Preparation and characterization of metallic and metal oxide nanoparticles for biomedical applications

Two of the 21st century most promising technologies are biotechnology and nanotechnology. This science of nanoscale structures deals with the creation, investigation and utilization of systems that are 1000 times smaller than the components currently used in the field of microelectronics. Convergence of these two technologies results in growth of nanobiotechnology. This interdisciplinary combination can create many innovative tools. The biomedical applications of nanotechnology are the direct products of such convergence. Indeed, due to their unique size-dependent properties, nanomaterials have the potential to revolutionize the detection, diagnosis, and treatment of diseases by offering superior capabilities compared to conventionally used materials. Today nanomaterials have been designed for a variety of biomedical and biotechnological applications, including biosensors, enzyme encapsulation; neuronal nanotechnology, on the other hand, is based on the introduction of novel nanomaterials which can result in revolutionary new structures and devices using extremely biologically sophisticated tools to precisely position molecules. Nanotechnology in biomedical sciences presents many revolutionary opportunities in the fight against all kinds of cancer, cardiac and neurodegenerative disorders, infection and other diseases. Utility of nanotechnology to biomedical sciences imply creation of materials and devices designed to interact with the body at sub-cellular scales with a high degree of specificity. This could be potentially translated into targeted cellular and tissue-specific clinical applications aimed at maximal therapeutic effects with very limited adverse-effects. Nanoparticles are part of the family of devices nanotechnology had given birth to. By their size and morphologic properties they encounter a large panel of different applications, biomedical applications are part of this panel. These specific nanoparticles can cover different functions from diagnosis to direct treatment; more specifically they can be used as carriers for specific delivery of drugs or as vector for specific therapies. In a first chapter different kind ofnanoparticles will be described in a first time, and the related therapy they apply to will be explained in a second time. In order to be used for this specific kind of application, the nanoparticles should comply with a certain number of requirements and specifications. To this end, not only the materials used for their preparation, but also the method employed should satisfy such requirements. In a second chapter, the requirements will be listed and their implications will be explained, and in the third chapter specific preparation methods meeting these criteria will be described. A lot of research is currently being conducted on this specific topic, for this reason it is a challenge to constantly find new methods of preparation and new materials meeting all the previously described requirements and in the same time bringing and improvement in the potential treatments. In the fourth chapter will be described the materials and methods I used to prepare devices and take up that challenge. Firstly, a new fast and convenient method is reported for preparing magnetic nanoparticles with a Fe3O4 core and a Poly(ethylene glycol)-diacrylate shell in water. A reduction coprecipitation method was used to obtain Fe3O4 in aqueous solution whereas the PEGDA coating was obtain via photochemical reaction at room temperature in an initiator free aqueous system. The fact that this method is solvent free and initiator free makes it ideal for biomedical applications. Secondly, magnetite nanoparticles were coated following a previous surface functionalization. The Fe3O4 nanoparticles were obtained as before and further stabilized with citric acid. Afterwards nanoparticles surface was modified by a silanization reaction with vinyltrimethoxysilane involving magnetite hydroxyl groups. Vinyl functionalized nanoparticles were coated with poly (ethylene-glycol) (PEG) using PEG dithiol (PEG-SH) under UV irradiation. Thiol-ene is a free-radical reaction that proceeds by a step-growth mechanism, involving two main steps, a free-radical addition followed by a chain transfer reaction; this reaction is well known for occurring in absence of any radical photoinitiator making it ideal for eventual biomedical applications. Thirdly, the use of ―click‖ reactions for preparing magnetic NPs with Fe3O4core and different biocompatible polymeric shells is reported. Magnetite nanoparticles were obtained following the same procedure that in the first two studies. As a next step, magnetic nanoparticles surface was modified by a silanization reaction with (3-bromopropyl)trimethoxysilane in order to introduce bromine groups on the particles surface. Afterwards the bromine groups were converted to azide groups by the reaction with sodium azide in order to obtain azide groups to take part to click reaction with alkyne functionalized polymers. For this reason, acetylene functionalized poly(ethylene glycol) (a-PEG) and poly(ε-caprolactone) (a-PCL) were synthesized and grafted onto the surface of azide functionalized nanoparticles via ―click‖ reaction to obtain monodisperse magnetic nanoparticles. The peculiar characteristics of this method make it ideal for biomedical applications. Fourthly, a new, fast and convenient method for preparing gold nanoparticles with a poly(ethylene glycol)-diacrylate (PEGDA) shell in water is reported. Polyethyleneglycol (PEG) was used as hydrophilic monomer in emulsifier-free emulsion polymerization to form polymeric nanoparticles by the UV-induced process. At the same time, gold was generated as the core of the PEG nanospheres by the reduction of HAuCl4 activated through the radical photogenerated from 2-hydroxy-2-methyl-1-phenyl-1-propanone. This one-step procedure is very easy to implement and fast. Moreover, the fact that this method is performed in water makes it ideal for biomedical applications. Fifthly, hollow gold nanoparticles were prepared and coated with Poly(ethylene glycol) methyl ether thiol. In a first time, cobalt nanoparticles were prepared by reduction of cobalt salts and in a second time gold salts were reduced on the surface of cobalt nanoparticles forming a gold shell while consuming the cobalt, leaving at the end of the reaction a hollow gold nanoparticles. Successively these devices were coated with the polymer taking advantage of the natural affinity between thiol groups and gold. Sixthly, gold nanoshell were prepared and coated with Poly(ethylene glycol) methyl ether thiol. Gold nanoshells are constituted by a silica core and a gold shell. Silica nanoparticles were obtained by the well-known Stöber method, then gold seeds (3 nm diameter) were grafted on the surface of these silica nanoparticles and successively grown by gold salts addition until obtaining a continuous and homogeneous gold shell. In the end these devices were coated with the polymer taking advantage of the natural affinity between thiol groups and gold. The fifth and sixth chapters describe the characterization of these devices correlated to their potential applications.