This work is part of a larger effort to miniaturize a microfluidic formaldehyde sensing device recently developed and commercialized by InAirSolutions Strasbourg 1. The detector is already an innovation in the field being capable to detect continuously formaldehyde concentrations lower than 1 ppb in stabilized conditions and long range campaigns, fulfilling the new imposed regulations in the field of indoor air pollution [1]. The sensing device works in four steps: i) gas sampling, ii) trapping of formaldehyde from air to a liquid reagent, iii) derivatization reaction with acetylacetone solution at 65°C producing a fluorescent compound (DDL), iv) colorimetric detection employing a commercial fluorescence detection system. Apart of increasing significantly the overall price of the system, the commercial fluorescence systems has a large dead volume decreasing the response time of the measurement process and increasing the necessary liquid flow rate. Starting from this current situation, one of the project goals is to develop a cheap miniaturized fluorescence sensing system. Finally, the aim is to develop an ultra-portable formaldehyde sensing device with larger autonomy and shorter response time compared to the current device, using the state of the art in the field of micro-fabrication, opto-fluidics and gas-liquid trapping/contacting. One of the major challenges in field of lab-on-a-chips is the integration of fluorescence optical sensors in ultra-portable, low maintenance, low power consumption, sensitive, reproducible and cheap platforms for small liquid samples sensing. Since the emergence of this field three decades ago, progress has been registered and different integration strategies of the fluorescence optical components have been tested by different research groups. Starting from the latest achievements to our knowledge in this field [2-5], a simple and relatively low-cost fluorescence sensing platform has been designed, 1 http://www.inairsolutions.fr/