Quantitative evaluation of nanoshells as a contrast agent for optical coherence tomography

Abstract

Optical coherence tomography (OCT) has emerged as a powerful imaging tool for a variety of biomedical applications. Methods to enhance contrast in OCT images, including gold nanoshells, have been explored recently. Gold nanoshells are a novel type of nanoparticle composed of a silica core and a thin gold shell. By varying the relative dimensions of core and shell, the optical resonance of these nanoshells can be precisely and systematically varied over a broad wavelength region ranging from the near-UV to the mid-infrared. For this study, we designed and constructed nanoshells expected to have low absorption and high scattering for OCT at 1310 nm. We then conducted measurements to elucidate the effects of nanoshell core and shell size, nanoshell concentration, and tissue scattering coefficient on OCT image enhancement (i.e. intensity gain) by nanoshells. These measurements were performed with nanoshells suspended in water and in a variety of tissue phantoms. Increasing nanoshell core and shell size tends to increase the calculated backscattering coefficient, and thus increases OCT intensities by 2-7 dB in a tissue phantom with a biologically relevant scattering coefficient. Increasing nanoshell concentration also increases OCT intensities, however a minimum of 10⁹ nanoshells/mL is needed for appreciable enhancement in the tissue phantom. The intensity gain from one size of nanoshells varies between 5 and 9 dB depending on the scattering coefficient, with intensity gains decreasing as scattering increases. These results provide the first quantitative measurements of the effects of nanoshells to enhance OCT imaging at 1310 nm.