Abstract
Solid lipid nanoparticles (SLNs) have shown great capabilities for drug delivery and are therefore attractive theranostic candidates when labelled with an imaging contrast agent. This work aims to create the first SLNs labelled for photoacoustic (PA) imaging by encapsulating a specially designed and near-infrared absorbing BODIPY dye (BY-aniline-Palm) into SLNs of dexamethasone palmitate. A one-pot formulation protocol enabled us to replace the prodrug by the BY-aniline-Palm label in various proportions up to 100%. Increasing the dye content exhibited complex but gradual transformations of the SLNs in terms of optical absorption and PA spectra, and the formation of aggregates at high concentration. A comprehensive and quantitative PA spectrometric study revealed a photoacoustic generation efficiency (PGE) that is spectrally varying and notably greater than 1. A joined spectral decomposition of the absorption and PA spectra into a sum of three Gaussian functions displayed a per-band evolution of the PGE when the concentration of BY-aniline-Palm varied and showed an interplay between the bands with a constant spectrum area. Finally, a novel quantitative PA spectroscopic approach, involving measurements at three different ambient temperatures, demonstrated that the remarkable PGE values arise from a significant thermo-elastic expansion of the SLN during the PA signal generation independently of the absorption band. This study highlights that labeled SLNs are promising agents for PA imaging and also unveils complex transformations that can occur in such nanosystems with a dye prone to aggregation.
Supplementary materials
Title
Supplementary information for Photoacoustic and Optical spectral transformations in Solid Lipid Nanoparticles labelled with an increasing concentration of NIR BODIPY
Description
Material and methods and results for the nanoparticle characterization and additional optical and photoacoustic spectra.
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