Enhanced photo-stability, thermal-stability and aqueous-stability of indocyanine green in polymeric nanoparticulate systems

Photo-degradation, thermal-degradation and aqueous-instability of indocyanine green (ICG) limits its application as a fluorescence contrast agent for imaging purposes. Thus, the objective of this study is to develop polymeric nanoparticles entrapping ICG and to establish its effectiveness in providing photo-stability, thermal stability and aqueous stability to ICG. Nanoparticles entrapping ICG were engineered, characterized and the degradation kinetics of ICG in the nanoparticles was investigated in aqueous media. The entrapment of ICG in the nanoparticles causes a shift in its wavelength of peak fluorescence and a decrease in its peak fluorescence intensity. The degradation of ICG in aqueous nanoparticle suspension followed first-order kinetics for the time period studied. ICG entrapment in the nanoparticles enhanced aqueous-stability of ICG (half-life, t1/2 was 72.2 ± 6.1 h for ICG in the nanoparticles as compared to 16.8 ± 1.5 h for free ICG solution), photo-stability of ICG (t1/2 was 73.7 ± 7.5 h for ICG in the nanoparticles as compared to 14.4 ± 2.4 h for free ICG solution when exposed to room light from two 32 W normal fluorescent tubes) and thermal-stability of ICG (t1/2 of ICG at 42 °C was 62.4 ± 1.7 h for ICG in the nanoparticles as compared to 10.1 ± 0.6 h for free ICG solution).