By now long-period fiber gratings (LPFGs) represent a well-assessed in-fiber technology. Their peculiar spectral properties and the intrinsic surrounding refractive index (SRI) sensitivity, together with the well known advantages of optical fibers, make these structures one of the most powerful tools, especially in the sensing field. Unfortunately, their main limitation relies on the need of opportunely coating the glass substrate when significant sensitivity enhancement and/or specific functionalization are required. In this work, the possibility to realize a self-functionalized and high sensitivity LPFG is demonstrated. The principle of operation is based on the exploitation of the evanescent wave interaction of the propagating light with a periodically patterned overlay. A D-shaped optical fiber is used as fiber substrate, that is made SRI sensitive by means of wet chemical etching based on hydrofluoric acid. Due to its peculiar …