Today, the self-assembled monolayer (SAM) approach for surface functionalization is regarded as highly versatile and compelling, especially in the immobilization of biomolecules and fabrication of novel supramolecular architectures. Most of the scientific articles recently published on biosensors use the concept of SAM to generate different surface functional groups for the immobilization of biomolecules such as antibodies, proteins, and enzymes. Due to the simplicity of the formation process and lack of requirement for costly instruments, this approach is prominent among researchers working in the field of surface functionalization and biosensing devices. Herein, we have reviewed a wide range of literature reports on electronic devices such as chemical sensors, biosensors and organic film transistors that use SAM concept for their purposes. In this review article, effort has been made to provide information about the SAM functionalization procedure, i.e. the technique used, the molarity of the SAM solution, and other physical/chemical conditions involved. Moreover, the fundamental concept of the monolayer, the types of monolayers on air/water interfaces, the techniques used for SAM formation on solid substrates and the use of SAMs for patterning are discussed.

Day by day demand of portable, low cost and efficient chemical/gas sensing devices is increasing due to world-wide industrial growth for various purposes such as environmental monitoring and health care. To fulfil this demand, nanostructured metal oxides can be used as active materials for chemical/gas sensors due to their high crystallinity, remarkable physical/chemical properties, ease of synthesis and low cost. In particular, (1-D) one-dimensional metal oxides nanostructures, such as nanowires, exhibit fast response, selectivity and stability due to their high surface to volume ratio, well-defined crystal orientations, controlled unidirectional electrical properties and self-heating phenomenon. Moreover, with the availability of large-scale production methods for nanowires growth such as thermal oxidation and evaporation-condensation growth, the development of highly efficient, low cost, portable and stable chemical sensing devices is possible. In the last two decades, tremendous advances have been achieved in 1-D nanostructured gas sensors ever since the pioneer work by E. Comini on the development of SnO2 nanobelt for gas sensor applications in 2002 is one such example from which many researchers began to explore the field of 1D-nanostrcture based chemical/gas sensor. In the field of metal oxides nanowires chemical/gas sensing devices, Sensor Lab (University of Brescia) have made major contributions. Over the years, different metal oxides such as SnO2, ZnO, WO3, NiO, CuO and their heterostructures have been grown in nanowire morphology and successfully integrated into chemoresistive gas sensing devices. Hence in this feature review article, Sensor Lab research on synthesis of metal oxide nanowires, novel heterostructures and their characterization and gas sensing performances under the exposure to different gas analytes have been presented. Moreover, some new strategies such as branched-like nanowire heterostructure, core-shell nanowire structures adopted to enhance the performance of nanowire based chemical sensor are presented in detail.