Optimization of the Synthesis Procedure and Characterization of Small Indocyanine Green (ICG) J-aggregates

Indocyanine green (ICG) dye J-aggregates are stable assembly of ICG fluorophores into micron scale nanoparticles. The spectral properties of these aggregates make them ideal for labelling and imaging of biological structures in-vivo using photoacoustic imaging modality. However, controlling the formation of this aggregation system is complicated since this is a self-assembling system. Furthermore, one complication with the self-assembling process is to control the size of the formed ICG J-aggregates since this defines its biodistribution and delivery effectiveness when crossing biological barriers such as the blood–brain barrier (BBB). Therefore, a robust parotocol that can adjust the parameters of the aggregation system to produce small ICG J-aggregates is critically needed This project has for main goal to improve the protocol designed to ease the production of small ICG J-aggregates and help with their characterization toward translational applications.

Note: This project is part of the BENG395 course

Hi, my name is Leandro Soto, and I am a Bioengineering undergrad at George Mason University. During this summer URSP I have been working at Dr. Veneziano’s lab.

For my project I used an FDA-approved organic dye to form small ICG J-aggregates that can be used for photoacoustic imaging.

In chemistry, an aggregate can be defined as a dense collection of massive particles, which possess a strong bonding. Now when we talk about dye aggregates, we refer to a phenomenon where dye molecules or ions bound by electrostatic interaction (Van der Waals forces) in a solution. J-aggregates are defined as a specific dye complex of molecules held together by noncovalent bonds.

These J-aggregates are characterized by an absorption band that presents a change of spectral band position in the absorption of the aggregates to a longer wavelength (bathochromic shift) compared to the relevant monomer band.

The redshift peak of a dye monomer is 780 nanometers while the J-aggregates have an absorption maximum peak at 895 nanometers. Since these probes do not have energetic dissipation from fluorescence when excited to near infrared laser, they can be used for photoacoustic imaging due to their strong absorption in the near infrared region (NIR-I region).

It is worth to mention that besides their usefulness as a great contrast agent and good photothermal stability, ICG J-aggregates also have great biocompatibility which facilitates the in-vivo photoacoustic imaging.

In general, any manipulation of these aggregates is done by altering the components of a sample other than the chemical constituent of interest and not to the aggregates themselves.

During this summer URSP program my project focused on optimization of the synthesis procedure and characterization of an already developed protocol to make small ICG J-aggregates by changing the parameters and conditions in which the samples were prepared. Although I cannot share my results at the time due to a pending patent, I can say that the overall process was successful.

Some of their future applications can involve the development of multifunctional supramolecular complexes that not only generate a deeper tissue imaging, but they also can be used as delivery mechanism to targeted cells or tissues.