Plasmonic Metal-Insulator-Metal Capped Polymer Nanopillars for SERS Analysis of Protein-Protein Interactions

The advancement of SERS as an analytical tool requires substrates that provide both sensitive and reproducible measurements. In this work, a gold-titanium dioxide-gold metal-insulator-metal capped polymer nanopillar array SERS substrate is presented and optimized for SERS-based biosensing applications. The optical properties of the multilayered nanoantenna array are investigated using a combination of simulation and experimental studies. It is found that hot spot engineering, the plasmon resonance of the array, and cavity structure optimization all contribute to fundamental SERS sensor properties such as enhancement factor and enhancement factor uniformity, which are critically studied using this highly tunable device. A spatially averaged enhancement factor of (2.4 ± 0.8) × 10⁷ with sufficient error for quantitative studies is demonstrated at an excitation wavelength of 633 nm. The label-free detection of protein-protein interactions on the metal-insulator-metal nanopillar array surface is then demonstrated including for the cancer biomarker cancer antigen 125 at a concentration of 100 ng/mL.