Electrochemical characterization of organosilane-functionalized nanostructured ITO surfaces

Abstract

The electroactivity of nanostructured indium tin oxide (ITO) has been investigated for its further use in applications such as sensing biological compounds by the analysis of redox active molecules. ITO films were fabricated by using electron beam evaporation at different substrate temperatures and subsequently annealed for promoting their crystallization. The morphology of the deposited material was monitored by scanning electron microscopy, confirming the deposition of either thin films or nanowires, depending on the substrate temperature. Electrochemical surface characterization revealed a 45 % increase in the electroactive surface area of nanostructured ITO with respect to thin films, one third lower than the geometrical surface area variation determined by atomic force microscopy. ITO surfaces were functionalized with a model organic molecule known as 6-(ferrocenyl)hexanethiol. The chemical attachment was done by means of a glycidoxy compound containing a reactive epoxy group, the so-called 3-glycidoxypropyltrimethoxy-silane. ITO functionalization was useful for determining the benefits of nanostructuration on the surface coverage of active molecules. Compared to ITO thin films, an increase in the total peak height of 140 % was observed for as-deposited nanostructured electrodes, whereas the same measurement for annealed electrodes resulted in an increase of more than 400 %. These preliminary results demonstrate the ability of nanostructured ITO to increase the surface-to-volume ratio, conductivity and surface area functionalization, features that highly benefit the performance of biosensors.

Organosilane-functionalization of nanostructured indium tin oxide films

“…We found that nanostructured geometrical surface area increases 2.5 times with respect to projected area. There is direct correlation between the latter and the increase in electroactive surface area with respect to thin ITO films, which yields enhanced sensitivity in terms of electrochemical performance [30]. This AFM image shows that we are able to fabricate nanostructured ITO films by controlling the electron beam evaporation conditions, according to recent publications [33,34].…”

“…As-deposited nanostructured ITO substrates were observed by scanning electron microscopy (SEM) and characterized by atomic force microscopy (AFM) for the determination of geometrical surface area. The electroactive surface area was measured by cyclic voltammetry (CV) and results are shown elsewhere [30]. Surface functionalization was monitored by X-ray photoelectron spectroscopy (XPS) as a microscopic characterization.…”

Towards Nanostructured ITO-Based Electrochemical Sensors: Fabrication, Characterization and Functionalization

“…Then, a ferrocene-labeled organic molecule was coupled to the GPTMS-derivatized electrodes as a proof-of-concept. Ferrocene's redox activity on nITO was detected by CV (Figure 3b), showing an increase in the oxidation peak height of more than 400% compared to tfITO [7,8]. …”

“…Deposition rate was set at 1 Ǻ/s during a total time of 2000 s. After the evaporation process, the samples were annealed at 600 °C for 1 h in nitrogen atmosphere to promote the ITO crystallization for optimal electrical conductivity and optical transparency. SEM images of the electrodes revealed nanowires with a mean diameter of 30 nm [7,8].…”

A Novel Transparent pH Sensor Based on a Nanostructured ITO Electrode Coated with [3,3′-Co(1,2-C2B9H11)2]-Doped Poly(pyrrole)

“…The morphology of the wires (long stick and seed at the tip) and the film composition reveal that the nanostructuration was produced by the self-vapor-liquid-solid (self-VLS) mechanism. The electrochemical surface area provided by such nanostructured electrode was proved to be an order of magnitude higher (in a projected area around 1 cm 2 ) than its thin film counterpart [10]. This enhanced surface area has proved useful for amperometric and impedance sensors in terms of sensitivity and limit of detection.…”