A hand-held formaldehyde (HCHO) gas detector has been developed. This fluorescence-based system uses a standard microscope glass slide both as a transducer and a sensor. The selective detection of gaseous formaldehyde is performed using the well-known Hantzsch reaction with Fluoral-P, which is chosen as a reagent. The sensor consists of a nanoporous thin film doped with the reagent, which allows capturing the pollutants molecules. The nanoporous films of polymers are prepared using the Sol-Gel method and are coated on the microscope slide by spin-coating, enabling reproducible coatings of various shapes and thicknesses. Experiments were carried out in the laboratory to calibrate the instrument, with the objective to perform measurements in indoor and outdoor conditions. The real-time monitoring allows detecting pollution peaks of formaldehyde.