(393k) Synthesis of Highly Concentrated Gold Nanoparticles: A Perspective for Industrial Batch Production Processes Based On Green Chemistry

Controlled synthesis of nanostructured materials with functional properties has been the center of attention during the last decade because of their unique size and shape-dependent properties (e.g. optical, electrical, magnetic, chemical, etc.). Therefore, several applications on diverse disciplines such as medical diagnosis based on imaging and cancer treatment research have recently been directed towards the use of nanomedicine.

Results have been successful in spite the fact that industrial scalability of these processes nowadays is still in development, for instance the colloidal gold production with high reproducibility and remarkable control of shape and size at concentrations in the range of parts per million has been established; nonetheless, reproducible and facile synthesis processes in order to obtain more concentrated colloidal dispersions of gold are yet to be developed.

The present study evaluates three different techniques for production of highly concentrate colloidal gold nanoparticles (hundreds of parts per million). The first synthesis is a green chemistry approach based on the use of essential oils extracted from plants such as pelargonium graveolens geranium and explores their use as both capping and reductive agents. The second synthesis uses sodium citrate as the reductive agent, polyvinylpyrrolidone (PVP) is used as capping agent, in addition, the process is carried out at room temperature (293.15 K) and the effect of ultrasonic dispersion is also studied. These two syntheses are contrasted with the well-known Turkevich method. It´s known that this last traditional synthetic pathway may generate colloidal instabilities when certain concentrations are required (> 40 ppm) due mainly to the electrical properties of the solid-liquid interface and its relation with the zeta potential. Finally, for these three procedures hydrogen potential (pH) and Temperature were followed rigorously in order to develop kinetic models.  Stability was monitored over time using UV-VIS-NIR spectroscopy.

The nanoparticles obtained from these techniques have been proven to be stable over relatively long periods of time (months), making these products very useful for biomedical applications and low cost of the reductive and capping agents used.

Nanoparticles were characterized by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Dynamic Light Scattering, Zeta potential, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and UV-VIS-NIR spectroscopy. Biocompatibility of nanoparticles and their capping agents was tested in-vitro using an MTT protocol in Chinese hamster ovarian cells (CHO), (i.e. by a cytotoxicity standard assay).