Sustainable synthesis and theoretical studies of polyhedral gold nanoparticles displaying high SERS activity, NIR absorption, and cellular uptake

The preparation of gold nanoparticles with multimodal properties such as near-infrared absorption, high surface-enhanced Raman scattering, cell internalization and low cytotoxicity is a challenging task. In this study, we developed a sustainable protocol to develop gold nanoparticles, using trisodium citrate as reducing, stabilizing, and shape-modulating agent at ambient conditions (25 °C). Reduction of gold salt at room temperature at a peculiar ratio R(Ccitrate/CHAuCl4) and concentration of reactants resulted in the formation of non-spherical, homogenous mixture of gold nanoparticles with polyhedral shapes. The protocol is extremely simple and does not even require stirring or mechanical shaking. The as-synthesized gold nanoparticles, even though multi-shaped, displayed a single monomodal peak in dynamic light scattering with polydispersity index of 0.098, representative of a fairly good monodisperse system. We investigated the optical properties of the nanoparticles both experimentally and by two-dimensional Finite-Difference-Time-Domain modeling. Due to the presence of shapes such as nanorods, nanotriangles, and prismatic, these nanoparticles exhibited a high surface-enhanced Raman scattering activity and a wide absorption range extending up to the near-infrared region, which makes them useful candidate for photothermal therapy too. We characterized the nanoparticles by electron microscopy, UV–vis–NIR spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. We have also developed an enhanced numerical diffusion limited aggregation model to simulate the growth of the particles, including the particle interfacial energy as a parameter of the system. Numerical results matched with the experimental data, and the model revealed being effective in reproducing size, shape, and morphological characteristics of non-spherical nanoparticles obtained under real experimental conditions. Finally, in vitro studies and nanoparticles cellular uptake were performed on a model cell line of mouse brain endothelium (bEnd.3) to assess biocompatibility. The main advantage of the proposed method lies in its simplicity with no other requirement like refluxing at elevated temperature, mechanical stirring, electromagnetic radiations, ultrasound, toxic chemicals, or seed mediation.