Performance of Impedimetric Biosensors Based on Anodically Formed Ti/TiO₂ Electrodes

Abstract

The advantages and limitations of impedimetric sensors based on Ti/TiO 2 architectures are described. Titanium dioxide (titania) was potentiostatically formed onto titanium electrodes of 2 mm diameter, at 10 and 30 V in 1 M H 2 SO 4 . The thickness of the titania layers was ellipsometrically determined to be 30 and 86 nm respectively and they are highly insulating with charge-transfer resistances in the MW range, as they were measured with electrochemical impedance spectroscopy under specific experimental conditions. Low voltage anodization (< 10 V) results to amorphous TiO 2 , whereas at higher applied voltages (> 25 V), anatase is the predominant form. SEM images are indicative of quite smooth, compact coatings without any severe cracks. Titania films were further treated with sodium hydroxide to increase the population of hydroxyl groups onto the outer oxide layer. Various silanization procedures based on liquid and gas-phase anhydrous conditions were employed to produce amino-terminated surfaces. Using glutaraldehyde as a cross linker, avidin was immobilized by chemical bonding. All impedimetric measurements were performed using biotinylated dextran as the target analyte. The initial conductivity of titanium/titania electrodes, as it can be managed by means of the hydroxylation process (duration of chemical etching) as well as the silane layer are major factors affecting the performance of the resultant biosensors. Extended studies using electrochemical impedance spectroscopy provided important new insights into the mechanism of the signal transduction and the physical factors that control the nature of the measuring signal.

Formation and mechanistic study of self-ordered TiO2 nanotubes on Ti substrate

“…In the past few years, high surface area and nanoporous TiO 2 nanotubes have attracted much attention for their potential use in several practical applications requiring an interconnected and large internal surface area, such as photoelectrochemical solar cells [1][2][3], electrochromic windows [4,5], photocatalyts [6], sensors [7], and Li ion batteries [8]. More recently, titania nanotubes with different sizes and various geometrical shapes were prepared using various physical and chemical synthesis routes such as sol-gel [9], template synthesis [10,11], hydrothermal process [12][13][14], and anodization [15].…”

Impedimetric immunosensors—A review

“…A comparative study between different silanization procedures was made and best results were obtained with GPMES deposited from an ethanol solution containing 5% (v/v) distilled water. Mantzila and Prodromidis [16] reported on the impedimetric behaviour of anodically formed Ti/TiO 2 electrodes. The effect of the initial conductivity of electrodes, managed by controlling the hydroxylation process (duration of chemical etching), and the effect of "silane" layers deposited through liquid or gas-phase based protocols on the stability and the origin of the measuring signal were studied.…”

“…The impedimetric response of the latter, in the format of a Nyquist plot, includes a curvature in the low frequency range, which represents the resistance of the insulating and biomolecule layers to species moving through the collapsed sites and pinholes within the film structure, and reflects the protective properties of these layers [3,4]. In some cases, the whole sensor assembly behaves as an electric circuit with two timeconstants ( = RC) [15,16].…”

“…Several instruments based on small-signal ac admittance measurements such as LCR-meters [14,33], impedance analyzers [11], lock-in amplifiers [21,36,37,51,65] and frequency response analyzers (FRA) [15,16,60,23,34,35] have been used to monitor interactions between biomolecules. The last two approaches are the most widely used and bring both inherent advantages and disadvantages.…”

Electrode Materials (Bulk Materials and Modification)

“…The difficulty to form a silane monolayer, compared to the simplicity of thiol chemisorption on gold, has limited the number of electrochemical sensors based on silane self-assembled monolayers. [497][498][499][500] Silane monolayers have found more applications in the domains of molecular electronics 501 or of sensors whose transduction mechanism is based on physical principles (e.g., surface acoustic wave) rather than on electrochemical ones. 502,503 The electrode surface can be modified by silanes via the sol-gel chemistry route, which leads to the formation of multimolecular layers.…”