The fabrication methods and the basic properties of the metal-oxide nanostructures referred as nanowires are presented and reviewed in this paper, with particular emphasis to the electrical and optical properties and their useful implementation for chemical and biochemical sensing. The field of chemical sensors has benefited by the wealth of highly crystalline nanostructures produced by physical and chemical methods. Large variation in bulk electrical conductivity, structural stability upon high temperature operation, high degree of crystalline ordering, large impact of point defects and surface states have unveiled the potential for the sensing field and have opened up new perspectives of application and for the realization of novel device architectures. This paper will summarize various techniques for preparation and characterization; then, the growth mechanisms and working principles will be discussed. Finally, the challenges that this field is currently facing are presented to signify the perspectives of expansion.

Ordered nanoscale pore systems such as those represented by zeolites offer many opportunities for the design of complex functional systems via self-assembly.With their large internal surface areas and tunable, well-defined crystalline pore structures that allow molecular sieving and ion exchange, zeolites can be adapted for numerous applications. The nanoscale reactors present in zeolite pore systems have been explored as structural templates for the spatial organization of numerous guests. Examples from various fields are discussed, such as the stabilization of organic dyes for the construction of energy transfer and storage systems, the construction of host–guest hybrid catalyst systems, and the encapsulation of conducting or semiconducting nanoscale wires and clusters. More complex, hierarchical forms of nanostructured matter become accessible when zeolite crystals are used as building blocks for the selfassembly of thin films or three-dimensional objects. A combination of weaker and stronger interactions ranging from dispersive forces, hydrogen bonding, and electrostatic interactions to covalent bonding can be used to build functional hierarchical constructs. Several examples and novel applications of such systems will be discussed, including oriented channel systems, chemical sensors, and hierarchical pore systems for catalytic reactions.

In this article, we present the Pico electronic nose, an artificial olfactory system based on thin-film semiconductor sensors, and two applications: food-quality control (coffee analysis) and environmental monitoring (odors at a landfill site). For both applications, the electronic nose data correlated with that of panels of trained judges. For the coffee, a global index (called the hedonic index) characterizing the sensorial appeal could be predicted with the electronic nose, and for the landfill site, the intensity of odors could be quantified. In this article, we stress the importance of stable and sensitive sensors, such as metal oxide thin films produced by sputtering, and of multivariate data analysis for extracting knowledge (e.g., gaining selectivity) from the data.

An electronic nose that uses an array of 32 polymer–carbon black composite sensors has been developed, trained, and tested. By selecting a variety of chemical functionalities in the polymers used to make sensors, it is possible to construct an array capable of identifying and quantifying a broad range of target compounds, such as alcohols and aromatics, and distinguishing isomers and enantiomers (mirror-image isomers). A model of the interaction between target molecules and the polymer–carbon black composite sensors is under development to aid in selecting the array members and to enable identification of compounds with responses not stored in the analysis library.