Marleen Mescher

Ionophore-containing siloprene membranes: direct comparison between conventional ion-selective electrodes and silicon nanowire-based field-effect transistors.

Siloprene-based, ion-selective membranes (ISMs) were drop-casted onto a field-effect transistor device that consisted of a single-chip array of top-down prepared silicon nanowires (SiNWs). Within one array, two sets of SiNWs were covered with ISMs, each containing two different ionophores, allowing the simultaneous sensing of K and Na ions using a flow cell. It is shown that both ions can be effectively detected in the same solution over a wide concentration range from 10(-4) to 10(-1) M without interference. The ISMs were also analyzed in a conventional ISE configuration, allowing a direct comparison. While the responses for K(+) were similar for both sensor configurations, remarkably, the Na(+) response of the ISM-covered SiNW device was found to be higher than the one of the ISE configuration. The addition of a Na(+) buffering hydrogel layer between the SiO2 of the SiNW and the ISM reduced the response, showing the importance of keeping the boundary potential at the SiO2/ISM interface constant. The responses of the siloprene-covered SiNW devices were found to be stable over a period of at least 6 weeks, showing their potential as a multichannel sensor device.

Organic Surface Modification of Silicon Nanowire-Based Sensor Devices

The year 2011 marks the 10th anniversary of silicon nanowire (SiNW)-based electronic devices. Since their introduction (Cui & Lieber, 2001) SiNW-based sensor devices have gained considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species (Figure 1). Although SiOx coatings can be used for the detection of protons (Cui, 2001), and gases (Wan, 2009), the specific detection of other analytes, including ions and biomolecules requires the presence of an affinity layer that interacts with the analyte of interest. Such a layer can be added on top of the nanowire by the modification of the nanowire surface. In this chapter we review the surface modification strategies that have been explored on SiNW-based devices over the past decade.

Influence of Conductivity and Dielectric Constant of Water–Dioxane Mixtures on the Electrical Response of SiNW-Based FETs

In this study, we report on the electrical response of top-down, p-type silicon nanowire field-effect transistors exposed to water and mixtures of water and dioxane. First, the capacitive coupling of the back gate and the liquid gate via an Ag/AgCl electrode were compared in water. It was found that for liquid gating smaller potentials are needed to obtain similar responses of the nanowire compared to back gating. In the case of back gating, the applied potential couples through the buried oxide layer, indicating that the associated capacitance dominates all other capacitances involved during this mode of operation. Next, the devices were exposed to mixtures of water and dioxane to study the effect of these mixtures on the device characteristics, including the threshold voltage (VT). The VT dependency on the mixture composition was found to be related to the decreased dissociation of the surface silanol groups and the conductivity of the mixture used. This latter was confirmed by experiments with constant conductivity and varying water–dioxane mixtures.

Pulsed measurement method for characterizing chemical solutions using nanowire field effect transistors

This paper presents a method for characterizing chemical solutions using nanowire field effect transistors. A pulsed gate potential method is used to prevent instabilities related to the dynamics of ions and other charged species present in the solution. Applying this method realizes a significant increase of the stability of the drain current versus gate potential characteristics of the devices, enabling reproducible characterization of chemical solutions with nanowire field effect transistors in aqueous environments.