Stability assessment of indocyanine green within dextran-coated mesocapsules by absorbance spectroscopy

The biocompatibility and high absorption in the near IR range of indocyanine green (ICG) have made it a suitable candidate chromophore for optical imaging and laser-mediated therapy of superficial tumors. However, its clinical efficacy remains limited by factors such as rapid circulation kinetics, lack of target specificity, and molecular instability. Such drawbacks motivated us to encapsulate ICG into carrier particles to improve target specificity and retention time. We use absorbance spectroscopy to investigate the effects of encapsulating ICG within dextran-coated capsules. The mesocapsules (MCs) containing ICG are synthesized using a previously reported charge-assembly technique. Both freely dissolved ICG and ICG-MCs are prepared with ICG concentrations of either 50 or 10 mu g/ml. Samples are exposed either to a broadband light source or incubated at 3, 23, or 40 degrees C. Absorbance spectra are recorded at various time points up to 96 h. At the lower concentration of 10 mu g/ml, ICG within MCs experiences less light-induced degradation. The MC system also protects ICG from thermal degradation at all tested temperatures. The polymer-salt aggregate core of the MCs hinders the mobility of ICG molecules. The MC system shields ICG from vibrational and translational agitation as well as molecular changes such as fragmentation. (C) 2007 Society of Photo-Optical Instrumentation Engineers.