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Article

Charge-Driven Flocculation of Poly(l-lysine)Gold Nanoparticle Assemblies Leading to Hollow Microspheres

Supporting Info

Vinit S. Murthy,^† Jennifer N. Cha,^§ Galen D. Stucky,*^§ and Michael S. Wong*^†^‡;

Contribution from the Department of Chemical Engineering, MS-362, Department of Chemistry, Rice University, Houston Texas 77251-1892, and Department of Chemistry and Biochemistry and Materials Department, University of California, Santa Barbara California 93106

J. Am. Chem. Soc., 2004, 126 (16), pp 5292–5299

DOI: 10.1021/ja038953v

Publication Date (Web): April 3, 2004

†

Department of Chemical Engineering, Rice University.

Department of Chemistry and Biochemistry, UCSB.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

Department of Materials, UCSB.

‡

Department of Chemistry, Rice University.

, mswong@rice.edu, ; , stucky@chem.ucsb.edu

Abstract

An unusual aggregation phenomenon that involves positively charged poly(l-lysine) (PLL) and negatively charged gold nanoparticles (Au NPs) is reported. Discrete, submicrometer−sized spherical aggregates are found to form immediately upon combining a PLL solution with gold sol (diameter ≈ 14 nm). These PLL−Au NP assemblies grow in size with time, according to light scattering experiments, which indicates a dynamic flocculation process. Water-filled, silica hollow microspheres (outer diameter ≈ microns) are obtained upon the addition of negatively charged SiO₂ NPs (diameter ≈ 13 nm) to a suspension of the PLL−Au NP assemblies, around which the SiO₂ NPs form a shell. Structural analysis through confocal microscopy indicates the PLL (tagged with a fluorescent dye) is located in the interior of the hollow sphere, and mostly within the silica shell wall. The hollow spheres are theorized to form through flocculation, in which the charge-driven aggregation of Au NPs by PLL provides the critical first step in the two-step synthesis process (“flocculation assembly”). The SiO₂ shell can be removed and re-formed by decreasing and increasing the suspension pH about the point-of-zero charge of SiO₂, respectively.

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