(97a) The Kinetically-Controlled Formation of Biodegradable Gold Nanoclusters

Gold nanoparticles which exhibit surface plasmon resonance in the near-infrared region (NIR) of the optical spectrum have been found to be extremely useful for biomedical imaging applications1. These imaging agents, however, must eventually be cleared from the body. Clearance has been shown to be highly dependent by the size of imaging contrast agents, and current imaging agents typically exceed the clearance requirement of approximately 5 nm in diameter2.

We have developed clusters of 4 nm gold nanoparticles which are less than 100 nm in diameter and possess the ability to biodegrade. UV-visible NIR spectroscopy indicates that these nanoclusters present strong absorbance at 650 to 900 nm. The nanoclusters biodegrade over a week into particles of small enough for efficient clearance. Cluster formation was induced by the addition of a polymer templating agent. Primary particles were capped with different ligands in order to prevent uncontrolled aggregation. Hyperspectral microscopy, darkfield reflectance imaging and transmission electron microscopy (TEM) confirmed that the nanoclusters biodegrade in macrophage cells as well as in solution.

ζ-potential measurements have also been conducted on clusters and deaggregated particles in order to approximate surface charge and electrostatic forces. The results can be described with DLVO theory. Calculated and experimental stability ratios as well as calculated interaction potentials have been used to develop a mechanism for the formation and degradation of biodegradable nanoclusters. In conclusion, biodegradable nanoclusters were formed and the mechanism of formation of these kinetically-controlled clusters was investigated.

(1) Anker, J.N., et al. Biosensing with plasmonic nanosensors. Nature Materials 7 (2008) 442-453

(2) Choi, H.S.. et al. Renal clearance of quantum dots. Nature Biotechnology 25 (2007) 1165-1170