One-dimensional semiconductor nanostructures are unique sensing materials for the fabrication of gas sensors. In this article, gas sensors based on semiconducting nanowire field-effect transistors (FETs) are comprehensively reviewed. Individual nanowires or nanowire network films are usually used as the active detecting channels. In these sensors, a third electrode, which serves as the gate, is used to tune the carrier concentration of the nanowires to realize better sensing performance, including sensitivity, selectivity and response time, etc. The FET parameters can be modulated by the presence of the target gases and their change relate closely to the type and concentration of the gas molecules. In addition, extra controls such as metal decoration, local heating and light irradiation can be combined with the gate electrode to tune the nanowire channel and realize more effective gas sensing. With the help of micro-fabrication techniques, these sensors can be integrated into smart systems. Finally, some challenges for the future investigation and application of nanowire field-effect gas sensors are discussed.

Copper (II) oxide (CuO) is a metal oxide suitable for developing solid state gas sensors. Nevertheless, a detailed insight into the chemical-to-electrical transduction mechanisms between gas molecules and this metal oxide is still limited. Here, individual CuO nanowires were evaluated as ammonia (NH3) and hydrogen sulphide (H2S) sensors, validating the p-type character of this semiconductor. The working principle behind their performance was qualitatively modeled and it was concluded that adsorbed oxygen at the surface plays a key role necessary to explain the experimental data. Compared to their counterparts of SnO2 nanowires, an appreciable sensitivity enhancement to NH3 for concentrations below 100 ppm was demonstrated

Among the printing technologies for printed electronics, jet printing-based methods provide promising solutions to the fabrication of oxide-based thin film transistors (TFTs) for flexible and non-flexible electronics. Their direct patterning capability, non-vacuum and solution-based material formation process have attracted a significant amount of interests from both the academic and industry sectors. This topical review summarizes recent progress on the development of jet printed metal oxide TFTs with special attention given to the surface related effects, ink preparation and post-printing treatments, which are the critical aspects of obtaining high performance printed TFTs. Firstly, a brief introduction is made on the state of art jet printing technologies: the piezoelectric/thermal inkjet printing, the newly emerged electro-hydrodynamic jet printing and aerosol jet printing. Then, surface related issues of wettability and coffee-ring effect are discussed. Finally, jet printing of oxide-based TFTs is reviewed according to the classification of printed material types: metal oxide semiconductors, gate dielectrics and conductive electrodes. The extensive review of low temperature annealing methods make this work particularly interesting to the printing of oxide-based TFTs on flexible substrates.