Synthesis and characterization of Ag2S based nanoparticles as luminescence nanothermometers

• Autores: Diego Ruiz Gómez
• Directores de la Tesis: Beatriz Hernández Juárez (dir. tes.), Daniel Jaque García (tut. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2019
• Idioma: español
• Tribunal Calificador de la Tesis: Ángel Millán Escolano (presid.), Dirk Ortgies (secret.), Benito Jorge Rubio Retama (voc.)
• Programa de doctorado: Programa de Doctorado en Materiales Avanzados y Nanotecnología por la Universidad Autónoma de Madrid
• Materias:
  • Física
    • Química física
      • Química de coloides
    • Unidades y constantes
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • The study and applications of semiconductor nanoparticles (NPs) have grown in the last 30 years due to their attractive and exceptional optical and electronic properties. Their highly efficient photo- and electroluminescence is tunable in a wide range of the electromagnetic spectrum, allowing the preparation of NPs with an emission centered form the UV to the mid infrared range. Their reduced size is one of the attractive features for some applications in biology such as drug-delivery or selective bio-labelling. Due to their small size (comparable to that of proteins or nucleic acids), semiconductor NPs can be coupled to biological molecules and with them reach the inside of cells, what has been vastly developed for fluorescent optical tracking both in vitro and in vivo. The high absorption and scattering of biomolecules and tissues in the visible range has trigger the search of other non-toxic NPs whose optical response is centered in the first or second biological windows (also called NIR-I and NIR-II, respectively), NIR spectral ranges where light extinction is minimized. In this way, some NIR NPs can result in higher spatial resolution, deeper tissue penetration, and improved overall image quality. Silver sulfide (Ag2S) based NPs have been appointed as one of the most promising materials since they are not toxic and their photoluminescence centered in the NIR region. The easy preparation of bright NPs with a photoluminescence centered in the region called NIR-II (1000-1400 nm) triggered their use in many biological assays with positive results in imaging, targeting and therapy experiments with negligible toxicity making this material more adequate than other semiconductors like Pb or Hg chalcogenides. In Chapter 2 it is described how these appealing properties are taken advantage by adding a previously not studied property: their capability to be used as luminescence thermometers (LThs) in the NIR-II range. The as-synthesized NPs were thoroughly characterized and transferred to water using a newly developed one-step procedure. This ligand exchange step preserves their thermometric sensitivity as evidenced in their use for the in vivo monitoring of the temperature change in a mouse’s brain during a heating/cooling experiment. Furthermore, these previously described routes are found to produce NPs with a dense surface coating and embedded in the silver precursor formed in the course of the synthesis reaction. In Chapter 3, a new synthetic route is developed to obtain NPs with a lighter surface coating that allow for a more versatile and efficient ligand exchange procedure. Moreover, the preparation of monodisperse individual NPs using this new route allows for the preparation of other structures based on Ag2S NPs: Ag2S/Ag2(S,Se) and Ag2S/Ag2(S,Se)/ZnS core/shell NPs. Both structures show higher PLQY and improved stability towards oxidation while retaining their labile surface that allows the easy tuning of their surface chemistry. In the case of the CS NPs their surface can be coated with different biocompatible polymers and even with oligonucleotides, biomolecules that may be biologically active allowing the targeting of specific sequences. In Chapter 4, the preparation of multifunctional composites is explored using two different approaches. These composites consist on a single nanostructure able to simultaneously produce hyperthermia (either optical or magnetic) and provide temperature reading to prevent undesired damage in healthy zones. The correct formation of these composites is achieved by the encapsulation of Iron Oxide Superparamagnetic Nanoparticles (SPIONs) and Ag2S-based NPs inside a sphere formed by a stack of bilayers of a polyethylene glycol modified phospholipid. These liposomes, with a hydrodynamic size of around 100 nm are of an ideal size for their use in living organisms. Incipient cell culture studies suggest their correct internalization in cells, opening the door for simultaneous heating and temperature control in cancer cells.