Surface Energy‐Controlled SERS Substrates for Molecular Concentration at Plasmonic Nanogaps

Abstract

Positioning probe molecules at electromagnetic hot spots with nanometer precision is required to achieve highly sensitive and reproducible surfaceenhanced Raman spectroscopy (SERS) analysis. In this article, molecular positioning at plasmonic nanogaps is reported using a high aspect ratio (HAR) plasmonic nanopillar array with a controlled surface energy. A largearea HAR plasmonic nanopillar array is generated using a nanolithographyfree simple process involving Ar plasma treatment applied to a smooth polymer surface and the subsequent evaporation of metal onto the polymer nanopillars. The surface energy can be precisely controlled through the selective removal of an adsorbed self-assembled monolayer of low surfaceenergy molecules prepared on the plasmonic nanopillars. This process can be used to tune the surface energy and provide a superhydrophobic surface with a water contact angle of 165.8° on the one hand or a hydrophilic surface with a water contact angle of 40.0° on the other. The highly tunable surface wettability is employed to systematically investigate the effects of the surface energy on the capillary-force-induced clustering among the HAR plasmonic nanopillars as well as on molecular concentration at the collapsed nanogaps present at the tops of the clustered nanopillars.

Quantitative and Specific Detection of Exosomal miRNAs for Accurate Diagnosis of Breast Cancer Using a Surface‐Enhanced Raman Scattering Sensor Based on Plasmonic Head‐Flocked Gold Nanopillars

“…To apply SERS for analysis of exosomal miRNA expression in diagnostics of breast cancer, we fabricated a plasmonic gold nanopillar SERS substrate (3 × 3 mm) by maskless reactive ion etching (RIE) of silicon wafers, followed by electron beam evaporation for gold deposition ( Figure A) . Plasmonic gold nanopillars control the size of the gap between plasmonic nanostructures with sub‐nanometer accuracy while providing a 3D environment beneficial for high molecular accessibility .…”

“…Nanopillars constituting the SERS substrate have a typical diameter of 200 nm, height of 800 nm, and the gap width between pillars ranging from 100 to 200 nm. Following the exposure of SERS substrates to analyte solutions and air drying, the plasmonic gold nanopillars lean towards each other because of capillary force developed between the nanopillars during solvent evaporation (Figure C) . This phenomena relied primarily on solvent wetting (also known as “Wenzel state”), which occurs due to attractive capillary forces among plasmonic gold nanopillars and their elastic deformation.…”

Engineering State‐of‐the‐Art Plasmonic Nanomaterials for SERS‐Based Clinical Liquid Biopsy Applications

“…Recently, the construction of nanostructure arrays with uniform nanogaps (10-20 nm) has been engineered by many alternative time-and cost-effective technologies, including template-assisted assembly, [54] laser interference lithography, [63] and laser-assisted nanoreplication methods. [64] These structures were created through the facile solvent wetting (Wenzel state) method, which provides attractive capillary forces among nanopillars (Figure 7a,b). One type of newly designed nanostructures is leaning nanopillar arrays that cluster together to form narrow interparticle gaps (1-10 nm) on the top of nanopillars.…”

Hedgehog Inspired CuO Nanowires/Cu2O Composites for Broadband Visible‐Light‐Driven Recyclable Surface Enhanced Raman Scattering

“…Such accurate label‐free and fingerprint detection technique has been considered as a promising and noninvasive POC diagnostic tool in various applications, such as environmental monitoring, drug detection, explosives analyses, as well as healthcare inspection . Due to small scattering cross sections of the detected molecules, a plenty of plasmonic nanostructures primarily based on the electromagnetic field enhancement are widely investigated, which usually rely on chemical syntheses or complex lithographic approaches to achieve high‐density of hotspots . Among them, laser processing is an intriguing approach to fabricate micro/nanostructures over a large area at a high speed .…”