Hierarchical Superhydrophobic Device to Concentrate and Precisely Localize Water-Soluble Analytes: A Route to Environmental Analysis

Abstract

An efficient superhydrophobic concentrator is developed using a hierarchical superhydrophobic surface on which the evaporation of a sessile droplet (6 μL) drives the nonvolatile elements it contains on a predefined micrometric analytical surface (pedestal of 80 μm diameter). This hierarchical silicon surface exhibits a surface texture made of etched nanopillars and consists of micropillars and guiding lines, arranged in radial symmetry around the central pedestal. The guiding lines ensure the overall convergence of the sessile droplet toward the central pedestal during evaporation. The nanopillar texturing induced a delay in the Cassie−Baxter to Wenzel regime transition, until the edge of the droplet reaches the periphery of the pedestal. Experiments performed with polymer microparticles suspended in ultrapure water or with DNA molecules solubilized in ultrapure water at sub-fM concentrations demonstrated that the totality of the nonvolatile elements in the liquid microvolume is delivered on or close to the pedestal area, in a very reproducible manner. The very high concentration capacity of the device enabled the discrimination of the degree of purity of ultrapure water samples from different origins. The concentrator also turned out to be functional for raw water samples, opening possible applications to environmental analysis.

Surface-Enhanced Raman Spectroscopy (SERS) for Identifying Traces of Adenine in Organic-Bearing Extraterrestrial Dust Analogs Captured in the Tanpopo Aerogel after Hypervelocity Impacts

“…As a matter of fact, the miniaturization and automation of Raman instruments and the optimization of the robustness of SERS analysis (SERS substrate, etc.) could enable the development of onboard devices for space missions [30,31].…”

Droplet evaporation on superhydrophobic surfaces

“…108 Micro/nanostructured hierarchical SH silicon surfaces containing guiding lines which were arranged in radial symmetry around a central base were used as an efficient concentrator. 109 On these, evaporation of a sessile droplet of 6 μL formed residues on a micrometric analytical surface of 80 μm in diameter which was utilized as a SERS platform. The evaporating droplets slid toward the central base with the help of the guiding lines on this specific pattern.…”

“…The analysis of environmental or biological samples can be carried out where the discrimination of the degree of purity of pure water samples from different origins is possible (Figure 5). 109 Magnetic resonance methods were also used to image sessile droplets with volumes less than 10 mL on SH surfaces made of grown silicon nanofilaments on a 7 mm circular glass slide placed horizontally on a 3D printed acrylate insert in a 10 mm NMR tube. NMR images of the droplets were obtained and non-localised NMR spectra was used to track the droplet composition during evaporation.…”

“…SEM micrographs of the pedestal after ultrapure water droplet evaporation on a hierarchical superhydrophobic device, (C) Residue obtained after the evaporation of Milli-Q UPW water, (D) Residue obtained after the evaporation of cleanroom UPW water. Reproduced with permission from Fabre et al,Langmuir 38, 14249 (2022) 109. Copyright 2022 American Chemical Society.…”