Miranda, Bruno (2023) Multifunctional Hybrid Nanoresonators for Biosensing Applications: Design, Fabrication, and Characterization. [Tesi di dottorato]

Anteprima

Testo Miranda_Bruno_XXXV.pdf Download (51MB) | Anteprima

Abstract

Nanophotonics, bridging together nanoscience and photonics, is becoming a key enabling technology in biomedicine showing great promises in early diagnosis and less-invasive therapies. In this context, the unique features of plasmonic and dielectric nanoresonators to localize and/or enhance light at the nanoscale are greatly contributing to biosensing and enhanced spectroscopies. Properly engineered metallic and dielectric nanoresonators, exhibiting tunable resonant behavior, can provide an unprecedented level of control over the light in subwavelength spatial regions. The resonances of these objects strongly depend on their size, shape, composition, and surrounding media. Therefore, their effective electromagnetic modeling and its continuous cross-talk with experimental observations represent the best way to meet the demand for standardized, easy-to-use, large-scale, and low-cost optical devices for biomedical applications. From the theoretical perspective, the growing efforts of scientists to provide a complete framework for the description of both metallic and dielectric nanostructures has resulted in powerful tools, in particular spectral theories, in which the resonant object is described by means of all its resonant modes. From the experimental perspective, instead, scientific and technological advances are operating a deep translation of the typical industrial microfabrication approaches to the nanoscale to meet the demand for metallic and dielectric nanostructured devices to be operated in all the fields of science, including biomedicine. Both top-down (from bulk materials to nanomaterials) and bottom-up (from the molecular scale to nanoscale) approaches have been proposed for the fabrication of plasmonic and all-dielectric nanoresonators, which have been largely applied in biomedicine for biosensing applications. However, finding an optimal trade-off between performance and fabrication cost still represents the bottleneck of their employment in everyday life. The pandemic outbreak of Covid-19 has in fact highlighted the necessity of rapid, simple-to-use, affordable, and accurate biosensing platforms for the screening of the population on a large scale. Such devices do not need expensive and time-consuming analytical techniques that require experienced staff and long waiting times. In this context, a winning strategy for the design and application of optical nanoresonators in biomedicine could be exploiting the continuous interplay between theoretical predictions and experimental observations. This approach could enable the achievement of fully-predictable systems that can be fabricated on a large scale, with good reproducibility and satisfactory performance. Motivated by this necessity, in this thesis, a novel paradigm in the design of multifunctional hybrid nanoresonators is proposed and experimentally validated. This paradigm could lead to the fabrication and characterization of novel nanosystems, which could find large applications in biosensing. In Chapter 1, the recent highlights in the applications of metallic and dielectric nanoresonators in biomedicine and their fabrication approaches are reviewed. Moreover, due to the more standardized bottom-up approaches for their synthesis, plasmon-based optical biosensors are thoroughly described, in which hybrid nanoparticles with multiple functionalities are introduced as optical transducers. In Chapter 2, the theoretical background of the electromagnetic scattering of optically small objects is carefully reviewed, with particular emphasis on the Mie Theory. Moreover, a spectral scattering theory is introduced and applied to the most important building blocks of plasmonic and dielectric nanoresonators, mainly constituted by spherical nanoparticles and thin nanowires, respectively. The spectral theory enables the understanding of the scattering of these homogeneous nanostructures in the framework of the electroquasistatic and magnetoquasistatic approximations of the Maxwell equations, guaranteeing the good prediction of the resonance position and quality factor of their modes. In Chapter 3, the concept of hybrid nanoparticles is introduced. The Maxwell Garnett homogenization theory is introduced briefly. This theory describes the effective dielectric permittivity of a composite medium with inclusions. The composition of these hybrid systems is found by means of a reverse engineering approach based on the genetic optimization, the Maxwell Garnett theory, and the Mie theory. Moreover, the Mie-Kerker theory is also used for the description of the electromagnetic scattering from coated hybrid nanoparticles. The validation of the obtained model is proposed starting from standard hybrid plasmonic nanoparticles synthesized \textit{via} bottom-up approaches. In Chapter 4, a novel hybrid drug delivery nanosystem is presented. It is based on porous biosilica nanoparticles and \textit{in-situ} synthesized gelatin/gold nanoparticles. The composition of the gelatin-stabilized plasmonic nanoparticles is found by genetic optimization. The obtained hybrid nanosystem is further coated with gelatin shells of increasing thicknesses. Then, a theoretical model is introduced that allows, from simple spectroscopic measurements, to determine the shell degradation and consequent drug release. The proposed nanosystem could represent a valid alternative for the\textit{in-vivo} monitoring of the drug release from a nanocarrier. In Chapter 5, novel hybrid nanocomposites based on polyethylene glycol diacrylate hydrogels and citrate-capped gold nanoparticles are proposed. The optimization of the fabrication technique takes advantage of the high reproducibility, large scalability, and simplicity of an all-solution fabrication strategy. The optical properties of the obtained nanocomposites can be easily predicted within the hybrid nanoparticles framework. The mechanical properties of hydrogels with different molecular weights result to have an effect on the optical features of the hybrid nanocomposites. These features are exploited to obtain devices with different transduction mechanisms. The obtained devices exhibit excellent performances in the selective and sensitive detection of a model target molecule. The presented devices direct find applications in wearable biosensors, and food and environmental monitoring. Moreover, they could be easily integrated within more complex microfluidic and microelectronic components due to the intrinsic flexible nature of the polymeric matrix in which the nanoparticles are embedded.

Downloads

Actions (login required)

Modifica documento