The first smart plasmonic absorber based on metal‐polymer bionanocomposites performing via conformational changes of the biological functional agent, i.e., a protein, is introduced. Such a progress is done through bridging the gaps between nanofluid filtration, plasmonics, and bioswitching. Initially, a biofunctionalized nanofibrous membrane is developed that could filter out metal nanoparticles (<100 nm) from an aqueous stream with a high separation efficiency (97%). This approach brings about a breakthrough in applicability of the macroporous nanofibrous membranes for rejection of suspended nanosolids and extends the application area beyond microfiltration (MF) to ultrafiltration (UF). This operative filtration in the next step leads to a novel synthesis route for plasmonic materials as formation of a smart free‐standing metal–polymer bionanocomposite able to act as an omnidirectional black absorber.