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Forschungsarbeit

Size Selective “Fishing” of Metal Nanoparticles using the Polymer Cage

by Ziyin Fan (19.01.2016)

This research topic introduces a unique polymer cage that can encapsulate metal nanoparticles (NPs) in a narrow size range (< 15 nm) with high efficiency. Large NPs are excluded from the polymer cage. Based on this novel property, polymer cages can be applied to separate metal nanoparticles based on their sizes. This process is called as “size selective fishing”. 

Size and shape are the most essential factors determining the properties of the metal NPs, such as surface plasmon resonance, catalytic activity and magnetic property. Versatile separation techniques have been developed for the size sorting of NPs, for example the membrane filtration and size exclusive chromatography. In contrast to the current techniques, a straight forward “fishing” process describes the size separation of metal nanoparticles using the polymer cage with a predetermined size. Using gold nanoparticles (AuNPs) as demonstration, a novel “graft-around” method that was recently developed in our group generated a cross-linked macromolecule around single AuNP through the free radical polymerization of vinyl-carrying ligands on the NP surface. As the propagation step was much faster than the decomposition of the radical initiator, each AuNP was supposed to be wrapped by a single macromolecule with functionality on the chain end introduced by the initiator. This mono-functionality provided numerous possibilities to precisely design the nanoparticle assembly or fabricate new nanocomposites. In our study, AuNPs were tethered with single carboxylic acid group, which was further converted to the vinyl group. This so-called artificial molecule was copolymerized with MMA.

[Bildunterschrift / Subline]: Schematic illustration of the synthesis of the PMMA bound polymer cage (Cage-co-PMMA).

The polymer cage, namely the cross-linked macromolecule left after etching of the AuNP core, was used for the size selective fishing process. The fishing process was demonstrated by the biphasic ligand exchange reaction. The citrate stabilized AuNPs (Ct@AuNP) were dispersed in the aqueous phase, while the polymer cage with attached PMMA chain was dissolved in the chloroform phase. After vigorous shaking, AuNPs were transferred from the aqueous phase to the chloroform phase with the help of the phase transfer catalyst tetraoctyltrimethyl ammonium bromide (TOAB). The successful ligand exchange was attributed to the numerous thiol groups of the polymer cage, as sulfur has stronger affinity to gold than the citrate ligands. The polymer cage exhibited high efficiency when extracting Ct@AuNP under 15 nm. When a mixture of Ct@AuNP in different sizes (diameter 3 nm, 15 nm, 30 nm) was involved as precursor, the polymer cage showed significantly higher size selectivity than the block copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-PVP) and the thiol-terminated PMMA (PMMA-SH). AuNPs of 30 nm in diameter were not found in the polymer cages, while PS-b-PVP and PMMA-SH extracted AuNP of all the sizes into the organic phase.
Based on the extraordinary ability of the polymer cage for size separation of metal nanoparticles, the future work is focused on varying the size of the polymer cage for discrete size separation. Moreover, the concept of the size selective “fishing” can be expanded with respect to shape and chemistry for preparing hybrid material in a single step.




Scientific Career
  • 10/2012-now
  • Ph.D., University of Bayreuth, Prof. Dr. Andreas Greiner, Macromolecular Chemistry II
  • 04/2011-10/2012
  • Master, Philipps University of Marburg, Macromolecular Chemistry
  • 04/2008-03/2011
  • Bachelor, Philipps University of Marburg, Chemistry

Scholarships and Awards
  • * DAAD Price 2009 Philipps University of Maburg
  • * Chemiefonds-Scholarship of chemical industry (02.2013-02.2015)
  • * Roche Continents (2011)