Long-period fiber gratings (LPFGs) represent an attractive fiber grating-based technological platform because of their selective spectral features together with the intrinsic sensitivity to surrounding refractive index (SRI). Unfortunately, their main limitation relies on the necessity to opportunely coat the glass substrate when sensitivity enhancement and/or specific functionalization are required. Here, we investigate the possibility to realize a self-functionalized and high-sensitivity LPFG by evanescent-wave interaction of the propagating light with a periodically patterned overlay. In particular, a D-shaped optical fiber is considered because of its peculiar geometrical features. First chemical etching is used to allow the evanescent-wave interaction of the propagating light with the surroundings with the desired sensitivity. Successively a uniform atactic polystyrene overlay is deposited onto the flat surface of the structure by …