Second, we embedded QDs in films of poly(dimethylsiloxane) (PDMS), a transparent and gas-permeable polymer, for detecting low level of hydrogen sulfide. After exposing the film to 10ppm of hydrogen sulfide, the film loses its fluorescence within 1 min. However, the fluorescence recovers completely after the film is left in the open air for 2 h. Compared with other types of hydrogen sulfide sensors, the film sensor with embedded QDs is more portable, easy-to-operate and has low-cost.