New fluorescent nanovesicles by self-assembly of organic fluorophores, sterols and surfactants as probes for bioimaging

Student thesis: Doctoral thesis


Finding new fluorescent organic nanoparticles (FONs) with the potential to overcome the limits of common fluorescent probes as molecular fluorophores, fluorescent proteins and inorganic nanoparticles is a subject of strong interest for materials scientists developing new probes for fluorescence microscopy and theranostics. In the recent years, innovative non-liposomal nanovesicles, based on the self-assembly of quaternary ammonium surfactants and sterols, named Quatsomes (QSs), have been developed as promising candidates for applications as multifunctional drug carriers. Within this scenario, the main objective of this Thesis (conducted in the framework of the Marie Skłodowska-Curie ITN “Nano2Fun”) is to explore the possibility of using Quatsomes as a vehicle for nanostructuring in aqueous media several dye molecules, irrespective of their physicochemical and optical properties, in order to obtain new fluorescent organic nanoparticles (FONs) with superior colloidal stability and enhanced fluorescent features, especially with high brightness, in relation to single molecule flurofores and other type of FONS. The self-assembly of molecular organic fluorophores, sterols and quaternary ammonium surfactants into fluorescent Quatsomes was achieved by the DELOS-SUSP method, a compressed CO2 –based process which guarantees a highly homogeneous membrane composition and supramolecular arrangement, which have impact on the optical properties of the obtained FONs. Different strategies have been explored to nanostructurate in aqueous media, by mean of QSs, molecular dyes with different physicochemical properties, including those water- and non-water soluble, analyzing the impact of their nanostructuration on the optical properties of the obtained FONs. Thus, anionic water-soluble dyes, such as fluorescein, were nanostructured over QSs surface, taking advantage of anionic/cationic interaction among dye and vesicles surface. On the other hand, lipophilic and non-water soluble dyes modified with long alkyl chains can be stably incorporated into QSs membrane, as shown in the case of several dyes families, including cyanine, diketopyroolopyrrole (DPPs) and fluorene derivatives. The fluorescent QSs showed superior colloidal and optical stability (up to several months), a high degree of structural homogeneity and high fluorescence performances, overcoming those of other nanostructures of the same dyes. Furthermore, aiming to obtain multicolor nanoparticles, Quatsomes allowed the simultaneous loading within their membrane of different dyes, which showed a highly efficient fluorescence resonance energy transfer (FRET) mechanism, an interesting tool for monitoring the carrier integrity during the drug delivery and for multiplexed imaging applications. Finally, fluorescent Quatsomes were tested as nanoprobes for in vitro cells imaging. It has been demonstrated that fluorene-based Quatsomes (named LysoQS) constitute a strongly specific lysosomal probe ideal for long-term imaging. Furthermore, cyanines-loaded Quatsomes were used as probes for super-resolution microscopy technique (STORM) which allowed visualizing and resolving single Quatsomes structures upon internalization in cells. The results of this Thesis showed that fluorescent Quatsomes, thanks to the advantages offered in comparison with other commonly employed fluorescent labels, constitute a promising fluorescent nanoprobes with possible future applications in bioimaging, theranostics and, generally, nanomedicine.

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Date of Award28 Apr 2017
Original languageEnglish
SupervisorJaume Veciana Miró (Director), Nora Ventosa (Director) & Roser Pleixats Rovira (Director)

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