Nanoporous- micropatterned- superhydrophobic surfaces as harvesting agents for few low molecular weight molecules F. Gentile a,b,⇑ , M.L. Coluccio a,b , A. Accardo a,b,c , M. Asande b , G. Cojoc b,d , F. Mecarini a , G. Das a , C. Liberale a , F. De Angelis a , P. Candeloro b , P. Decuzzi b,e , E. Di Fabrizio a,b a Italian Institute of Technology, Via Morego 30, 16163 Genova, Italy b BioNEM (Bio Nano Engineering and Technology for Medicine), University Magna Graecia of Catanzaro, Catanzaro 88100, Italy c Soft Matter Structures Group ID13, MICROFOCUS Beamline European Synchrotron Radiation Facility, Grenoble Cedex, France d Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany e The Methodist Hospital Research Institute, Dept. of Nanomedicine and Biomedical Engineering, 6670 Bertner Ave, Houston, Texas 77030, USA article info Article history: Available online 30 December 2010 Keywords: Nanoporous silicon Superhydrophobic surfaces Low molecular weight molecules harvesting Early detection Cancer abstract Superhydrophobic surfaces were fabricated comprising cylindrical micro-pillars arranged in a regular hexagonal lattice. These structures are hierarchical in that the pillars incorporate, on the top, nanoporous silicon films. In sight of the superhydrophobicity of the system, the devices retain the ability of manip- ulating and concentrating diluted biological solutions, while, on account of the nanoporous films, they would efficiently filter the biological content of such solutions. The major advance, here, is the simulta- neous use of the properties above, and thus important applications are envisioned where extremely small quantities of bio-markers are efficiently extracted from serum and analyzed employing conventional and well assessed spectroscopy techniques. Ultra low concentrated small Rhodamine molecules were here efficiently analyzed using FTIR spectroscopy techniques, thus demonstrating that these devices are effective. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Super-hydrophobicity is a phenomenon whereby a drop post upon a surface would preserve its original spherical shape rather than wetting indefinitely the plane of contact [1,2]. The theoretical conundrum explaining this mechanism dates back to the mid for- ties of the last century and is very well assessed [1–4]. In the cel- ebrated model of Cassie [4], a surface would be super- hydrophobic on account of the pockets of air that remain trapped between the liquid and the substrate, and the smaller the fraction of solid in contact with the drop (u) the larger the apparent contact angle. At the limit of u ? 0, the drop would paradoxically float in air. Superhydrophobic surfaces (SHSs) retain unique properties in terms of wettability that can be reviewed as follows: (i) SHSs have superior non adhesive properties, in the sense that they exhibit vanishing small friction coefficients; (ii) a droplet, post upon these surfaces, would accordingly preserve a quasi-spherical shape dur- ing evaporation, and the contact area at the interface would thus progressively reduce; (iii) SHSs can be artificially reproduced using micro- and nano- fabrication techniques. Conveniently combining the properties above with nano-geometry based spectroscopy, mi- cro textured surfaces can be designed towards the goal of concen- trating and analyzing, with unprecedented accuracy, extremely diluted solutions of biological interest, which would be otherwise undetectable through conventional methods, as reported in [5]. This technology may find valuable application in the field of early cancer diagnostic. In fact, while it is very well understood that blood contains a number of proteomic molecules or biomark- ers that may reveal the occurrence of a tumour, their identification is still an open issue in that the proteins at study are very often very low abundant or, at best, extremely diluted [6–9]. In these re- gards, a superhydrophobic based device would proficiently boost the clinical use of plasma. In this work, conventional silicon, microtextured surfaces were revised to include the benefits of nanoporous silicon (NPSi) films. Substrates were fabricated comprising micrometer pillars arranged to form a regular, hexagonal lattice (Fig. 1A). NPSi films were pre- pared upon the pillars through a process of Si anodic dissolution (Fig. 1B and C). While simple, untreated Si is intrinsically hydro- philic, and NPSi manifests an apparent contact angle as large as 130°, these micro/nano hierarchical structures reveal an increased contact angle approaching 170° (Fig. 1D), and this may be ex- plained by a dual scale roughness. 0167-9317/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2010.12.076 ⇑ Corresponding author at: Italian Institute of Technology, Via Morego, 30, 16163 Genova, Italy. E-mail address: gentile@unicz.it (F. Gentile). Microelectronic Engineering 88 (2011) 1749–1752 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee