Experimental evidences support the existence of an aggregation/disaggregation step in the Turkevich synthesis of gold nanoparticles.

Turkevich method is one of the most employed techniques to synthesize gold nanoparticles. Despite its simplicity, the mechanism has been an issue of debate over the past years. The general belief is that particles are formed by a classical nucleation and growth theory, originally described by LaMer's model. In the present work, we provide new experimental evidences that supports either LaMer's theory and their detractors. In the former model, it is proposed that particles are generated by a burst nucleation form the initial 'seeds', from which their growth in a second and quasi-independent step. Instead, our experiments (DLS, UV/VIS and TEM measurements) support the idea that nanoparticles 'seeds' tend to form large intermediate clusters at the beginning of the synthesis, that afterwards disassemble to yield the final nanoparticles. However, unlike other reports, we propose that during the cluster formation the particles do not coalesce, instead they come close to each other without losing their identity. As the synthesis continues, these clusters are progressively separated into the final particles. As a consequence, a path to synthesize ultra-narrow size nanoparticles is provided, along with their stability against salt aggregation, and shelf-time. We found that these ultra-homogeneous nanoparticles are stable for several months, making them suitable for many applications in the biomedical and analytical research.

In vitro bioaccessibility of lutein and zeaxanthin of yellow fleshed boiled potatoes.

Yellow fleshed potatoes contain significant amounts of lutein and zeaxanthin but the bioaccessibility of potato carotenoids has not yet been investigated. The purpose of this study was to estimate the in vitro bioaccessibility of carotenoids provided by potato. Lutein and zeaxanthin concentrations of boiled, freeze dried and milled samples of seven yellow fleshed potato accessions were determined by HPLC before and after different steps (gastric, duodenal and micellar phase) of in vitro digestion. The gastric and duodenal digestive stability of lutein and zeaxanthin in boiled tubers of the different accessions ranged from 70 to 95 % while the efficiency of micellarization ranged from 33 to 71 % for lutein and from 51 to 71 % for zeaxanthin. For all accessions, amounts of lutein and zeaxanthin after micellarization were significantly lower than the original amount found in the boiled samples. The accession 701862 showed the highest bioaccessible lutein concentration (280 µg/100 g, FW) and the accessions 703566 and 704218 showed the highest bioaccessible zeaxanthin concentration (above 600 µg/100 g, FW). Considering the mean potato intake in the Andes (500 g per day), the accession 701862 provides 14 % of the lutein intake suggested for health benefits and the accessions 703566 and 704218 provide 50 % more than the suggested zeaxanthin intake.