Interactions of Indocyanine Green and Lipid in Enhancing Near-Infrared Fluorescence Properties: The Basis for Near-Infrared Imaging in Vivo

Abstract

Indocyanine green (ICG) is a near-infrared (NIR) contrast agent commonly used for in vivo cardiovascular and eye imaging. For medical diagnosis, ICG is limited by its aqueous instability, concentration-dependent aggregation, and rapid degradation. To overcome these limitations, scientists have formulated ICG in various liposomes, which are spherical lipid membrane vesicles with an aqueous core. Some encapsulate ICG, while others mix it with liposomes. There is no clear understanding of lipid–ICG interactions. Therefore, we investigated lipid–ICG interactions by fluorescence and photon correlation spectroscopy. These data were used to design stable and maximally fluorescent liposomal ICG nanoparticles for NIR optical imaging of the lymphatic system. We found that ICG binds to and is incorporated completely and stably into the lipid membrane. At a lipid:ICG molar ratio of 250:1, the maximal fluorescence intensity was detected. ICG incorporated into liposomes enhanced the fluorescence intensity that could be detected across 1.5 cm of muscle tissue, while free ICG only allowed 0.5 cm detection. When administered subcutaneously in mice, lipid-bound ICG in liposomes exhibited a higher intensity, NIR image resolution, and enhanced lymph node and lymphatic vessel visualization. It also reduced the level of fluorescence quenching due to light exposure and degradation in storage. Lipid-bound ICG could provide additional medical diagnostic value with NIR optical imaging for early intervention in cases of lymphatic abnormalities.

Erythrocyte-derived nano-probes functionalized with antibodies for targeted near infrared fluorescence imaging of cancer cells

“…Encapsulation into nano-sized structures has been investigated as an approach to shield ICG from non-specific interactions with plasma proteins, and extend its circulation time. To-date, ICG has been encapsulated into various nano-sized constructs including those composed of micelles, liposomes, synthetic polymers [12][13][14][15], calcium phosphate [16], and silica and silicate matrices [17,18]. We have previously reported on encapsulation of ICG into polymeric nanoparticles, coated with poly ethylene glycol (PEG), as a technique to increase the blood circulation time of ICG and delay its hepatic accumulation for up to an hour [19].…”

Photoacoustic imaging of tumor targeting with riboflavin-functionalized theranostic nanocarriers

“…12,13 The encapsulation of ICG in liposomes showed a significant improvement of its circulation lifetime, stability, and optical properties in vivo. 4,7,[14][15][16] Thus, ICG-loaded liposomes are a promising platform for the functionalization with targeting agents to improve their tumor binding, retention, and cellular uptake and for future conception of theranostic nanomedicines.…”

Real-Time Fluorescence Image-Guided Oncologic Surgery

“…ICG can be excited at 780 nm and the fluorescence is captured around 810 – 830 nm (Kraft and Ho, 2014). In blood, ICG interacts with lipids and plasma proteins which enhance its NIR fluorescence and increase its hydrodynamic diameter (Kraft and Ho, 2014).…”

“…ICG can be excited at 780 nm and the fluorescence is captured around 810 – 830 nm (Kraft and Ho, 2014). In blood, ICG interacts with lipids and plasma proteins which enhance its NIR fluorescence and increase its hydrodynamic diameter (Kraft and Ho, 2014). This allows ICG to remain in circulation for a longer duration and accumulate in tumor via the enhanced permeability and retention effect, before being cleared through the liver (Vahrmeijer, et al, 2013).…”