Synthesis of Near-Infrared-Absorbing Nanoparticle-Assembled Capsules

Abstract

Indocyanine green (ICG) is an FDA-approved photosensitizer dye used in clinical settings for optical diagnostics and near-infrared laser-based therapy. However, the rapid clearance and nonspecific vascular plasma binding issues impede ICG performance. Encapsulating ICG within a colloidal matrix is a potential approach to solving these problems, but thus far, there has been limited success. A new strategy, based on the nanoparticle assembly synthesis of stable, non-liposomal nanoparticle/polymer microcapsules, to encapsulate ICG is presented. Nanoparticle-assembled capsules (NACs) are prepared at room temperature, in aqueous solution, and at neutral pH by combining a polyallylamine solution, a phosphate solution, and an aqueous sol of silica nanoparticles; ICG-containing NACs with 0.6−1.0 μm diameter are prepared by adding an ICG solution before the nanoparticle sol. ICG loading is readily controlled with an attainable maximum loading of ∼23 wt %. There is negligible leakage from the capsules after 24 h at room temperature in phosphate buffer saline solution, with 17% ICG leakage after 8 h at 37 °C. ICG-containing NACs are capable of heat generation in response to near-infrared laser irradiation and are stable to multiple photothermal heating cycles. Fibroblast cells exposed to these capsules remain viable after 2 days of incubation. ICG-containing NACs are a promising material for new photothermal therapy applications and are illustrative of a new approach for encapsulating organic dye compounds.