An environmental sensor comprises a graphene thin-film as an environmentally responsive material. Such graphene films exhibit negative temperature coefficients (NTC), resulting in rapid decreases in electrical resistance as temperature increases, as well as a much faster response time than any other NTC material reported in the literature. The graphene film is also mechanically stable under bending, and, therefore, can be adapted for use in a mechanical sensor or pressure sensor, because the electrical resistance of the graphene film changes upon deflection and/or changes in pressure. The electrical resistance of the graphene film also increases in response to increases in environmental humidity. The electrical resistance changes of the graphene film can also be used as a sensing mechanism for changes in chemical and biological parameters in the environment of the sensor.