# Large-Area Nanogap Platforms for Surface-Enhanced Raman Spectroscopy Toward Sensing Applications: Comparison Between Ag and Au

## TL;DR

This paper compares silver and gold nanogap structures for SERS, showing that silver provides much higher sensitivity for sensing chemicals and biomolecules.

## Contribution

The study demonstrates that Ag-based nanogap structures significantly outperform Au-based ones in SERS enhancement.

## Key findings

- Ag-based nanogap structures show 58x and 15x higher enhancement factors for bottom and top hotspots compared to Au.
- Enhanced detection in Ag structures is confirmed by simulations showing stronger electric fields in the nanogap.
- The results offer insights for designing more sensitive chemical and biomedical sensors using plasmonic nanostructures.

## Abstract

Sub-wavelength metallic nanostructures allow the squeezing of light within nanoscale regions, called plasmonic hotspots. Squeezed near-field light has been demonstrated to detect, modulate, and generate light in more effective ways. The enhanced electric field in the plasmonic hotspots are also utilized for identifying molecular fingerprints in a more sensitive manner, i.e., surface-enhanced Raman spectroscopy (SERS). SERS is a versatile tool used to characterize chemicals and biomolecules with the advantages of label-free detection, specificity, and high sensitivity compared to fluorescence and colorimetric sensing methods. With its practical and diverse applications such as biomedical sensing, the evaluation of SERS on diverse nano-structure platforms and materials is highly in demand. Nanogap structures are promising SERS platforms which can be fabricated over a large area with uniform nanoscale gap size. Here, we demonstrate the fabrication of large-area metal–insulator–metal nanogap structures with different metals (i.e., Au and Ag) and analyze material dependence on SERS. While both nanometer-sized gap structures exhibit a large enhancement factor for Raman spectroscopy, Ag-based structures exhibit 58- and 15-times-larger enhancement factors for bottom and top plasmonic hotspots, respectively. The enhanced detection on a silver nanogap platform is attributed to enhanced electric field in the gap, as confirmed by simulation. Our findings provide not only a way to better understand SERS in different metallic nano platforms but also insights for designing highly sensitive nanoscale chemical and biomedical sensors.