In planta engineering of gold nanoparticles of desirable geometries by modulating growth conditions: an environment-friendly approach.

Unique properties of gold nanoparticles (AuNPs) can be achieved by manipulating their geometries. However, it is not known if the shapes and sizes of AuNPs can be modulated in planta. Here, we evaluated the accumulation of gold across taxonomically diverse plant species (alfalfa, cucumber, red clover, ryegrass, sunflower, and oregano). Significant variations were detected in the uptake of gold in the roots ranging from 500 ppm (ryegrass) to 2500 ppm (alfalfa). Alfalfa was selected for subsequent studies due to its ability to accumulate relatively large quantities of gold in its roots. Temporal analysis revealed that most of the AuNPs formed within 6 h of treatment, and the majority of them fall within the size range of 10-30 nm. Spherical AuNPs (1-50 nm) were detected ubiquitously across different treatments. To elucidate the effects of growth variables on the geometries of in planta synthesized AuNPs, alfalfa was subjected to KAuCl(4) (50 ppm) treatment for 3d under different pH, temperature, and light regimes. Interestingly, manipulation of growth conditions triggered a noticeable shift in the relative abundance of spherical, triangular, hexagonal, and rectangular AuNPs providing empirical evidence toward the feasibility of their in planta engineering.