Synthesis and characterization of dendrimer-stabilized nanoparticles
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It has been posited that different synthetic conditions, such as use of amine-terminated rather than hydroxyl-terminated PAMAM dendrimers, may result in the production of different species of nanoparticles, namely dendrimer stabilized nanoparticles (DSNs) rather than dendrimer encapsulated nanoparticles (DENs). Although DENs have been well studied, DSNs have received little attention because they are larger, less uniformly synthesized, and probably catalytically inactive. Nonetheless, we believe that an understanding of these nanoparticle systems requires knowledge of all possible species being formed. Moreover, we hope that better synthetic control of DSNs may allow for new applications. To this end, we have optimized literature procedures to form gold DSNs smaller than 2 nm. Two techniques, aqueous-organic extraction and transmission electron microscopy staining, were explored for their utility in differentiating the two species (DENs and DSNs). UV-Vis absorption spectroscopy indicates that extraction serves as a useful qualitative method for identifying the presence of a significant proportion of DSNs in a solution of nanoparticles. If reproducibility can be established, we believe this technique could be made quantitative. Perfection of a washing step to remove excess thiols would allow for corroboration of current evidence using transmission electron microscopy (TEM) images. Attempts to stain the dendrimer for TEM using uranyl acetate and phosphotungstic acid were unable to match the quality of currently published data, although some progress was made in removing prohibitive stain contamination. We outline several experimental changes that may result in this technique yet proving useful.