERS substrate composed of a metal film over polyimide nanopillars (MFPNs) with three-dimensional (3D) volumetric hotspots for this purpose. The 3D MFPNs were fabricated through a two-step process of maskless plasma etching and hydrogel encapsulation. The probe molecules dispersed in solution were highly concentrated in the 3D hydrogel networks, which provided a further enhancement of the SERS signals. SERS performance parameters such as the SERS enhancement factor, limit-of-detection, and signal reproducibility were investigated with Cyanine5 (Cy5) acid Raman dye solutions and were compared with those of hydrogel-free MFPNs with two-dimensional hotspots. The hydrogel-coated MFPNs enabled the reliable detection of Cy5 acid, even when the Cy5 concentration was as low as 100 pM. We believe that the 3D volumetric hotspots created by introducing a hydrogel layer onto plasmonic nanostructures demonstrate excellent potential for the sensitive and reproducible detection of toxic and hazardous molecules.

Highlights

Surface-enhanced Raman spectroscopy (SERS) is a powerful and promising technique for identifying molecular fingerprints corresponding to molecules’ vibrational energy states, enabling rapid, contactless, sensitive, label-free, and reliable chemical and biomedical analyses [1–7]
The amplification of Raman signals originates predominantly from an interaction of incident light with excited electron clouds of noble-metal (e.g., Ag, Au, and Cu) nanostructures (NSs), which is known as the localized surface plasmon resonance (LSPR) effect
The hydrogel-encapsulated metal film over polyimide nanopillars (MFPNs) with the 3D volumetric hotspots were fabricated via two-step maskless plasma etching and hydrogel coating (Scheme 1)

Summary

Introduction

Surface-enhanced Raman spectroscopy (SERS) is a powerful and promising technique for identifying molecular fingerprints corresponding to molecules’ vibrational energy states, enabling rapid, contactless, sensitive, label-free, and reliable chemical and biomedical analyses [1–7]. The amplification of Raman signals originates predominantly from an interaction of incident light with excited electron clouds of noble-metal (e.g., Ag, Au, and Cu) nanostructures (NSs), which is known as the localized surface plasmon resonance (LSPR) effect. The SERS technique has not been widely adopted in practical fields because of complicated fabrication processes, high costs, and poor signal uniformity and reproducibility. For polymer substrates in particular, this technique is favorable for fabricating NSs with high-areal density such as nanotunnels [18], nanodimples [19,20], and nanopillars [17,21] without mask patterning. The formation of such NSs is fundamentally related to complex surface dynamics, including crystallinity-dependent etching, surface migration, agglomeration, and coalescence [22,23]

Methods

Results

Conclusion