An apparatus, system, and method are disclosed for a frequency selective imager. In particular, the frequency selective imager includes an array of pixels arranged in a focal plane array. Each pixel includes at least one nanoparticle-sized diameter thermoelectric junction that is formed between nanowires of different compositions. When a nanoparticle-sized diameter thermoelectric junction senses a photon, the nanoparticle-sized diameter thermoelectric junction emits an electrical pulse voltage that is proportional to an energy level of the sensed photon. In one or more embodiments, the frequency selective imager is a frequency selective optical imager that is used to sense photons having optical frequencies. In at least one embodiment, at least one of the nanowires in the frequency selective imager is manufactured from a compound material including Bismuth (Bi) and Tellurium (Te).