Characterisation of plasmonic copper sulphide nanocrystals containing solid lipid nanoparticles and determination of their concentration

Inorganic nanocrystals (NCs) based nanovectors offer the potential for new and innovative drug delivery systems for a targeted transport of drugs towards tissues affected by most aggressive disease including cancer. Diagnostic and therapeutic applications require, for both in-vitro and in-vivo investigation, the determination of the maximum cellular dose of these nanovectors [1] that is also mandatory for any regulatory approval [2]. Accurate determination of the nanovector concentration is not a trivial issue and currently there is a lack of experimental methods recognized as general and reliable [3]. In this work, we propose an approach for the determination of the concentration of a solid lipid nanoparticle (SLN) nanovector encapsulating photoactive copper sulfide (Cu2-xS) NCs characterized by a tunable localized surface plasmon resonance (LSPR) in the biological transparent near-infrared (NIR) spectral region for photothermal therapy. Here, Cu2-xS NCs with a narrow size distribution and an intense LSPR in the second biological window have been synthesized by hot injection method and they have been encapsulated into SLN prepared by a hot homogenization technique using a mixture of lipids, triglycerides and phospholipids. A calculation method based on Mie-Drude theory using as input data resulting from spectroscopic and dimensional investigation for the Cu2-xS NCs and NCs containing SLNs has been successfully implemented and applied for the determination of the nanovector concentration. The results are in agreement with experimental data and the proposed approach hold a great potential for determining the concentration of plasmonic NCs based nanovectors.