CONCEPTION AND DEVELOPMENT OF MICROFABRICATED ELEMENTS FOR MICROFLUIDIC ANALYTICAL DEVICES

International audienceIn the last few years, researches have placed indoor air quality as the 9 th cause of global burden of disease [1]. In indoor environments, a wide range of VOCs are especially abundant such as BTEX (Benzene, Toluene, Ethylbenzene and Xylenes), aldehydes (acetaldehyde, hexanal) and ketones (acetone, 2-butanone). These VOCs present harmful effects on human health [2] even at low concentrations. ICPEES and In'Air Solutions have recently developed a portable miniaturized GC for real time detection of BTEX ppb levels [3], [4]. A laboratory prototype of this device was tested and validated under controlled conditions in the laboratory [3] and during two field campaigns in schools. In the latter, BTEX concentrations were for the first time measured continuously in different occupational conditions showing that these concentrations were higher in periods of school hours. Other VOCs, more precisely hexanal and 2-butanone, were also detected indicating the necessity of analysis of a wider range of pollutants. For this purpose, our work is focused on the conception and development of a multipollutants analyzer. The operating principle of our current device is described elsewhere [3]. In order to achieve a limit of detection down to few hundreds of ppt, an additional stage of preconcentration, based on thermal desorption, will be added. Portability and low energy consumption are of a great importance for on-site real time monitoring of indoor air quality. Therefore, our aim is to miniaturize the elements which are the bulkiest and require the highest energy supply in analytical devices. More specifically, micro-fabrication techniques were deployed so that different parts of two components, a pre-concentrator and a micro-column, were developed on wafers of small dimensions, 15 x 25 mm and 50 x 50 mm respectively. The combination of these microfabricated elements with integrated heaters and temperature sensors enables the fabrication of sensible analytical devices with very limited power consumption. In this work, heating elements and sensors for both devices were fabricated by means of metal deposition of titanium and silver using e-beam and Joule effect evaporation, respectively. In the microcolumn, the heating system is composed of four resistances of 82 Ω which allow an increase of the temperature from 25 °C to 200 °C in 150 s whereas two other resistances of 430 Ω act as temperature sensors (see Figure 1). In the case of preconcentrator, a faster raise of temperature is critical to achieve a quantitatively desorption of the VOC, thus a final temperature of 250 °C has to be reached in 10s. In order to determine the most suitable configuration t