Preparation and characterization of gold nanoparticles prepared with aqueous extracts of Lamiaceae plants and the effect of follow-up treatment with atmospheric pressure glow microdischarge

AbstractThe unique properties of gold nanoparticles (AuNPs) make them attractive for use in a number of fields, ranging from cosmetology to medicine. If AuNPs are to be widely used in industrial and medical applications, it is necessary to develop environmentally friendly methods for their synthesis. This can be accomplished by replacing the traditional chemical compounds for the reduction of the Au(III) ions to Au0 during AuNPs synthesis with natural plant extracts or with atmospheric pressure plasmas. Here, the properties of three aqueous plant extracts (Mentha piperita, Melissa officinalis, and Salvia officinalis) in the synthesis of AuNPs were compared and optimized under standardized conditions. The effects of the type of plant extract, the reaction temperature, and the precursor concentration on the production and size of the obtained AuNPs were examined using UV–Vis absorption spectrophotometry, dynamic light scattering (DLS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was observed that the size of the produced AuNPs was dependent on the aqueous plant extract used, and that under the optimized conditions, the aqueous leaf extract of M. piperita resulted in the production of AuNPs with the smallest volume-weighted diameter. Additionally, the bioactive compounds present in each extract were studied. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) indicated that different chemical groups could be involved in the AuNPs synthesis, while a Folin–Ciocalteu (FC) assay revealed a clear role of phenolic compounds. Finally, it was shown that the treatment of the synthesized AuNPs, which were obtained after bioreduction using the plant extracts, with atmospheric pressure glow microdischarge (μAPGD) resulted in their agglomeration and enlargement