Mykola Borzenkov

Thermal and Chemical Stability of Thiol Bonding on Gold Nanostars.

The stability of thiol bonding on the surface of star-shaped gold nanoparticles was studied as a function of temperature in water and in a set of biologically relevant conditions. The stability was evaluated by monitoring the release of a model fluorescent dye, Bodipy-thiol (BDP-SH), from gold nanostars (GNSs) cocoated with poly(ethylene glycol) thiol (PEG-SH). The increase in the BDP-SH fluorescence emission, quenched when bound to the GNSs, was exploited to this purpose. A maximum 15% dye release in aqueous solution was found when the bulk temperature of gold nanostars solutions was increased to T = 42 °C, the maximum physiological temperature. This fraction reduces 3-5% for temperatures lower than 40 °C. Similar results were found when the temperature increase was obtained by laser excitation of the near-infrared (NIR) localized surface plasmon resonance of the GNSs, which are photothermally responsive. Besides the direct impact of temperature, an increased BDP-SH release was observed upon changing the chemical composition of the solvent from pure water to phosphate-buffered saline and culture media solutions. Moreover, also a significant fraction of PEG-SH was released from the GNS surface due to the increase in temperature. We monitored it with a different approach, that is, by using a coating of α-mercapto-ω-amino PEG labeled with tetramethylrhodamine isothiocyanate on the amino group, that after heating was separated from GNS by ultracentrifugation and the released PEG was determined by spectrofluorimetric techniques on the supernatant solution. These results suggest some specific limitations in the use of the gold-thiolate bond for coating of nanomaterials with organic compounds in biological environments. These limitations come from the duration and the intensity of the thermal treatment and from the medium composition and could also be exploited in biological media to modulate the in vivo release of drugs.

Fabrication of Inkjet-Printed Gold Nanostar Patterns with Photothermal Properties on Paper Substrate

Inkjet printing technology has brought significant advances in patterning various functional materials that can meet important challenges in personalized medical treatments. Indeed, patterning of photothermal active anisotropic gold nanoparticles is particularly promising for the development of low-cost tools for localized photothermal therapy. In the present work, stable inks containing PEGylated gold nanostars (GNSs) were prepared and inkjet printed on a pigment-coated paper substrate. A significant photothermal effect (ΔT ≅ 20 °C) of the printed patterns was observed under near infrared (NIR) excitation of the localized surface plasmon resonance (LSPR) of the GNS with low laser intensity (I ≅ 0.2 W/cm(2)). Besides the pronounced photothermal effect, we also demonstrated, as an additional valuable effect, the release of a model fluorescent thiol-terminated Bodipy dye (BDP-SH) from the printed gold surface, both under bulk heating and NIR irradiation. These preliminary results suggest the way of the development of a new class of low-cost, disposable, and smart devices for localized thermal treatments combined with temperature-triggered drug release.

Physical Properties of Gold Nanostars

The most relevant applications of gold nanostars are based on their physical properties. These arise primarily from resonant oscillations of the conduction electrons of the nanoparticles called localized surface plasmon resonances (LSPR). In this chapter an introduction to the physical origin of the LSPR and the way the nano-environment affect them are provided. Finally the implication of the LSPR of gold nanostar surface-enhanced Raman scattering is also discussed.

Self-assembled monolayers of Prussian blue nanoparticles with photothermal effect

Abstract A photo-responsive antibacterial surface was prepared grafting non-toxic Prussian blue nanoparticles on a functionalized glass surface. Colloidal Prussian blue was synthesized as nanoparticles with cubic shape and grafted on a polyamine-functionalized SiO2 surface, obtaining a good coverage and a homogeneous distribution of the nanocubes. Irradiation of these samples in the so-called ‘bio-transparent window’ of the near-infrared allows to exert a triggered antibacterial effect.

