Gold Nanoclusters with Strong near Infrared Absorbance for Biomedical Imaging

We have developed small 40-50 nm gold nanocluster NIR imaging agents, stabilized by carboxymethyldextran (CMD) The shape asymmetries and the closely spaced primary particles within the clusters  produce a strong near infra red (>800 nm) absorbance via a surface plasmon resonance (SPR), as a result of multipole interactions. The cluster size was characterized by dynamic light scattering(DLS) and TEM, whereas the quantity of polymer was determined by Thermogravimetric analysis. We develop a theory to explain the synthesis of these particles based on nucleation, clustering and growth upon reduction of a Au precursor in the presence of CMD. Molecular imaging of plaque in coronary arteries before rupture is a crucial step in treating atherosclerosis. These particles are preferentially engulfed by macrophages associated with vulnerable plaque due to the CMD associated with the particles. The particles also exhibit multi-photon luminescence and hence the plaque can be imaged by multi-photon microscopy.