Carbon monoxide (CO) is a colourless and highly toxic gas. The detection of CO is a key requirement for safety and control in combustion processes. A number of sensors are currently available but all have drawbacks with most if not all having questions raised about their effective detection of CO over other gases such as hydrogen and methane. The power consumption of some methods of gas sensing is high as the active material must be heated to 400.600°C in order to function. The aim of this project was to attempt to eliminate this high power requirement and to study the design, fabrication and testing of CO sensors which function at room temperature, based on a supported platinum electrode in combination with a solid polymer electrolyte. It is therefore conceivable that the power source of such a sensor could be a battery, which could power a microcontroller and the relatively simple diagnostic testing equipment in a final commercial product.

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Conducting polymers entered the research field in late 70´s and efforts aimed at achieving printed electronics started a decade later. This thesis treats printable organic electrochemical transistors (OECT). Some conjugated polymers can be switched between a high conducting and a low conducting state in an electrochemical cell. In this thesis, the work carried out using poly(3,4-ethylenedioxythiophene) (PEDOT) as the active material in an electrochemical transistor is reported. The electrochemical transistors, presented, can be designed into a bi-stable and dynamic mode of operation. These transistors operates at voltages below 2V and current on/off ratios are typically 5000, but 105 have been reached. The transistor device can be built up from all-organic materials using common printing techniques such as with screen-printing. The bi-stable transistor can be combined with an electrochromic (EC) display cell to form a smart pixel circuit. Combining several of these smart pixels yield an actively addressed cross-point matrix display. From this an all-organic active matrix display printable on paper has been achieved. The OECT, combined with a resistor network was successfully used in inverter and logic circuits. One important feature of these organic electrochemical devices is that both ions and electrons are used as the charge (signal) carriers. This is of particular interest and importance for chemical sensors. By combining a proton-conducting electrolyte (Nafion®) that changes its conductivity upon exposure to humidity, a simple OECT humidity sensor was achieved. This proves the use of this OECT as the ion-to-electron transducer.