Superhydrophobic SERS substrates based on silicon hierarchical nanostructures

Abstract

Silicon nanostructures have been cultivated as promising surface enhanced Raman scattering (SERS) substrates in terms of their low-loss optical resonance modes, facile functionalization, and compatibility with today's state-of-the-art CMOS techniques. However, unlike their plasmonic counterparts, the electromagnetic field enhancements induced by silicon nanostructures are relatively small, which restrict their SERS sensing limit to around 10 -7 M. To tackle this problem, we propose here a strategy for improving the SERS performance of silicon nanostructures by constructing silicon hierarchical nanostructures with a superhydrophobic surface. The hierarchical nanostructures are binary structures consisted of silicon nanowires (NWs) grown on micropyramids (MPs). After being modified with perfluorooctyltriethoxysilane (PFOT), the nanostructure surface shows a stable superhydrophobicity with a high contact angle of ∼160°. The substrate can allow for concentrating diluted analyte solutions into a specific area during the evaporation of the liquid droplet, whereby the analytes are aggregated into a small volume and can be easily detected by the silicon nanostructure SERS substrate. The analyte molecules (methylene blue: MB) enriched from an aqueous solution lower than 10 -8 M can be readily detected. Such a detection limit is ∼100-fold lower than the conventional SERS substrates made of silicon nanostructures. Additionally, the detection limit can be further improved by functionalizing gold nanoparticles onto silicon hierarchical nanostructures, whereby the superhydrophobic characteristics and plasmonic field enhancements can be combined synergistically to give a detection limit down to ∼10 -11 M. A gold nanoparticle-functionalized superhydrophobic substrate was employed to detect the spiked melamine in liquid milk. The results showed that the detection limit can be as low as 10 -5 M, highlighting the potential of the proposed superhydrophobic SERS substrate in practical food safety inspection applications.

Surface-Enhanced Raman Scattering Trace-Detection Platform Based on Continuous-Rolling-Assisted Evaporation on Superhydrophobic Surfaces

“…The signal intensities of characteristic bands at 1179 cm −1 (orange) and 1363 cm −1 (green) were, respectively, linear with the logarithm of CV concentrations. Therefore, the quantitative detection limit of the CRESHbased SERS platform was at least 3 orders of magnitude better than that of SH surfaces with previous static evaporation, 31,41 while comparable to that of state-of-the-art slippery surfaces. 24 To evaluate the spot-to-spot uniformity of the aggregate nanostructure fabricated based on CRESH, multiple Raman measurements were performed on the same CV/AuNP aggregate.…”

Bio-Inspired Hierarchical Micro/Nanostructured Surfaces for Superhydrophobic and Anti-Ice Applications

“…Inspired by Nature, scientists have designed superhydrophobic surfaces for many crucial applications such as anti-icing ( Onda et al, 1996 ; Lin et al, 2011 ; Latthe et al, 2019 ), biosensing ( Xu et al, 2017 ; He et al, 2018 ; Song et al, 2018 ; Xu et al, 2018 ; Xu et al, 2019 ), energy storage ( Sun et al, 2019 ), and surface-enhanced Raman scattering (SERS) ( Chen et al, 2018 ). The hierarchically structured surface was found to be one of the key factors for the superhydrophobic property because it provides a composite surface consisting of both solid surfaces as well as air pockets, thereby increasing the contact angle and rendering more repellent surfaces for water ( Feng et al, 2002 ; Liu et al, 2020b ; Wu et al, 2021 ).…”

Producing Fluorine- and Lubricant-Free Flexible Pathogen- and Blood-Repellent Surfaces Using Polysiloxane-Based Hierarchical Structures

“…9,10 This increased roughness provides the basis for Cassie−Baxter or Wenzel wetting states. 11,12 Conventional techniques to accomplish roughness include etching, 13−15 electrochemical deposition, 16,17 templating, 18,19 spray coatings, 20,21 sputtering followed by thermal annealing, 22 spin coating, 23 and sol−gel processes. 24 To closely replicate the lotus effect, researchers commonly employ a series of manufacturing steps to introduce a hierarchy of structures ranging from the nanometer to hundreds of micrometer lengthscales.…”

“…To develop repellent materials, researchers aim to create superhydrophobic surfaces characterized by contact angles >150 degrees and sliding angles <10° . Strategies such as physical modifications to add roughness inspired by the multiscale texture found on lotus leaves and butterfly wings are commonly used to create repellent surfaces. , This increased roughness provides the basis for Cassie–Baxter or Wenzel wetting states. , Conventional techniques to accomplish roughness include etching, − electrochemical deposition, , templating, , spray coatings, , sputtering followed by thermal annealing, spin coating, and sol–gel processes . To closely replicate the lotus effect, researchers commonly employ a series of manufacturing steps to introduce a hierarchy of structures ranging from the nanometer to hundreds of micrometer lengthscales. − By implementing multiple-step approaches, both micro- and nanoscale features are established on surfaces, which can be employed for biorepellency. ,, While these techniques have demonstrated high performance in terms of superhydrophobicity and pathogen repellency, it is often difficult to produce these surfaces on a large scale due to the complexities of the multistep manufacturing methods and the prohibitive costs of the reagents and processes involved …”