. IntroductionPlasmonic metal nanoparticles (PNPs), in particular silver and gold NPs, have proven to serve as a versatile platform for a range of diverse applications including catalysis, [ 1,2 ] solar cells, [ 3 ] sensors, [4][5][6] especially based on surface plasmon resonance (SPR) [7][8][9] and surface-enhanced Raman scattering (SERS). [10][11][12] PNPs are distinct in their properties both from bulk materials and smaller superatomic metal clusters [ 13,14 ] in displaying SPR. SPR energy (wavelength) of PNPs is a function of nanoscale confi nement, as a result SPR can be advantageously manoeuvred [ 15 ] through several NP parameters including composition, size, and morphology. [16][17][18][19] Silver features the highest energy of d-sp transitions among coinage metals that enables SPR of silver nanoparticles (AgNPs) to span through the entire visible range into near-infrared (NIR) (ca. 395 nm to 1300+ nm). [ 18 ] Owing to their advantageous properties, AgNPs were synthesized in different morphologies including prisms, [ 5,18 ] cubes, [ 20 ] octahedra, [ 21 ] bars, [ 22 ] rods, [ 23,24 ] wires, [ 25 ] nanofl owers, [ 26 ] and particles with concaved-surfaces. [ 27 ] Several approaches to synthetic size and shape control of AgNP morphologies include systematic investigations of reducing agents, [ 28 ] capping agents, [ 29 ] synthetic parameters, [ 30 ] and photochemical transformation pathways. [ 23,31,32 ] Metal decahedral nanoparticles (MDeNPs) feature the most compact pentagonal-twinned morphology with D 5h symmetry. Decahedra are pentagonal bipyramids (Johnson solid J 13 ). AgDeNPs are enclosed with ten {111} triangular facets of face-centered cubic (fcc) close packed lattice. A decahedral particle can be also represented as consisting of fi ve tetrahedra twinned together by faces leaving a twinned defect gap of 7.35°. [ 33,34 ] Gold decahedral nanoparticles (AuDeNPs) were fi rst described as multiple twinned morphologies in the pioneering work of Ino and Ogawa [ 35,36 ] at an earlier stage of gold fi lm formation on alkali halide crystals and by evaporation in ultrahigh vacuum. Several approaches have been subsequently developed to produce, transform, and characterize MDeNPs. [ 24,37,39,42 ] A synthetic protocol to prepare high-quality monodisperse shape-selected gold decahedral nanoparticles in DMF, [ 37 ] and subsequent detailed studies of their plasmonic properties have been reported by Liz-Marzan and co-workers. [ 38,39 ] Several synthetic protocols to synthesize silver decahedral nanoparticles (AgDeNPs) were reported (see Table 1 ). Lombardi andThe key fi ndings in the synthesis and transformation of silver nanoparticles with pentagonal symmetries arising from regular multiple twinning are reported, researched in the last 5 years. In a one-stage photochemical synthesis of silver decahedral (pentagonal bipyramid, J 13 solid) nanoparticles (AgDeNPs), oxidative etching by hydrogen peroxide is implemented to achieve complete conversion of the small silver platelet precursor NPs. The concentration of hydr...