Synthesis and characterization of dendrimer-stabilized nanoparticles

Abstract

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