ELITE NETZWERK BAYERN

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Research Project

A Novel Approach to Tailoring the Size of Quasi-Spherical Gold

Nanoparticles

by Christoph Metzger (23.06.2015)

Enabling uniform growth of gold nanoparticles is challenging. However, the ability to tailor their size and shape provides a facility to determine their physical, optical and electronic properties [1] and thus allows the adaption of their morphology to a specific function. In this respect, a seed-growth approach is developed capacitating the precise definition of the final gold nanoparticle size, while their quasi-spherical shape is maintained.

Gold nanoparticles cover many fields of application ranging from catalysis [2,3], sensors [4], probes [5] and electronics [6] to therapeutic agent delivery [7] and many more. The main motives for using them in research and analysis in place of other materials are their high stability in aqueous media in conjunction with low toxicity and good surface functionalizability. The reduction of tetrachloroauric acid by trisodium citrate to form nearly monodisperse colloidal gold was first used by Turkevich et al. [8] and later refined by many researchers. This method facilitates control over the particle size in the range of 16 nm to 150 nm, however, only below 20 nm a sufficient reproducibility and a narrow particle size distribution is given. In order to counteract polydispersity as well as aspherically shaped particles toward particle diameters up to 180 nm, Bastùs et al. [9] proposed a kinetically controlled seed-growth strategy, where secondary nucleation is inhibited by the adjustment of reaction parameters.

This work embraced the seed-growth approach and furthermore aimed to precisely tailor the particle size to a prespecified diameter, while quasi-spherical shape and a narrow particle size distribution have been maintained. To this effect and in order to additionally ensure high growth rates, the original seed-growth strategy was developed further by an arithmetic approach based on the seed colloid properties. As a consequence, also the consumption of expensive chemicals could be diminished.

The reaction sequence was monitored by UV-Vis Spectrophotometry and Dynamic Light Scattering. For incremental growth steps, a red shift of the surface plasmon resonance band as well as a broadening effect was observed confirming growth of the nanoparticles. Extinction spectra recorded by UV-Vis indicated both narrow particle size distributions and a quasi-spherical shape evolution, which was substantiated by correlated Mie calculations. Due to the precise adherence to the reaction conditions nanoparticle growth progressed as calculated by the arithmetic approach.

Electrophoretic Light Scattering revealed high zeta potentials independent of the particle size, proving the excellent stability of the colloidal systems. Scanning Electron Microscopy substantiated both the quasi-spherical shape and the uniform particle size distribution of the produced gold nanoparticles up to 100 nm (see Fig. 1).

[Bildunterschrift / Subline]: Fig. 1: Scanning Electron Microscope Images of incremental growth steps

An existent seed-growth strategy is used to produce quasi-spherical gold nanoparticles of up to 180 nm in diameter, which was subsequently enhanced by an arithmetic approach. The resulting ability to tailoring the final particle size during the seed-growth synthesis in combination with a narrow particle size distribution opens a large field of size-specific applications. Gold nanoparticles synthesized this way could be further functionalized by displacing the surfactant by functional surface molecules.

Acknowledgements

The author thanks Dr.-Ing. Doris Segets, Dipl.-Ing. Ulrike Weichsel and M. Sc. Wei Lin for valuable discussions as well as their assistance with laboratory work and SEM image acquisition.

References

[1] Sun, Y.; Xia, Y. Science 2002, 5601, 2176-2179.
[2] Haruta, M.; Daté, M. Appl. Catal. A 2001, 222, 427-437.
[3] Thompson, D.T. Nano Today 2007, 2, 40-43.
[4] Ali, M.E.; Hashim, U.; Mustafa, S.; Che Man, Y.B.; Islam, K.N. J. Nanomater. 2012, 2012, Article ID 103607.
[5] Perrault, S.D.; Chan, W.C.W. P. Natl. Acad. Sci. USA 2010, 107, 11194-11199. 
[6] Huang, D.; Liao, F.; Molesa, S.; Redinger, D.; Subramanian, V. J. Electrochem. Soc. 2003, 150, G412-G417.
[7] Brown, S.D.; Nativo, P.; Smith, J.-A.; Stirling, D.; Edwards, P.R.; Venugopal, B.; Flint, D.J.; Plumb, J.A.; Graham, D.; Wheate, N.J. JACS 2010, 132, 4678-4684.
[8] Turkevich, J.; Stevenson, P.C.; Hillier, J. Discuss. Faraday Soc. 1951, 11, 55-75.
[9] Bastùs, N.G.; Comenge, J.; Puntes, V. Langmuir 2011, 27, 11098-11105.


Scientific career
  • since 2013
  • Elite Graduate Program M. Sc. Advanced Materials and Processes, Friedrich-Alexander University Erlangen-Nürnberg
  • 2009 - 2013
  • B. Eng. Surface Technology and Materials Science / Materialography, Aalen University of Applied Sciences

Scholarships and Awards
  • * Traveling Scholarship of the Max Weber-Program of the State of Bavaria (2015)
  • * Fellowship of the Leonardo-Kolleg of the Friedrich-Alexander University Erlangen-Nürnberg (2014)
  • * Scholarship of the Max Weber-Program of the State of Bavaria (2014)