Laser ablation synthesis of noble metal and metal oxide nanoparticles for sensing and drug delivery applications

After more than 20 years of basic nanoscience research and more than fifteen years of focused development, the entire society can benefit of both expected and unexpected applications of nanotechnology. In particular, the use of nanoparticles are considerably improving many technologies and industrial sectors: information technology, homeland security, medicine, transportation, energy, environmental science, and many others. The properties of many conventional materials change when made up of nanoparticles. This is typical, because nanoparticles have a greater surface area per weight than larger particles which causes them to be more reactive to other molecules. Many benefits of nanoparticles depend on the possibility to tailor the surface/volume ratio which allows to achieve specific properties. In fact, materials can effectively be made stronger, lighter, more durable, more reactive, or better electrical conductors. Many everyday commercial products currently on the market rely on nanoscale materials and processes, such as: The use of polymeric micelle nanoparticles to deliver drugs to tumors; The use of polymer coated iron oxide nanoparticles to break up clusters of bacteria, possibly allowing more effective treatment of chronic bacterial infections; Metal oxide nanoparticles act as an antioxidant to remove oxygen free radicals that are present in a patient’s bloodstream following a traumatic injury. The nanoparticles absorb the oxygen free radicals and then release the oxygen in a less dangerous state, freeing up the nanoparticle to absorb more free radicals;Iron nanoparticles are being used to clean up carbon tetrachloride pollution in ground water; Noble metal nanoparticles such as silver (Ag) and gold (Au) have unique plasmonic properties that give rise to surface enhanced Raman scattering (SERS). SERS enhancement depends on the chemical composition and structure of these nanoparticles. Research activities are focused in optimizing the design of Ag/Au hybrid nanoparticles for SERS-based detection methods. Recent years have witnessed great interest in the development of SERS nanoprobes for Raman imaging. Rationally designed SERS nanoprobes have greatly enhanced Raman signals by several orders of magnitude, thus showing great potential for biosensing applications; Nanoparticles can be incorporated into solar panels to convert sunlight to electricity more efficiently, promising inexpensive solar power in the future. Nanostructured solar cells could be cheaper to manufacture and easier to install, since they can use print-like manufacturing processes and can be made in flexible rolls rather than discrete panels. Newer research suggests that future solar converters might even be "paintable". To open up new opportunities for producing high-performance nanomaterials, useful for different technological applications, the outcomes of this PhD thesis are: 1. defining strategies to force pulsed laser ablation method (mainly in a liquid environment) to grow metal based nanoparticles with fine control on compositional and morphological properties, appropriate for a specific surface functionalization; 2. providing a systematic study of the mechanisms involved during the ablation process such as the cavitation bubbles formation and their effects on nanoparticles properties; in particular it was evaluated the impact on the nanoparticles size of cavitation bubbles shape and of dynamics changes due to the re-irradiation of the target; 3. demonstrating the transversal empowering of the synthesized material through its application for: SERS activity of Au nanoparticles produced by picosecond ablation to obtain the first SERS spectrum of the new generation antiepileptic drug perampanel, whose clinical interest is relevant. A controlled synthesis of Au nanoparticles by both nanosecond and picosecond pulsed laser ablation in water (PLAL), with no stabilizing agent, was carried out obtaining a narrow size distribution and a remarkable long-term stability. Then, Au nanoparticles efficiency was tested by collecting the first FT-Raman and SERS spectra of perampanel; a controlled drug release at a specific target site in response to external stimuli (laser light sources and magnetic field). Specifically, the synthesis and characterization of a new type of external- activated drug delivery carrier made of silver, gold and iron oxide nanoparticles embedded in PEG-PLA or PEG-PLGA polymeric nanoplatforms were carried out. These systems allow to encapsulate (89%) and to release with a high efficiency (about 10%) of silibilin, working as drug delivery triggered by external stimuli, applicable to the biomedical field; a new generation of a resistive hydrogen sensor based on rhodium oxide nanoparticles which shows high response to low concentration of the target gas in air and at low operating temperature. It has been developed a simple approach providing a general way to prepare new hydrogen sensing materials based on colloidal rhodium oxides nanoparticles while eliminating the nanofabrication obstacles of previous ones. We also demonstrated, for the first time, the sensing properties of these nanostructures toward low concentration of hydrogen in air, fabricating a simple and promising conductometric platform for novel H2 sensors that can be applied for environmental monitoring, biomedical as well as industrial safety applications. The thesis is organized in five chapters. Chapter 1 is a short overview on the basic nanoparticles properties and on the synthesis approach. Chapter 2 is focussed on the Pulsed Laser Ablation synthesis process carried out in a liquid environment. In this chapter a brief overview of some phenomena involved during the ablation process is reported. In Chapter 3 are described some results on cavitation bubbles and the influence of the re-irradiation of the target on bubble shape and dynamics. Moreover, the impact on nanoparticles properties has been evaluated. These results were acquired during my internship in the laboratory of Technical Chemistry in Essen. Chapter 4 deals on the synthesis and characterization of plasmonic nanoparticles: Silver, Gold, and Rhodium. In this chapter is reported initially a study on ablation parameters tuning, in order to optimize NPs size distribution in view of SERS sensing applications. In chapter 5 is reported about the synthesis and characterization of plasmonic noble metal nanoparticles for drug delivery. Finally, chapter 6 deals on the synthesis of Rhodium-Rhodium oxide nanoparticles for hydrogen gas sensor devices.