Theranostic microparticles manufactured through Layer by Layer functionalisation

Cancer is considered the leading cause of death and estimates assess that the new tumor cases will rise to 20.3 million per year with 13.2 deaths by 2030. For improving drug delivery, pharmaco-kinetics, bio-distribution and real-time tracking, the past decade research has been focusing into the development of new theranostic systems able to combine a therapeutic compound with an imaging probe in the same vehicle, able to selectively target cancer cells. In this work we developed microcapsules, combining the bioimaging properties of excitation-dependent fluorescent graphene quantum dots (GQDs) with therapeutics-loaded microparticles functionalized by electrostatic Layer by Layer (LbL), using calcium carbonate (CaCO3) core as template. This approach is suitable for drug encapsulation in the core as well as incorporation of biomolecules in the coating as an attractive multi-modal strategy able to be tracked in vivo and real time. LbL technology has been widely studied and used in many different fields such as optics, electronic, biology and medicine thanks to its simplicity and versatility. Moreover, semiconductor Quantum Dots (QDs) have emerged as an interesting tool for bioimaging purposes but they presented biocompatibility lack. Recently carbon-based quantum dots have been discovered and applied as imaging probes to replace semiconductor QDs, thanks to their strong fluorescence, water and photo-stability and, mainly, high cytocompatibility. Therefore, in this work GQDs produced from green route, were adopted. Their morphology, physico-chemical and optical properties have been analysed via Transmission Electron Microscopy (TEM), Zeta-potential, Fourier Transform Infrared Spectroscopy (FTIR-ATR), X-ray Photoelectron Spectroscopy (XPS) and UV-Visible (UV-Vis), showing round-shaped structure, negative surface charge and excitation-dependent emission. Moreover, it was assessed their cytocompatibility via Live/Dead and Presto Blue assays, with high fibroblast viability up to 500 µg/mL concentration and cells ability to internalize the nanoparticles even at low concentration (50 µg/mL). Then, CaCO3 microparticles have been synthetized starting from calcium chloride (CaCL2) and sodium carbonate (NaCO3) reagents, optimizing the process in order to stabilize the CaCO3 vaterite form, to avoid the transformation into calcite (more stable water suspension). To tackle this challenge 1 mg/mL of poly(styrenesulfonate) (PSS) was added to the reagents .Then, the manufactured particles were used as sacrificial template for the deposition of two biocompatible polyelectrolytes, Poly(allylamine hydrochloride) (PAH) (positively charged) and PSS (negatively charged), via LbL technique to create a nanocoating (shell) surrounding the inner CaCO3 particle (core). Subsequently, the GQDs were incorporated within the nanocoating after dissolution in PSS. The morphology and final size were investigated via Scanning Electron Microscopy (SEM) as well as the optical properties by using the Confocal Microscope. Following the LbL coating step, the CaCO3 core was dissolved in EDTA solution leaving the polyelectrolyte shell to obtain a hollow microcapsule interesting for further investigations regarding drug loading and delivery tests. Furthermore, as proof of concept, during the last period of the project we reduced the particles size, in order to reach the nanoscale. By dissolving the reagents in Glycerol (83.3% V/V) an average diameter of 700 nm was achieved.