Electrogeneration of ultra-thin silica films for the functionalization of macroporous electrodes Fengli Qu a , Rihab Nasraoui a , Mathieu Etienne a , Yémima Bon Saint Côme b,c , Alexander Kuhn b , Jennifer Lenz b,c , Janine Gajdzik c , Rolf Hempelmann c , Alain Walcarius a, ⁎ a LCPME, CNRS-Nancy-Université, 405 rue de Vandœuvre, 54600 Villers-lès-Nancy, France b University Bordeaux 1, CNRS, ISM, ENSCBP, 16 Avenue Pey Berland, 33607 Pessac, France c Physical Chemistry, Campus B2.2, Saarland University, D-66123 Saarbruecken, Germany abstract article info Article history: Received 15 November 2010 Received in revised form 24 November 2010 Accepted 25 November 2010 Available online 3 December 2010 Keywords: Macroporous electrodes Sol–gel films Silica Electrodeposition Haemoglobin Electro-assisted generation of ultra-thin silica films can be achieved by using very dilute tetraethoxysilane (TEOS) precursors in the starting sol. The electrochemical manipulation of pH enables to catalyze polycondensation only at the electrode/solution interface, which offers the advantage of uniform deposition of thin layers onto the whole internal surfaces of macroporous gold electrodes, without any pore clogging effect. This opens promising avenues for application in various fields, as shown here for active biomolecule encapsulation. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Chemical modification and structuration at the micro- or nanoscale are effective ways to improve the behaviour of electrochemical devices [1]. Sol–gel-derived silica and organic–inorganic hybrids are attractive materials to modify electrode surfaces with thin layers [2]. Getting such films usually involves sol deposition by dropping, spin-coating, or dip-coating, and subsequent gelification upon solvent evaporation [3]. This operates well to generate, e.g., organically-modified silica layers [4], bioceramic composite coatings [5], or mesostructured silica films [6]. Ultra-thin films (b 100 nm) can be also obtained using diluted sol solutions [7]. These methods are however restricted to flat surfaces. An elegant alternative to overcome this limitation is the electro- assisted deposition via electrogeneration of polycondensation cata- lysts [8,9]. Recently, template approaches have emerged to produce ordered micrometer- and nanometer-scale porous electrodes, with the objectives of increasing the electroactive surface areas in comparison to the geometric ones, enhancing both molecular accessibility and rapid mass transport, and/or providing confined platforms to host suitable reagents [1,10,11]. Of particular interest are macroporous metallic electrodes with controlled architecture, which can be obtained by electrodeposition through uniformly packed 3D struc- tures of regularly arranged colloidal crystals [12,13]. The pore size can be typically tuned in the range from 0.1 to 2 μm. As maintaining large active surface areas and high degree of interconnection is a prerequisite to ensure high sensitivity, the surface modification of such macroporous electrodes should be restricted to ultra-thin layers. In the present paper, we propose an electrochemical strategy to deposit ultra-thin silica films onto the internal surface of macroporous gold electrodes, without blocking their interconnected porous struc- ture, demonstrating potential applications in bioelectrochemistry. 2. Experimental Homemade flat gold-coated glass plates, gold-coated quartz crystal resonators (P–QA–A9M–Au, BioLogic), and macroporous gold electrodes obtained via a derivative of the Langmuir–Blodgett technique [13,14]) have been used. Prior to use, they were treated in 30%–H 2 O 2 /96%–H 2 SO 4 (1:5 vol/vol) solution for 20 min and washed with water. Sol–gel films were potentiostatically deposited (-1.3 V for selected times) from precursor sols consisting of 20 mL ethanol (95–96%, Merck), 20 mL of 0.1M NaNO 3 and 240 μL of 0.1M HCl (37%, Riedel de Haen), to which tetraethoxysilane (TEOS, 99%, Sigma-Aldrich) was added to reach final concentrations in the 7– 340 mM range. Human haemoglobin (Hb, Mw 64,000, from Sigma) was sometimes added to the starting sol (typically 20–40 μM). Immediately after film deposition, the electrode was removed from the solution, rinsed with water, and dried at room temperature. Electrochemistry Communications 13 (2011) 138–142 ⁎ Corresponding author. Tel.: +33 3 83 68 52 59; fax: +33 3 83 27 54 44. E-mail address: alain.walcarius@lcpme.cnrs-nancy.fr (A. Walcarius). 1388-2481/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2010.11.034 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom