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Preliminary results show that 65% of a mix of spherical38 and rod-shaped particles inserted are recovered in different fractions, which show a clear separation of the particles according to their shape

Separation of nanoparticles by gel electrophoresis according to size and shape.

NANO LETTERS, no. 9 (2007): 2881-2885

Cited by: 313|Views20
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Abstract

We demonstrate the separation of gold and silver nanoparticles according to their size and shape by agarose gel electrophoresis after coating them with a charged polymer layer. The separation is monitored optically using the size- and shape-dependent plasmon resonance of noble metal particles and confirmed by transmission electron microsc...More

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Introduction
  • The authors demonstrate the separation of gold and silver nanoparticles according to their size and shape by agarose gel electrophoresis after coating them with a charged polymer layer.
  • The mobility of silver and gold spheres of the same size are comparable (Supporting Information, Figure S2a).
Highlights
  • We demonstrate the separation of gold and silver nanoparticles according to their size and shape by agarose gel electrophoresis after coating them with a charged polymer layer
  • An alternative to the high-yield synthesis of nanoparticles with ultranarrow size distribution is the postsynthetic separation of particles similar to cleaning procedures in organic synthesis
  • We show here how the technique of gel electrophoresis is successfully used to separate nanoparticles according to size and shape
  • We separate polymer-coated spherical, rodshaped, and triangular gold and silver nanoparticles, which show strong colors induced by plasmon resonances
  • The Henry formula, corrected for the thickness of the PEG layer, allows us to interpret qualitatively and quantitatively the measured mobilities without taking into account any gel matrix effects. This seems justified by the fact that we are using very low agarose gel concentrations (<0.5%) giving pore diameters in the gel (L ) 200-400 nm),[37] considerably larger than the size of the spherical particles. In support of this argument, we find that higher gel concentrations lead to worse separation (Supporting Information, Figure S4), probably due to increased particle/matrix interactions
  • Preliminary results show that 65% of a mix of spherical[38] and rod-shaped particles inserted are recovered in different fractions, which show a clear separation of the particles according to their shape (Supporting Information, Figure S5)
Results
  • The fact that the observed sizes averaged over all fractions agree well with the mean sizes of the triangles, spheres, and rods measured on the original sample (Supporting Information, Figure S1 and vertical lines in Figure 3c) shows again the reliability of the sampling and the self-consistency of the results.
  • For gold spheres (L ≈ 20 nm, British Biocell International, BBI) carrying the four types of end groups, the authors compare the electrophoretic mobilities measured in agarose gels with values determined by dynamic light scattering (DLS, using a Zeta Sizer Nano ZS90, Malvern Instruments).[29,30] The results show reasonable agreement within the errors (Figure 4b).
  • From the mobility -1.148 μm cm/Vs of the medium fraction of silver spheres (2a ) 50 nm), which is corrected for the electro-osmotic effect (+0.315 μm cm/Vs), the authors obtain a density of 8 charged PEG molecules per 100 nm[2] on the particle surface.
  • As the mobility of particles in a gel is strongly depending on the surface charge density, it would be interesting to compare the PEG packing density for particles of different sizes.
  • Because a saturation of the mobility is observed when the proportion of SH-PEG-COOH to SH-PEG-OCH3 is greater than 75% (Supporting Information, Figure S3, probably due to proximity effects), the overall density of attached PEG molecules is estimated to be about 23 per 100 nm[2].
  • Preliminary results show that 65% of a mix of spherical[38] and rod-shaped particles inserted are recovered in different fractions, which show a clear separation of the particles according to their shape (Supporting Information, Figure S5).
Conclusion
  • The authors find values for the charge density of PEG coated gold and silver nanoparticles, the number of attached PEG molecules per surface area, the PEG layer thickness, and the gel surface potential.
  • Supporting Information Available: Figures showing the composition of the silver nanoparticle sample, the mobility of gold and silver spheres (BBI) coated with different SHPEG-X, the mobility of silver particles as a function of the fraction of SH-PEG-COOH, the influence of gel concentration on separation efficiency, and preliminary results on upscaling the separation with a vertical column.
Funding
  • Dr Florian Banhart for help with electron microscopy, and we acknowledge financial support by the DFG under the Emmy Noether program. Supporting Information Available: Figures showing the composition of the silver nanoparticle sample, the mobility of gold and silver spheres (BBI) coated with different SHPEG-X, the mobility of silver particles as a function of the fraction of SH-PEG-COOH, the influence of gel concentration on separation efficiency, and preliminary results on upscaling the separation with a vertical column
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