Watercress-based gold nanoparticles: biosynthesis, mechanism of formation and study of their biocompatibility in vitro

To avoid the potential adverse effects of chemically-synthesised gold nanoparticles (AuNPs), a new method is developed for their biosynthesis using watercress total extract (WTE) and it is compared it with the citrate-based method. Synthesised AuNPs were characterised using transmission electron microscopy (TEM), particle size analysis and infrared spectroscopy (FTIR), and the mechanism and biocompatibility of WTE-based AuNPs were evaluated by MTT assay. The colour of the WTE-based AuNPs was directly changed from yellow to deep red without any intermediate colour change and spectrophotometric analysis showed significant differences in absorbance as well as peak surface plasmon resonance of synthesised AuNPs as compared with the use of sodium citrate. Formation of AuNPs in the WTE-based method was faster than the method using citrate. TEM pictures showed similar sizes of the AuNPs obtained by both methods, but WTE-based AuNPs were more spherical and the range of sizes provided minor differences with TEM results. FTIR confirmed the involvement of WTE compounds in the structure of AuNPs during biosynthesis and the MTT assay did not show any considerable anti-growth effect of WTE-based AuNPs on target cells. Hence, it seems clear that WTE-AuNPs could be used for various biological-related purposes including drug delivery, diagnosis and treatment of various diseases.