Abstract: A device or apparatus includes a light source for providing light, a sensing element, and a detector. The sensing element includes nanofiber, which includes at least one oxygen sensitive compound, and can be excited by the light from the light source to emit radiation. The detector detects the radiation emitted from the nanofiber, and then provides a measured concentration of oxygen in the sample. The device or apparatus may include an enclosure defining an opening for introducing a sample for testing. The sensing element is disposed inside the enclosure. The device or apparatus may optionally include a heating element including an optically transparent and electrically conductive material. The device or apparatus may also optionally include at least one optical filter, a porous mask, a pre-amplifier, and other components. The method of making the device or apparatus, and the method using the device or apparatus are also provided.