In the thesis, the results obtained during my 3-years PhD activity in the two major research fields of renewable energy and organic bioelectronics are reported. In particular, two main topics are treated, such as 1. Organic semiconductor-based, photocatalytic water splitting and 2. Organic prosthetic devices for sight restoring. In the first part of the thesis, organic semiconductors are generally described from the point of view of their peculiar optical and electronic characteristics. Their capability of charge generation and transport upon illumination renders them particularly appealing for the development of any kind of application requiring a photovoltaic, low-voltage operating regime. For our projects, particular interest is elicited by polymers showing active functionality in the range of visible light. Besides photovoltaic cells applications they can, in fact, be originally employed in different fields currently mainly dominated by inorganic materials, such as water splitting and prosthetic devices realization. Biocompatibility and biostability properties of organic materials are moreover taken into account, providing an accurate view of the related current knowledge at the state of the art. Biocompatibility, in particular, is a peculiar characteristic of most organics; it descends from their carbon-based backbone rendering them similar to tissues´ structure and thus suitable for bio-mimetic applications and prosthetic purposes. After the introductory part, the first research topic treated, i.e. water splitting, is reviewed in detail. The water splitting phenomena is presented from both the theoretical and the devices` point of view. In reviewing the many different water splitting systems reported in literature at the best of our knowledge, most of which employing inorganic semiconductors such as titanium dioxide as active materials and operating upon external bias application, particular attention is devoted in the description of such systems which alternatively operate under photovoltaic conditions and/or employ organic materials as active layers. Consequently, the thin film, polymer-based, photocatalytic water splitting devices developed in our laboratories are presented. The description of such devices from both the realization and characterization point of view is organized as listed in the following: 1. Description of materials´ processing techniques for devices` realization, 2. Description of optical, electrical and electrochemical techniques and relative set up employed for devices` testing, 3. Presentation and interpretation of collected experimental data, with particular focus on the characterization of photogenerated chemical reactions taking place at the polymer/water interface. In particular, the innovative possibility to promote gaseous hydrogen from bulk water using a simple polymeric thin film as a photocatalyst under photovoltaic conditions (with no additional bias applied) upon visible light illumination is presented, 4. Characterization of the polymer/aqueous solution interface and development of a possible interpretation model, able to describe the charges exchange mechanisms at the polymer/water interface, not yet formalized in literature. Possible future developments of the devices` are moreover presented, with particular focus on the solar-to-hydrogen efficiency maximization. In the second part of the work, the field of organic bioelectronics is taken into account. A detailed review of literature regarding this field is provided, with particular attention to the areas of prosthetic devices and transistors for sensing. Our project´s aim concerns the realization of an all-organic, prosthetic device, totally operating under photovoltaic conditions, able to substitute a damaged human retina, subject of particular degenerative diseases which destroy the retinal photoreceptors, such as retinite pigmentosa. The organic artificial retina is conceived as a matrix of pixels, i.e. organic photodiodes, which act as photoreceptors and transduce optical signals into electrical ones. Two main results have been obtained until now within this project and are described in the thesis. The first one concerns the communication between a polymer-based organic device and rats´ hippocampal primary neurons. We in fact demonstrated for the first time how it is possible to obtain neurons´ stimulation using only visible light as an input and a simple polymeric thin film as a mediating platform. This result not only constitutes a fundamental and necessary step for the future realization of the prosthetic implant, but also establishes a new communication protocol between neuronal cells and prosthetic devices. The second fundamental result of our research concerns the stimulation of ganglion cells of blind rats´ explanted retinas. When retinal photoreceptors cells are damaged by certain diseases, blindness is caused in the patient. However, if all other retinal cellular layers are preserved, it is still possible to obtain photostimulated signals to be delivered to the optical nerve, able in principle to restore sight. A very simply structured, polymer-based, thin film device is thus demonstrated to be able to elicit stimulation of retinal ganglion cells (which are responsible for signals delivery to the optical nerve) in rats´ explanted blind retinas. Stimulation has been tested under visible light illumination for different light pulses even within the day-light limit. As a further development within the retina prosthesis project, results of our research for biomimetic and biocompatible materials to be used as scaffolds for polymeric thin film based devices in in-vivo implants are reported. As a conclusion, future perspectives for polymer-based retinal prosthesis are taken into consideration, focusing on the most relevant issues to be faced, such as biocompatibility and biostability over time. Necessary further improvements for the devices are also underlined, such as, for example, the necessity to realize a proper organic pixels matrix within the polymeric active device, in order to mimic the natural photoreceptor distribution in the retina.
