Spectroscopy systems suitable for estimating the composition of test samples are disclosed. Embodiments of the present invention include an element that can be embedded within a sample and operatively couple with elements of the system located outside the sample, thereby enabling long-term monitoring of the sample. An embodiment includes radiation-emitting and radiation-detecting devices having periodic structures, such as photonic crystals and/or plasmonic metamaterials, which serve to filter the wavelengths of radiation at which they operate and/or enhance responsivity for those wavelengths. In some embodiments, the detecting devices are housed in a module suitable for long-term implantation within the sample. In some embodiments, the radiation-emitting and detecting devices are located external to the sample and are optically coupled with a mirror implanted within the sample. In some embodiments, an estimate of the composition of the test sample is generated at controller that is in communication with the emitter module.
