Durable Plasmonic Cap Arrays on Flexible Substrate with Real-Time Optical Tunability for High-Fidelity SERS Devices

Active tunable plasmonic cap arrays were fabricated on a flexible stretchable substrate using a combination of colloidal lithography, lift-up soft lithography, and subsequent electrostatic assembly of gold nanoparticles. The arrangement of the plasmonic caps could be tuned under external strain to deform the substrate in reversible. Real-time variation in the arrangement could be used to tune the optical properties and the electromagnetic field enhancement, thereby a proving a promising mechanism for optimizing the SERS sensitivity

Shape Control of Ag Nanostructures for Practical SERS Substrates

Large-area, highly ordered, Ag-nanostructured arrays with various geometrical features were prepared for use as surface-enhanced Raman scattering (SERS)-active substrates by the self-assembly of inorganic particles on an SU-8 surface, followed by particle embedding and Ag vapor deposition. By adjusting the embedding time of the inorganic particles, the size of the Ag nanogap between the geometrically separated hole arrays and bowl-shaped arrays could be controlled in the range of 60 nm to 190 nm. More importantly, the SU-8 surface was covered with hexagonally ordered nanopillars, which were formed as a result of isotropic dry etching of the interstices, leading to triangular-shaped Ag plates on nanopillar arrays after Ag vapor deposition. The size and sharpness of the triangular Ag nanoplates and nanoscale roughness of the bottom surface were adjusted by controlling the etching time. The potential of the various Ag nanostructures for use as practical SERS substrates was verified by the detection of a low concentration of benzenethiol. Finite-difference time-domain (FDTD) methodology was used to demonstrate the SERS-activities of these highly controllable substrates by calculating the electric field intensity distribution on the metallic nanostructures. These substrates, with high sensitivity and simple shape-controllability, provide a practical SERS-based sensing platform

Freestanding and Arrayed Nanoporous Microcylinders for Highly Active 3D SERS Substrate

Surface-enhanced Raman scattering (SERS) has been considered as one of the most promising tools for molecular analysis. To develop practical platforms, a variety of nanoparticles and two-dimensional (2D) nanostructures have been prepared. However, low signal intensity or slow binding kinetics in conventional approaches limits their applications. To overcome these shortcomings, production and usage of three-dimensional (3D) nanostructures remain an important yet unmet need. In this paper, we report novel and effective SERS-active materials by fabricating hierarchically structured SiO₂ microcylinders decorated with gold nanoparticles. In order to fully develop 3D nanostructures, while maintaining fast diffusion of analyte molecules, we used self-assembled nanostructures of block-copolymers (BCPs) confined in the microholes of an imprinting mold; the BCPs could provide a template for producing 3D nanostructure composed of nanofibers with sub-100 nm diameter through their microphase separation, whereas the imprinting technique provided cylindrical geometry for the local confinement of the BCPs. Microcylinders with nanodomains were then transformed into microcylinders with 3D nanopores via reactive-ion etching and, subsequently, their nanopores were decorated by gold nanoparticles. The resultant 3D nanopores enable a high loading of gold nanoparticles and formation of abundant hot spots and microcylinders facilitate the fast diffusion of analyte molecules through the nanopores, resulting in significant enhancement of SERS intensity