The 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

In this work we successfully utilized 1% (m/v) aqueous leaf extracts and 1% (v/v) natural essential oils originating from Eucalyptus globulus and Rosmarinus officinalis as bioreducing and capping agents for gold nanoparticles (AuNPs) synthesis. UV/Vis absorption spectra revealed that AuNPs were well-dispersed and spherical when synthesized with E. globulus aqueous leaf extract, but also with R. officinalis aqueous leaf extract and its essential oil. Only AuNPs fabricated by utilizing E. globulus essential oil exhibited various shapes and a partial aggregation. TEM analysis showed that the average sizes of AuNPs produced with the aid of E. globulus aqueous leaf extract and its essential oil were 12.8±6.3nm and 42.2±42.0nm, while in the case of R. officinalis, resultant AuNPs reached 8.66±2.03nm and 60.7±60.6nm in diameter, respectively. By EDS, Au, O, and C were detected in all tested nanofluids. Functional groups of organic compounds occurring in the investigated aqueous plant extracts and essential oils were identified by ATR-FTIR, and they were established as quite similar among the analyzed plant extracts, but also among the essential oils. Finally, GC-MS analysis were implemented to determine the key constituents of the E. globulus and R. officinalis aqueous extracts and their essential oils