Factors Affecting the Preparation and Properties of Electrodeposited Silica Thin Films Functionalized with Amine or Thiol Groups

Abstract

Well-adherent sol-gel-derived silica films functionalized with amine or thiol groups have been electrogenerated on gold electrodes and both the deposition process and the film properties have been studied by various physicochemical techniques. Electrodeposition was achieved by combining the formation of a self-assembled "nanoglue" on the electrode surface, the sol-gel process, and the electrochemical manipulation of pH to catalyze polycondensation of the precursors. Gold electrodes pretreated with mercaptopropyltrimethoxysilane (MPTMS) were immersed in sol solutions containing the selected precursors (tetraethoxysilane, TEOS, in mixture with (3-aminopropyl)triethoxysilane, APTES, or MPTMS) where they underwent a cathodic electrolysis to generate the hydroxyl ions that are necessary to catalyze the formation of the organosilica films on the electrode surface. Special attention was given to analyze the effects of deposition time and applied potential and to compare APTES and MPTMS films. Characterization was made using quartz crystal microbalance, scanning electron microscopy, cyclic voltammetry, and atomic force microscopy (including in situ monitoring). The electrodeposition process was found to occur at two growing rates: a first slow stage giving rise to rather homogeneous, yet rough, films with thickness in the sub-mum range (increasing continuously when increasing the deposition time), which was followed by a faster gelification step resulting in much thicker (>1 microm) and rougher macroporous deposits. These two successive situations were observed independently on the applied potential except that more cathodic values led to narrower sub-microm ranges (as expected from the larger amounts of the electrogenerated hydroxyl catalyst). Thiol-functionalized silica films were deposited more rapidly than the amine ones and, for both of them, permeability to redox probe was found to decrease when increasing the film thickness because of higher resistance to mass transport.

Electroanalytical properties of haemoglobin in silica-nanocomposite films electrogenerated on pyrolitic graphite electrode

“…Electrogeneration parameters such as deposition time and applied potential influence the film thickness, its permeability to external reagents and its mechanical stability and thereby the voltammetric response of the modified electrode [17,18]. The effect of these two parameters was studied here for Hb-containing sol solutions by varying the applied potential between À1.0 and À1.4 V and deposition times ranging from 5 s to 60 s. The highest electrocatalytic currents, I cat , for oxygen response at PGE SiO 2 -Hb were observed when applying a deposition potential of À1.2 V and deposition time of 7 s. These optimum values are very close to those reported for similar films deposited on glassy carbon (E depos = À1.2 V and t depos = 10 s [23]).…”

“…Electrodeposition method shows a few advantages comparing to classic spin-coating and dip-coating methods, particularly the ability to control the thickness of the films, greater porosity and simplicity of procedure [15]. This was notably applied to get organically-functionalized silica thin films on electrodes [16][17][18] or well-structured and oriented deposits [19,20], which can be applied as sensitive nano-layers with good analytical performance [21,22]. Very recently, we have demonstrated that such an electro-assisted generation approach can be extremely useful for encapsulation of biomolecules, i.e., Hb and glucose oxidase, in silica thin films deposited on glassy carbon electrodes [23].…”

Organoclay-modified electrodes: preparation, characterization and recent electroanalytical applications

“…The group of Walcarius has extensively developed the structuration of electrode surfaces with inorganic thin films by using the sol-gel process which is suitable to generate uniform deposits of metal or semimetal oxides (mainly silica) and organic-inorganic hybrid thin films of controlled thickness, composition and porosity [200][201][202][203][204]. Intrinsically simple, this method can be achieved by electrolytic deposition from sol solutions [205,206].…”

Cheap and disposable gold and silver electrodes: Trends in the application of compact discs and digital versatile discs for electroanalytical chemistry

“…Sibottier et al [34] have reported the development of an amine or thiol functionalised electro-generated sol-gel-derived silica film at a Au CD based electrode. The electrochemical deposition of this film as reported to be achieved by the formation of a so-called "nanoglue" on the electrode surface.…”