Engineered vertically-aligned carbon nanotube microarray for self-concentrated SERS detection

Abstract

Surface-enhanced Raman spectroscopy (SERS) is a high-sensitivity, label-free detection method that shows promise for various analytical applications. Hydrophobic low-adhesion surfaces make excellent SERS substrates since they allow the usage of trace analytes at low concentrations by efficiently enriching them into the SERS-active region. Herein, we introduce a hydrophobic surface-enhanced Raman scattering substrate based on engineered carbon nanotube arrays (CNT-SERS) and study the role of structural design in both micro- and nanoscales. This substrate has predetermined microstructures with a high aspect ratio, providing controlled self-enrichment capability. Likewise, the vertically aligned 3D surface porosity enables enhanced sensitivity, exhibiting an amplification in the SERS signal of ∼507.6%. The applicability of CNT-SERS to environmental science is shown by analyzing 5 nM of industrial dye (crystal violet) with 121 consecutive SERS measurements that exhibit distinct peaks from the molecules. We explore the underlying mechanics governing the enrichment behavior during analyte deposition on microarrays and discuss the effective strategies for designing hydrophobic SERS substrates. A theoretical model predicting the extent of concentration is developed and compared with the experimental results. In addition, we suggest a robust analyte concentration strategy inspired by plants in the Bromeliaceae family. The proposed method utilizes a hydrophobic yet flexible CNT SERS substrate that prevents roll-off failures during droplet loading.