Adsorption of Trans-Zeatin on Laser-Ablated Gold Nanoparticles for Transport into Plant Cells and Growth Stimulation

Gold nanoparticles can serve as nanovectors for trans-zeatin, a natural cytokinin used in plant culture to stimulate growth and bud formation. Here, we have used Raman scattering, X-ray photoelectron spectroscopy, UV-vis absorption, transmission electron microscopy, and density functional theory calculations to explain the role of citrate anions in both the formation and the reactivity of the gold colloidal nanoparticles obtained by laser ablation and to go deeper inside into the interaction between metal and zeatin. In particular, the SERS (surface-enhanced Raman scattering) spectroscopy has been employed to study the adsorption of zeatin on different gold colloidal substrates. It is established that the molecule links to gold as tautomer N7(H), predominant in the aqueous suspension, in close similarity with adenine adsorbed on gold. Moreover, the laser ablation of a gold target in citrate solution results in small, stable, and reactive Au nanoparticles, able to transport zeatin inside plant cells, where it can act as a growth hormone.