Gold mesoflowers with a high density of multilevel long sharp tips: Synthesis and characterization

A one-step, aqueous-based, and surfactant-free method to synthesize gold mesoflowers (AuMFs) with multilevel long sharp tips is reported. The method enables control of the size, morphology, and optical properties of the AuMFs by tuning the reaction parameters such as concentration of precursor, halide, and reducing agent. The nanoparticle growth process is studied in detail and our findings suggest that chloride ions play a decisive role in the formation of long sharp tips and tip branching. The synthesized particles exhibit a tunable localized surface plasmon resonance (LSPR) response in the NIR and MIR regions (∼1800-3000 nm). These experimental observations are in agreement with simulations based on the finite-difference time-domain (FDTD) method. Moreover, the simulations also point towards a highly morphology-dependent field enhancement that opens up future applications of the AuMFs in surface-enhanced vibrational spectroscopy and sensing/therapeutics.