Quimica

6504

Langmuir 2007, 23, 6504-6509

Articles
Hydrogel-Templated Growth of Large Gold Nanoparticles: Synthesis of Thermally Responsive Hydrogel-Nanoparticle Composites
Jun-Hyun Kim and T. Randall Lee*
Department of Chemistry, UniVersity of Houston, 4800 Calhoun Road, Houston, Texas 77204-5003 ReceiVed October 4, 2006. In Final Form: March 30, 2007
In this paper, we describe a uniquestrategy for preparing discrete composite nanoparticles consisting of a large gold core (60-150 nm in diameter) surrounded by a thermally responsive nontoxic hydrogel polymer derived from the polymerization of N-isopropylacrylamide (NIPAM) or a mixture of NIPAM and acrylic acid. We synthesize these composite nanoparticles at room temperature by inducing the growth of gold nanoparticles in the presenceof preformed spherical hydrogel particles. This new method allows precise control of the size of the encapsulated gold cores (tunable between 60 and 150 nm) and affords composite nanoparticles possessing diameters ranging from as small as 200 nm to as large as 550 nm. Variable-temperature studies show that the hydrodynamic diameter of these composite nanoparticles shrinks dramatically when thetemperature is increased above the lower critical solution temperature (LCST); correspondingly, when the temperature is lowered below the LCST, the hydrodynamic diameter expands to its original size. These composite nanoparticles are being targeted for use as optically modulated drug-delivery vehicles that undergo volume changes upon exposure to light absorbed by the gold nanoparticle core.Introduction
The development of new synthetic routes to nanometer-scale particles continues to be driven by the potential applications offered by their unique optical properties.1 In particular, research focused on nanoparticle fabrication is urgently needed to develop new nanoscale materials and devices for controlled drug delivery.2 Of particular interest is the ability of metal nanoparticles toabsorb or scatter light; for many optical applications, nanoparticles are superior to molecular chromophores.3 Research in this area has largely focused on metal nanoparticles (e.g., silver, copper, and gold) because of their ease of fabrication and their strong optical absorbances.4-6 Gold nanoparticles have drawn particular attention due to their biocompatibility, which makes them attractive for usein vivo as nanoscale biomaterials.7-8 Colloidal gold nanoparticles are often decorated with organic molecules, inorganic materials, or polymers to facilitate their use in catalysis, photonics, electronics, optics, and biomedicine.9-11 While a number of methods have been described for the preparation of polymer-coated gold nanoparticles,11-16 these
* To whom correspondence should be addressed.E-mail: trlee@uh.edu.
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studies have utilized either polymers that contain strong...