Large-scale fabrication of bi-functional nanostructured polymer surfaces for selective biomolecular adhesion.

The development of technologies allowing the fabrication of nanoscale chemical contrasts is of great interest, as it may allow study of fundamental aspects of cell adhesion at the level of single protein/receptor molecules, and for engineering a new generation of biological and chemical sensors. Recent works on bi-functional nanostructured surfaces containing chemical functions towards proteins (adhesive and repellent) have shown an increasingly immunoreaction-recognition sensitivity between antigen and antibody couples, indicating their increased availability for specific bioreactions. Patterning techniques allowing low-cost fabrication of regular arrays with chemically distinct nanoscale features, from sub-100 nm to several hundreds of nanometers, have to be developed to study this phenomenon in more detail and to favor the creation of a new generation of protein platforms. Recently, several research groups have adopted different technological approaches to create nanopatterned surfaces for biological applications, and details can be found in the recent review on the topic by Blatter et al. Among the serial techniques mentioned in the review, direct writing methods such as dip-pen lithography and electron-beam lithography have been successfully used to fabricate protein nanoarrays with well-ordered features and controlled size, shape, and pitch, hence offering the potential to develop protein biochips and biosensors. However, all these techniques suffer from limitations that are principally related to the sophistication of the required equipment and the need for clean-room facilities. Also, they are not really suitable for fabrication of patterned platforms over large areas (>few cm) and are strongly dependent on the substrate material (gold, TiO2, SiO2). A recent alternative to produce sub-100-nm nanopatterns with self-assembled monolayers (SAMs), without using lithography, has been described by H. Gao et al. They succeeded in transferring nanoscale patterns from porous alumina templates to gold and silicon surfaces. The pores in the templates spatially confine the self assembly of molecules on the exposed surfaces allowing the fabrication of SAM patterns over several cm with features down to 30 nm. The combination of plasma polymerization processes and colloidal lithography appears to be a promising technique for producing nanostructured, functionalized, polymer surfaces. This unique combination offers an inexpensive way of fabrication that may be easily transferred to industrial applications, since it is a parallel technique. The interest in plasma polymerization relies on the formation, on different substrates, of a large variety of homogeneous polymer layers with unique physico-chemical properties, which can be accurately controlled by the plasma parameters. In parallel, deposition of self-assembled layers of monodisperse nanospheres has been widely used because this technique offers the possibility of easy production of two-dimensional (2D) nanomasks over a large area at low cost. In a previous study, by combining these two methods, we succeeded in fabricating nanocraters of adhesive acrylic acid moieties inside a protein-repellent matrix. However, even if this method has shown promising results in the production of a chemical contrast on the surface with a resolution down to 100 nm, the fabrication process suffers from some limitations. Indeed, the poly(styrene) (PS) beads used for fabrication of the nanomask and oxygen-plasma etching used in this method both limit the fabrication process because the etching step is not trivial to monitor and it confers to the surface a particular shape (the crater form). Moreover, sub-100-nm structures can be difficult to obtain because the small PS particles tend to melt and merge due to the local warming of the system during the etching step. Furthermore, the reduction of the size of the nanoparticles by etching is limited because of the glass transition of the polymer beads, which occurs below a given diameter threshold. The use of inorganic nanoparticles such as silica can overcome these limitations: monodisperse silica nanoparticles, modified by a hydrophobic silane coupling agent, can be easily self-assembled into a (2D) hexagonal array at the water–air interface. This system, combined with the plasma polymerization technique, is potentially interesting for fabrication of nanostructured surfaces for several reasons: i) large-scale closely packed colloidal particle arrays can be easily obtained; ii) the size of the silica particles can be accurately tuned from a few nanometers to a few micrometers, thus allowing the control of the structural surface parameters with standard chemical laboratory facilities; iii) by controlling the growth rate of the plasma polymer deposition, the polymerization of the layer can proceed through the interstices of the colloidal particle layer; iv) the chemistry of the plasma polymer can be easily tuned. In this study, we report on a simple and inexpensive method for the fabrication of bi-functional nanostructured polymer surfaces with contrasted adhesive property over large surface areas. The method combines colloidal lithography (CL), using hydrophobic silica nanoparticles, and plasmaenhanced chemical vapor deposition (PE-CVD). In particular, we focus on the fabrication of bio-adhesive poly(acrylic acid) [!] Dr. F. Rossi, Dr. S. Mornet, Dr. F. Bretagnol, Dr. I. Mannelli, Dr. A. Valsesia, Dr. L. Sirghi, Dr. P. Colpo Nanotechnology and Molecular Imaging Unit European Commission Joint Research Centre Institute for Health and Consumer Protection Via E. Fermi, TP203, 21020 Ispra, VA (Italy) E-mail: francois.rossi@jrc.it [!!] The authors are very grateful to Mr. Takao Sasaki of the Nanotechnology and Molecular Imaging unit of the Institute for Health and Consumer Protection, Ispra, for the SEM images. This work has been performed in the framework of JRC Action 15008: ‘‘Nanobiotechnology for Health’’. : Supporting Information is available on the WWW under http:// www.small-journal.com or from the author.