Gold Nanoparticles for Tissue Engineering

Regenerative medicine is currently recognized as an emerging field of nano-medicine with promising opportunities to fully heal tissues damaged by disease, trauma or congenital issues. Within this field, tissue engineering aims at the combination of cells, new bio-materials, and biochemical factors to regenerate biological tissues. The societal impact of this research is significant due to the possibility of implanting natural, synthetic, or semi-synthetic tissues and organs that are fully functional from the start, or can grow into the required functionality. Recently advances of nanotechnology provided wide possibilities to fabricate nanostructured scaffolds that mimic the tissue-specific microenvironment. The unique properties of a variety of nanomaterials allow to prepare scaffolds with improved biochemical, mechanical, and electrical properties and capable also to cell adhesion, proliferation, differentiation and to foster the cell growth. Within many types of nanoparticles, gold nanoparticles nowadays are widely used in biology and medicine due to the wide range of valuable chemical and physical properties. However, efficient application of gold nanoparticles for tissue engineering purposes is still at incipience stage.

Fabrication of photothermally active poly(vinyl alcohol) films with gold nanostars for antibacterial applications

The unique photothermal properties of non-spherical gold nanoparticles under near-infrared (NIR) irradiation find broad application in nanotechnology and nanomedicine. The combination of their plasmonic features with widely used biocompatible poly(vinyl alcohol) (PVA) films can lead to novel hybrid polymeric materials with tunable photothermal properties and a wide range of applications. In this study, thin PVA films containing highly photothermally efficient gold nanostars (GNSs) were fabricated and their properties were studied. The resulting films displayed good mechanical properties and a pronounced photothermal effect under NIR irradiation. The local photothermal effect triggered by NIR irradiation of the PVA-GNS films is highly efficient at killing bacteria, therefore providing an opportunity to develop new types of protective antibacterial films and coatings.

Photothermal effect of gold nanostars inkjet-printed on coated paper substrate under near-infrared irradiation

The research and development of personalized medical treatments is increasing steadily fostered by its large societal impact. The ability of non-spherical gold nanoparticles to locally and efficiently release heat when irradiated in Near Infrared (NIR) wavelength region is a promising tool for photothermal medical therapies. In the present work, stable inks containing PEGylated gold nanostars (GNS) were obtained and inkjet-printed on a pigment coated paper substrate. Significant photothermal effect of the printed patterns was observed under Near Infrared (NIR) excitation of the Localized Surface Plasmon Resonance (LSPR) of the GNS. These preliminary results support, in perspective, the application of printed GNS patterns for thermal medical treatments either by direct localized heating, or by temperature triggered drug release.

Photothermal effect of gold nanostar patterns inkjet-printed on coated paper substrates with different permeability

Summary Inkjet printing of spherical gold nanoparticles is widely applied in the fabrication of analytical and diagnostics tools. These methods could be extended to non-spherical gold nanoparticles that can efficiently release heat locally when irradiated in the near infrared (NIR) wavelength region, due to localized surface plasmon resonance (LSPR). However, this promising application requires the ability to maintain high efficiency and tunability of the NIR LSPR of the printed nanoparticles. In this study stable inks containing PEGylated gold nanostars (GNS) were fabricated and successfully inkjet-printed onto differently coated paper substrates with different porosity and permeability. A pronounced photothermal effect was observed under NIR excitation of LSPR of the printed GNS patterns even at low laser intensities. It was found that beside the direct role of the laser intensity, this effect depends appreciably on the printing parameters, such as drop density (δ, drops/mm2) and number of printed layers, and, critically, on the permeability of the coated paper substrates. These results will promote the development of GNS-based printed platforms for local photothermal therapy.

Interactions of Gold Nanostars with Cells

Unique optical properties, chemical stability, ease of synthesis, and wide functionalization possibilities make GNP attractive candidates for use in biomedical research including chemical sensing, biological imaging, drug delivery, and cancer treatment. In particular, the strong two-photon luminescence of GNP coupled to a specific targeting makes them ideal candidates as contrast agents. To this aim, the interaction with cells and their cellular tracking are important issues for successful application of GNP to biomedical purposes. Properties of gold nanoparticles, namely gold nanostars, as contrast agents and interaction of GNS with cells are highlighted in this chapter.

Gold Nanostar Synthesis and Functionalization with Organic Molecules

This chapter is devoted to the synthesis and functionalization of gold nanostars. The physical-chemical characterization and singular features of gold nanostars with respect to other types of gold nanoparticles are provided. Various methods of GNS synthesis as well as of the functionalization of GNS with PEG, organic dyes, and bioactive compounds are discussed.