Fabrication of a Room Temperature Electrochemical Gas Sensor Using Paper Substrate

Abstract

Recent increases in threats to public health, safety, and security have generated a need for more reliable and rapid detection of volatile and toxic gases. To achieve a reliable and versatile gas sensing system capable of being fabricated at the micro-scale a sensor with high selectivity, rapid response time, and low power requirements that is capable of being fabricated easily with low cost at the micro-scale is needed. A promising new approach to detecting gases is by electrochemical sensing using room temperature ionic liquids (RTILs) as the sensing electrolyte. Electrochemical methods of detecting gases provide superior selectivity with low power consumption and have a wide range of gases that can be detected. RTILs are stable conductive ionic compounds which are liquid at room temperature but that also have extremely low vapor pressure, high thermal stability, and wide potential windows. These traits combined with the capability of room temperature operation gives RTIL sensors a distinct edge over traditional heated gas sensing technology. Combining this fundamental sensor structure with electrochemical measurement techniques such as electrochemical impedance spectroscopy (EIS) and amperometry allows for simple and reliable detection of a variety of gases. The hurdle of delayed response of RTIL sensors due to diffusion of the target gas is overcome by ink jet printing the circuitry, electrodes and the RTIL on high temperature resistant, flame resistant paper. The added benefits of using the fabrication method of ink jet printing are reduced cost and in situ fabrication. Printing on paper reduces cost and adds flexibility and durability to open up this versatile sensor to applications such as wearable sensors as an early warning system for areas where hazardous gases can cause serious injury or even death and further incorporation of sensors in transit security, for instance by embedding them in luggage tags. This research presents a room temperature ionic liquid (RTIL) gas sensors printed with on flexible and low cost heat resistant paper substrate. The electrodes are ink jet printed using both indium tin oxide and gold ink separately to achieve the optimum design for reliability, speed, precision, selectivity, size and cost. The fabrication process for a 1mm x 1mm RTIL gas sensor is presented with the measured responses to methane and ammonia. This flexible, inexpensive, and wearable sensor structure allows for widespread deployment of gas sensing technology in security sensitive or crowded public, government, and transit areas.