The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Monolayer Protected Clusters: Electrostatics, Stability and Applications

Timo Laaksonen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Chemical Technology for public examination and debate in Auditorium K at Helsinki University of Technology (Espoo, Finland) on the 10th of August, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8886-1)   [2298 KB]
Dissertation is also available in print (ISBN 978-951-22-8885-4)

Abstract

Monolayer protected clusters (MPCs) have become one of the most actively researched areas in chemistry. They have the potential to be the next step in creating building blocks for future highly miniaturised electric devices and could be used in biosciences as effective drug carriers and sensors. This thesis showcases some physico-chemical aspects and applications of these particles and attempts to provide tools and ideas for further research in this expanding field.

In this thesis, electrochemical studies showed that MPCs can have as many as 15 distinctive charge states and that even a HOMO-LUMO gap can be measured at room temperature for sufficiently small nanoparticles. Self-assembled monolayers on the nanoparticle surface were shown to be ion permeable, and this can radically affect the charging phenomenon. Degradation of the single electron transfer was observed with small counter-ions, which can penetrate into the monolayer and increase its capacitance. In another study, ion rectified MPC film charging response was shown to be due to ion solvation phenomena and could be treated analogously to a liquid|liquid interface, with charging onset potential dependent on the standard ion transfer potential of the counter-ion across the film|solution interface.

Aqueous stability of charged MPCs was also considered in the thesis. The solubility was demonstrated to be practically independent of the ionic strength of the solution for salts comprised of large counter-ions. These ions were shown to form an electrostatically bound steric barrier around the nanoparticle. Such solubility issues are very relevant for biosensor applications where typically aqueous dispersion of nanoparticles are used.

Dithiol place exchange of the MPC bound thiol is an interesting reaction and often used in the formation of MPC superstructures. Here, aggregation induced by interlinking MPCs with hexanedithiol was studied by dynamic light scattering and fitted to a simple kinetic model. This provided an indirect means to link the ligand exchange to the aggregation kinetics.

Finally, an application of gold nanoparticles to drug delivery is presented. Liposomes loaded with Au-MPCs and marker molecules were shown to be relatively stable and released their contents with an external signal i.e. laser irradiation. The technique would be an excellent option for drug delivery in particular in ocular medicine.

This thesis consists of an overview and of the following 6 publications:

  1. Bernadette M. Quinn, Peter Liljeroth, Virginia Ruiz, Timo Laaksonen and Kyösti Kontturi, Electrochemical Resolution of 15 Oxidation States for Monolayer Protected Gold Nanoparticles, Journal of the American Chemical Society, 2003, 125, 6644-6645.
  2. Päivi Ahonen, Timo Laaksonen, Antti Nykänen, Janne Ruokolainen and Kyösti Kontturi, Formation of Stable Ag-Nanoparticle Aggregates Induced by Dithiol Cross-Linking, Journal of Physical Chemistry B, 2006, 110, 12954-12958.
  3. Timo Laaksonen, Päivi Ahonen, Christoffer Johans and Kyösti Kontturi, Stability and Electrostatics of Mercaptoundecanoic Acid-Capped Gold Nanoparticles with Varying Counterion Size, ChemPhysChem, 2006, 7, 2143-2149.
  4. Timo Laaksonen, Outi Pelliniemi and Bernadette M. Quinn, Ion Permeability of SAMs on Nanoparticle Surfaces, Journal of the American Chemical Society, 2006, 128, 14341-14346.
  5. Timo Laaksonen, Virginia Ruiz, Lasse Murtomäki and Bernadette M. Quinn, Nanoparticle Film Charging – Ion Rectified or Ion Limited?, Journal of the American Chemical Society, 2007, 129, 7732-7733.
  6. Lauri Paasonen, Timo Laaksonen, Christoffer Johans, Marjo Yliperttula, Kyösti Kontturi and Arto Urtti, Gold Nanoparticles Enable Selective Light-Induced Contents Release from Liposomes, Journal of Controlled Release, accepted for publication.

Keywords: nanoparticles, electrochemistry, self-assembled monolayers, liposomes, ligand exchange

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© 2007 Helsinki University of Technology

Last update 2011-05-26