La tesi riepiloga i risultati ottenuti nel corso del dottorato nell'ambito di due argomenti: 1. Water splitting con semiconduttori organici; 2. Bioelettronica organica. Dopo un riepilogo delle caratteristiche principali dei semiconduttori organici, con particolare riferimento alle loro proprietà opto-elettroniche e di biocompatibilità, viene proposta una panoramica sul Water Splitting (WS), sia dal punto di vista teorico che dei dispositivi esistenti allo stato dell'arte. Si pone particolare attenzione alla classe dei dispositivi organici per WS, nostro oggetto di studio. Vengono poi presentati i dispositivi ibridi solido/liquido per WS basati su film sottili polimerici, sviluppati presso i nostri laboratori. Gli argomenti trattati sono: 1. Tecniche di realizzazione dei dispositivi; 2. Tecniche di caratterizzazione ottica, elettronica ed elettrochimica e descrizione dei set-up utilizzati; 3. Presentazione ed interpretazione dei dati sperimentali raccolti, con focus sulle reazioni chimiche fotogenerate sotto luce visibile all’interfaccia polimero/acqua e particolare attenzione alla generazione di idrogeno gassoso dall’acqua; 4. Caratterizzazione dell’interfaccia polimero/soluzione acquosa e possibile modello per il meccanismo di scambio di carica all’interfaccia polimero/acqua, non precedentemente formalizzato in letteratura. Successivamente viene proposta una panoramica dei dispositivi esistenti nel campo della bioelettronica organica, con particolare attenzione all'ambito delle protesi visive e dei transistors per rilevazione. Nell'ambito del nostro progetto per la realizzazione di una protesi retinica polimerica operante in regime fotovoltaico, si dimostra come sia stato possibile ottenere, per la prima volta, fotostimolazione in luce visibile di neuroni primari ippocampali e di retine cieche espiantate, utilizzando film sottili di diversi materiali attivi polimerici. Si descrivono poi gli stadi di realizzazione del successivo dispositivo per impianto su animali vivi, in particolare: la scelta di un adeguato supporto a base organica, dei materiali polimerici utilizzati come elettrodi o per fotogenerazione di carica e lo studio della biocompatibilità del dispositivo. Si propone un modello di funzionamento per l’interfaccia polimero/neuroni o retina. Si riportano infine i principali risultati ottenuti nella realizzazione e caratterizzazione di transistors organici elettrochimici o a film sottile in grado di lavorare in ambienti acquosi con finalità di rilevazione di strati o attività cellulare. Vengono infine proposte le le possibili prospettive di sviluppo dei progetti presentati.
