Layer-By-Layer Nanoparticles for Delivery of Second Window Near-Infrared Probes in Vivo

Second window near-infrared (NIR-II) imaging provides fluorescence-based anatomical information deep to skin as NIR-II light (1000 nm to 1700 nm) features deep tissue penetration, reduced tissue scattering, and negligible tissue autofluorescence. NIR-II fluorescence imaging probes; including down-conversion particles, quantum dots, single-walled nanotubes, and organic dyes, are formulated in biocompatible layer-by-layer (LbL) nanoparticles. 150 - 200 nm size range is obtained and hyaluronic acid is used as outer layer for extended blood circulation. Systemic delivery of LbL nanoparticles in Balb/c mice demonstrates that down-conversion particles have least autofluorescence due to its relative longer emission wavelength (>1500 nm). Organic dyes with emission at 1100 nm show most autofluorescence and elevated tissue scattering. Both quantums dots and single-walled nanotubes give moderate autofluorescence and tissue scattering. Pharmacokinetics studies of the LbL probes indicate that layer-by-layer formulation extends the blood circulation with half-life from 14 ~ 23 hrs. Tissue histology suggests none of the LbL probes present major toxicity. A further imaging involving orthotopic ovarian tumor is conducted using down-conversion particles due to its relative low autofluorescence. At 96 hrs, tumor is visualized in deep intraparatoneal cavity with high resolution. In this work, we present a first example of head-to-head comparison of all current NIR-II probes using LbL formulation. In vivo imaging performance is evaluated and suggests NIR-II imaging is versatile and robust technique for biomedical applications.