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Optimized Synthetic Protocols for Preparation of Versatile Plasmonic Platform Based on Silver Nanoparticles with Pentagonal Symmetries



The key findings 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, J13 solid) nanoparticles (AgDeNPs), oxidative etching by hydrogen peroxide is implemented to achieve complete conversion of the small silver platelet precursor NPs. The concentration of hydrogen peroxide is found to be optimal at 0.2 m. Such high peroxide concentration can be rationalized by its slow reactivity in a red-ox equilibrium with borohydride and citrate. We have also adapted light-emitting diodes (LEDs) as a light source and documented optimal exposure time, LED power, and wavelength range for convenient laboratory synthesis of high-purity size-selected AgDeNPs. In the absence of platelet impurities, AgDeNPs produce by the new-generation procedure can be conveniently re-grown into larger sizes using silver ions as a precursor. Thermal regrowth of new-generation AgDeNPs into pentagonal silver nanorods (AgPRNPs, J15 solid) can be reliably accomplished with the precise variation in rod length (by varying amounts of added silver) and width (by using different seed AgDeNPs). With the reported reproducible synthetic protocols that can be readily implemented in any chemistry laboratory, AgDeNPs and AgPRNPs should serve as a versatile plasmonic platform with a precisely tunable surface plasmon resonance (SPR) from ca. 430 nm (rounded AgDeNPs) to 1100+ nm (longitudinal SPR of longer AgPRNPs). The plasmonic platform based on the reported AgNPs with pentagonal symmetries should be practical for a diverse range of applications, especially plasmonic sensing and surface-enhanced Raman spectroscopy.