Solid/liquid organic devices for energy and life science
LANZARINI, ERICA
Abstract
In the thesis, the results obtained during my 3-years PhD activity in the two major research fields of renewable energy and organic bioelectronics are reported. In particular, two main topics are treated, such as 1. Organic semiconductor-based, photocatalytic water splitting and 2. Organic prosthetic devices for sight restoring. In the first part of the thesis, organic semiconductors are generally described from the point of view of their peculiar optical and electronic characteristics. Their capability of charge generation and transport upon illumination renders them particularly appealing for the development of any kind of application requiring a photovoltaic, low-voltage operating regime. For our projects, particular interest is elicited by polymers showing active functionality in the range of visible light. Besides photovoltaic cells applications they can, in fact, be originally employed in different fields currently mainly dominated by inorganic materials, such as water splitting and prosthetic devices realization. Biocompatibility and biostability properties of organic materials are moreover taken into account, providing an accurate view of the related current knowledge at the state of the art. Biocompatibility, in particular, is a peculiar characteristic of most organics; it descends from their carbon-based backbone rendering them similar to tissues´ structure and thus suitable for bio-mimetic applications and prosthetic purposes. After the introductory part, the first research topic treated, i.e. water splitting, is reviewed in detail. The water splitting phenomena is presented from both the theoretical and the devices` point of view. In reviewing the many different water splitting systems reported in literature at the best of our knowledge, most of which employing inorganic semiconductors such as titanium dioxide as active materials and operating upon external bias application, particular attention is devoted in the description of such systems which alternatively operate under photovoltaic conditions and/or employ organic materials as active layers. Consequently, the thin film, polymer-based, photocatalytic water splitting devices developed in our laboratories are presented. The description of such devices from both the realization and characterization point of view is organized as listed in the following: 1. Description of materials´ processing techniques for devices` realization, 2. Description of optical, electrical and electrochemical techniques and relative set up employed for devices` testing, 3. Presentation and interpretation of collected experimental data, with particular focus on the characterization of photogenerated chemical reactions taking place at the polymer/water interface. In particular, the innovative possibility to promote gaseous hydrogen from bulk water using a simple polymeric thin film as a photocatalyst under photovoltaic conditions (with no additional bias applied) upon visible light illumination is presented, 4. Characterization of the polymer/aqueous solution interface and development of a possible interpretation model, able to describe the charges exchange mechanisms at the polymer/water interface, not yet formalized in literature. Possible future developments of the devices` are moreover presented, with particular focus on the solar-to-hydrogen efficiency maximization. In the second part of the work, the field of organic bioelectronics is taken into account. A detailed review of literature regarding this field is provided, with particular attention to the areas of prosthetic devices and transistors for sensing. Our project´s aim concerns the realization of an all-organic, prosthetic device, totally operating under photovoltaic conditions, able to substitute a damaged human retina, subject of particular degenerative diseases which destroy the retinal photoreceptors, such as retinite pigmentosa. The organic artificial retina is conceived as a matrix of pixels, i.e. organic photodiodes, which act as photoreceptors and transduce optical signals into electrical ones. Two main results have been obtained until now within this project and are described in the thesis. The first one concerns the communication between a polymer-based organic device and rats´ hippocampal primary neurons. We in fact demonstrated for the first time how it is possible to obtain neurons´ stimulation using only visible light as an input and a simple polymeric thin film as a mediating platform. This result not only constitutes a fundamental and necessary step for the future realization of the prosthetic implant, but also establishes a new communication protocol between neuronal cells and prosthetic devices. The second fundamental result of our research concerns the stimulation of ganglion cells of blind rats´ explanted retinas. When retinal photoreceptors cells are damaged by certain diseases, blindness is caused in the patient. However, if all other retinal cellular layers are preserved, it is still possible to obtain photostimulated signals to be delivered to the optical nerve, able in principle to restore sight. A very simply structured, polymer-based, thin film device is thus demonstrated to be able to elicit stimulation of retinal ganglion cells (which are responsible for signals delivery to the optical nerve) in rats´ explanted blind retinas. Stimulation has been tested under visible light illumination for different light pulses even within the day-light limit. As a further development within the retina prosthesis project, results of our research for biomimetic and biocompatible materials to be used as scaffolds for polymeric thin film based devices in in-vivo implants are reported. As a conclusion, future perspectives for polymer-based retinal prosthesis are taken into consideration, focusing on the most relevant issues to be faced, such as biocompatibility and biostability over time. Necessary further improvements for the devices are also underlined, such as, for example, the necessity to realize a proper organic pixels matrix within the polymeric active device, in order to mimic the natural photoreceptor distribution in the retina.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/74363