Exceptionally Adaptable and Versatile SERS Platforms Enabled by Three-Dimensionally Transfer-Printed Nanowire Pattern Arrays

ConspectusSurface-enhanced Raman Spectroscopy (SERS) is a highly sensitive optical analysis technique that significantly amplifies the inelastic Raman scattered signals generated by molecular bonds. Due to its fingerprint-like specificity, rapid detection capabilities, and nondestructive nature, SERS has attracted widespread attention in recent years. It has found broad applications across various fields, including medical diagnostics, agricultural monitoring, and environmental analysis, leading to extensive research and development efforts aimed at advancing SERS-based technologies. In SERS, the role of nanostructures is of paramount importance, as they serve as platforms for enhancing Raman signals. However, one of the major challenges in utilizing these nanomaterials lies in controlling their spatial arrangement at the nanoscale. The difficulty in precisely positioning nanomaterials as desired leads to increased spot-to-spot variation, which in turn reduces the overall reliability and reproducibility of SERS sensors. To address these limitations, researchers have explored various large-area nanopatterning techniques that enable the uniform arrangement of nanostructures at well-defined intervals. Such techniques provide a promising strategy for enhancing SERS performance by improving signal uniformity and sensor consistency. In this Account, we introduce solvent-assisted nanotransfer printing (S-nTP), a cutting-edge nanopatterning technology that enables the fabrication of large-area, high-uniformity nanowire arrays. The S-nTP technique leverages directed self-assembly block copolymer (DSA-BCP) functionalization to produce large-area poly(methyl methacrylate) (PMMA) replicas from KrF/ArF lithography-patterned master templates. These PMMA replicas serve as templates for vertical deposition, allowing for the rapid, cost-effective, and scalable fabrication of nanowire arrays composed of various materials. A particularly noteworthy application of this technology is the formation of 3D woodpile structures, which are created by stacking nanowire arrays into vertically layered architectures. Within these highly ordered nanowire arrays, densely packed hot spots are generated, significantly enhancing the sensitivity, specificity, and signal reproducibility of SERS substrates. Moreover, both experimental and computational studies have been conducted to optimize the electric field (E-field) enhancement as a function of the nanowire array’s layer number. These studies demonstrate that the optimized number of layers and the evolution and expansion of hot spots facilitate label-free Raman analysis not only for small molecular structures but also for large biomolecules, such as proteins. Furthermore, this Account provides an in-depth overview of various SERS applications that take advantage of the unique properties of 3D woodpile nanostructures. These applications include surface functionalization strategies, multimodal sensing platforms, and machine learning-based multiplexing sensors. By leveraging these innovative approaches, researchers can develop next-generation SERS platforms with improved performance, enhanced reliability, and increased versatility. Collectively, these findings highlight the significant potential of novel 3D nanostructures, such as the woodpile configuration, as promising candidates for next-generation, high-performance, and highly reliable SERS substrates with multifunctional capabilities.