Highly Dense and Accessible Nanogaps in Au–Ag Alloy Patterned Nanostructures for Surface-Enhanced Raman Spectroscopy Analysis

2020-05-22T22:14:27Z (GMT) by Taeksu Lee Soongeun Kwon Jae-Jong Lee
Well-tailored metal nanostructure arrays possessing a large number of small nanogaps have been highlighted because of their ability to enhance optical and electrical properties. In addition, it has been demonstrated that nanostructures with two or more elements present significantly enhanced and synergistic properties compared to those with a single element. However, the precise and reliable synthesis of bimetallic nanostructures possessing multiple nanogaps with high uniformity remains a major challenge. In this study, we propose the fabrication of bimetallic nanostructure patterns with numerous uncovered and external nanogaps. Silver dot arrays (SDAs) without organic capping ligands were developed via nanoimprint lithography, and several deposited Au–Ag alloy nanogranules were directly deposited on SDAs through a fast galvanic replacement reaction, without adding any additional reducing agents or capping molecules, to produce highly accessible nanogaps. These nanogaps surrounded by two types of metal elements demonstrated an excellent surface-enhanced Raman scattering (SERS) enhancement factor of up to 1.09 × 109, and the highly homogeneous SDAs led to high signal uniformity (relative standard deviation < 6.5 ± 0.3%) as well as device-to-device reproducibility. Finally, it was demonstrated that the synthesized substrates can be used as ultrasensitive and reliable SERS-based pesticide (malachite green) detection probes, down to a 10 fM concentration.