I. Novotny

Optimization of capacitive affinity sensors: drift suppression and signal amplification

The detection limit of capacitive affinity sensors based on the gold–alkanethiol system can be improved by optimization of sensor preparation and by signal amplification. The dissociation of the gold–sulfur binding is often a critical point leading to operative errors of such sensors. The stability of self-assembled monolayers prepared with different thiols on gold electrodes in aqueous and organic solvents was studied by the capacitive technique. The results show that monolayers made of 16-mercaptohexadecanoic acid are stable in aqueous solution and can be hardly extracted from a gold surface by ethanol, methanol, or dioxane, while a considerable damage of self-assembled monolayers was observed due to incubation in chloroform or dimethylformamide. In contrast, self-assembled monolayers made from short-chain disulfides or thiols (such as 3,3′-dithio-bis(propionic acid N-hydroxysuccinimide ester) or 11-mercaptoundecanoic acid) displayed a poor stability in aqueous phase. Capacitive affinity sensors based on these short-chain thiols showed a considerable drift of the signal. The use of long-chain thiols resulted in a stable signal; it was applied to compare capacitive effects due to immobilization of different biological molecules and for preparation of different biosensors. The response of capacitive biosensors can be amplified by formation of a sandwich structure. This principle was illustrated by subsequent adsorption of polyclonal anti-HSA after binding of HSA with a sensor for HSA based on monoclonal antibodies.

Self-assembled monolayers as selective filters for chemical sensors

The lateral electrical conductivity of gold layers with thickness in the nanometre range was found to decrease due to adsorption of mercury, water, iodine and sulphuric compounds onto the gold surface. A self-assembled monolayer of hexadecanethiol, deposited on the gold surface, blocked the effects of water and volatile sulphuric compounds on the lateral conductivity of the gold layers, but does not block the effects of iodine and mercury. The results indicate a selective permeability of hexadecanethiol monolayers for mercury vapour, thus providing a method for development of ultrathin filters for chemical sensors.

THIN FILMS IN BIOSENSORS

Abstract Thin films are used in every domain of biosensor systems as for sample handling, biological recognition and amplification, transduction and electronic signal processing. Several planar microelectrochemical chips with thin-film electrodes of different shapes and arrangements on Si or glass substrates have been developed and utilized in voltammetric and potentiometric sensors. Bilayer lipid membranes (BLMs) are very ‘‘adaptive’’ thin-film materials applicable in biosensors. Forming of BLMs on planar chip with thin-film electrodes has opened up new possibilities for the development of miniaturized biosensors as well as for basic research on electrical and mechanical properties of biological membranes.

Thin film non-symmetric microelectrode array for impedance monitoring of human skin

Abstract This paper introduces a new thin film non-symmetric array of microelectrodes for impedance diagnostics and characterization of hydroscopic properties of human skin. Using a suitable design of the planar thin film electrode system we change an orientation of vector intensity of the electric field lines from transversal to longitudinal direction relative to the skin surface. Electrical properties of measured system and electrostatic field of interdigitated array (IDA) electrodes were simulated. With regard to theoretical and simulated analyses, the non-symmetric interdigitated arrays of electrodes were designed and fabricated. Non-symmetric IDA electrodes were tested in KCl solutions and applied for impedance monitoring of human skin.

Sputtered yttrium oxide thin films appropriate for electrochemical sensors

Abstract This work deals with Y 2 O 3 thin films prepared by r.f. diode sputtering for application in electrochemical sensors. The influence of annealing on selected electrical and mechanical properties of Y 2 O 3 thin films has been studied. With increasing annealing temperature the values of electrical strength and electrical resistivity increase, whereas, the values of relative permittivity and Youngs modulus decrease. Yttrium oxide films have a polycrystalline structure without cubic structural change caused by annealing. The change from compressive to tensile stresses takes place in Y 2 O 3 films with increasing temperature. The properties of Y 2 O 3 thin films are comparable with the published data. The Y 2 O 3 film was used as an insulation layer in vertically arranged electrodes in a microelectrochemical cell. The redox recycling phenomenon was demonstrated with the redox couple [Fe(CN) 6 ] 3−/4− .

Preparation of transparent conductive AZO thin films for solar cells

A study of the effect of technology parameters (sputtering power, substrate temperature and post-deposition annealing) on structural, electrical and optical properties of aluminium-doped zinc oxide (AZO) thin films was carried out. The optimal technology parameters of preparation were found to get necessary properties of AZO thin films for application in solar cells - the high figure of merit (F ges 4 %/Omega), low electrical sheet resistance (Rs les 10 Omega/square) and high optical transmittance (T ges 82%, including the glass substrate).

Thin film voltammetric microsensor for heavy metal analysis

Thin film palladium (Pd) and indium tin oxide (ITO) microelectrodes modify by mercury (Hg) were developed for heavy metal analysis by anodic stripping voltammetry. In case of Pb/sup 2+/ determination the sensitivity of ITO-Hg array of disc electrodes was higher (130 nA//spl mu/M) in comparison with Pd-Hg interdigitated array of electrodes (60 nA//spl mu/M).

Piezoelectric ZnO thin films prepared by cyclic sputtering and etching technology

A novel procedure of ion assisted deposition technology consisting of cyclic sputtering and ion etching is presented. Cross-resistivities of ZnO films deposited by that technique increased up to 10/sup 10/ /spl Omega/cm due to the formation of buffer regions in the films. These ZnO films with the piezoelectric coefficient of the order of 10/sup -12/ m/V are applicable in low-frequency microactuators.

Preparation of shell nanocrystalline Ga-doped ZnO ultra-thin films by sputtering

In this paper the possibility to form ultra-thin homogenous films doped by Ga (ZnO:Ga) by continual or sequential sputtering is presented. An influence of post-deposition annealing on crystalline structure of films was studied. The ability to create a highly consistent coverage (shell) of three dimensional nanostructures (GaP nanowires) by the sequential mode of sputtering was proven.

Experimental Studies on Doped and Co-Doped ZnO Thin Films Prepared by RF Diode Sputtering

For decades zinc oxide (ZnO) has been in the spotlight due to its unique combination of semiconductor, piezoelectric, optical, and magnetic properties, which open perspectives for wide range of applications from optoelectronic and transparent electronic devices (Ohta & Hosono, 2004), surface and bulk acoustic wave devices and piezoelectric transducers (Wang et al., 2008), spintronics (Ji et al., 2008), to chemical and gas sensors (Carotta et al., 2009), and solar cells (Ganguly et al., 2004). Great industrial advantages of ZnO are its eco-friendly nature, wide abundant sources and low costs of metal Zn. ZnO is a group II-VI semiconductor with a direct band gap of 3.37 eV at room temperature, which can be modified (∼3 eV– 4 eV) via extrinsic doping with either cadmium (Cd) or magnesium (Mg). By its semiconductor properties ZnO is similar to gallium nitride (GaN) (Table 1).