Size-tunable ICG-based contrast agent platform for targeted near-infrared photoacoustic imaging.

Near-infrared photoacoustic imaging (NIR-PAI) combines the advantages of optical and ultrasound imaging to provide anatomical and functional information of tissues with high resolution. Although NIR-PAI is promising, its widespread use is hindered by the limited availability of NIR contrast agents. J-aggregates (JA) made of indocyanine green dye (ICG) represents an attractive class of biocompatible contrast agents for PAI. Here, we present a facile synthesis method that combines ICG and ICG-azide dyes for producing contrast agents with tunable size down to 230 nm and direct functionalization with targeting moieties. The ICG-JA platform has a detectable PA signal in vitro that is two times stronger than whole blood and high photostability. The targeting ability of ICG-JA was measured in vitro using HeLa cells. The ICG-JA platform was then injected into mice and in vivo NIR-PAI showed enhanced visualization of liver and spleen for 90 min post-injection with a contrast-to-noise ratio of 2.42.

Automated summary

Near-infrared photoacoustic imaging (NIR-PAI) combines optical and ultrasound imaging to provide high-resolution anatomical and functional information of tissues. However, the limited availability of NIR contrast agents hinders its widespread use. J-aggregates (JA) made of indocyanine green dye (ICG) are a promising type of contrast agents for PAI. In this study, we present a simple synthesis method that combines ICG and ICG-azide dyes to produce contrast agents with tunable size and targetability. The ICG-JA platform exhibits a strong PA signal in vitro and enhanced visualization of liver and spleen in vivo.