The research was focused on the development of marker-free optical sensors based on plastic optical fibers (POF). These are particularly suitable for sensing application because of their exceptional flexibility, large numerical aperture, and easy manipulation. Also, they are able to withstand smaller bend radii than glass fibers. Therefore, POFs are suitable for the realization of low-cost and miniaturized optical sensors both robust and highly sensitive for application with a remote control. Two approaches have been exploited the first in which the optical platform was directly developed on plastic optical fibers (POF) (intrinsic sensors) and the second that employ different waveguides made for example of PMMA or PET (extrinsic sensors). The two approaches show distinct characteristics of easy preparation and have been investigated to obtain a better reproducibility. In both sensors, different optical phenomena have been exploited, in particular, surface plasmon resonance (SPR) and the evanescent wave coupling (EWC). All the sensors employ synthetic biomimetic receptors, i.e. molecularly imprinted polymers (MIPs) for the detection of analytes in complex aqueous or organic matrices. The most commonly used bio-receptors, despite their high selectivity and sensitivity, suffer from great disadvantages as not being available for all the substrate, being limited to the biological condition of analysis and requiring an expensive and time-consuming development procedure. Instead, MIPs are more resistant, even in harsh conditions of analysis, while maintaining the high affinity and selectivity of the biological receptors, so making these synthetic receptors really promising for sensing purposes. Some specific MIPs have been developed, based on non-covalent interactions template-functional monomers, and with the most common composition as far as the functional monomer and the cross-linker are concerned. In some cases, the MIP composition was optimized by computational methods considering different functional monomers and cross-linkers as well as possible interfering interactions. The MIPs characteristics, as the affinity constant, the capacity of uptake and selectivity have been evaluated by batch procedure and the flow procedure. Porous MIP particles and MIP beads have been considered and characterized by batch equilibration. In particular MIPs for sensing the following molecules have been developed and characterized: 2-FAL (2-furhaldehide) and dibenzyldisulfide (DBDS) because of their rising importance as useful markers of health status of the middle tension transformers in the large distribution energy. 2-FAL was considered in aqueous matrices too, in view of its relevance in food quality control. The optical sensors developed have been characterized by determining the adsorption isotherms on the polymeric layer, based on the sensor response. The sensors based on SPR appear to be really promising due to the optimal sensitivity, low cost and possibility of miniaturization by employing POFs. Moreover, a high selectivity and affinity constant (Kaff), a low LOD and the possibility of the re-use are provided by the successful implementation of MIPs as receptors. Similar optimal results have been obtained by the evanescent wave coupling (EWC) moreover this platform presents the advantages of avoiding the use of Au layer, so could be superior to the SPR ones for the better reproducibility. Also, new kinds of molecularly imprinted materials have been considered in order to improve the biocompatibility of the sensing devices. In particular silk fibroin has been examined for its good optical and mechanical characteristics. Moreover, it is a biomaterial already approved for biomedical applications. Preliminary results on the imprinting of fibroin with glucose have been promising, with an imprinting factor higher than one. Moreover, the imprinted material can easily obtain a thin layer, which is particularly suitable for sensor development.
La ricerca è stata incentrata sullo sviluppo di sensori ottici (senza impiego di indicatori) basati su fibre ottiche plastiche (POF). Queste presentano caratteristiche vantaggiose come flessibilità, grande apertura numerica e facile lavorazione; essendo inoltre in grado di sopportare curvature più strette rispetto alle fibre di vetro. Pertanto, le POF risultano adatte alla realizzazione di sensori ottici ad alta sensibilità, miniaturizzati, robusti ed a basso costo. Due approcci differenti sono stati impiegati: il primo è stato basato sullo sviluppo dei sensori direttamente sulle fibre ottiche plastiche (POF) (sensori intrinseci) e il secondo prevede l'impiego di diverse guide d'onda ad esempio in PMMA o PET (sensori estrinseci). I due approcci mostrano caratteristiche distinte per la facile preparazione e sono stati studiati al fine di ottenere una migliore riproducibilità. I sensori sfruttano diversi fenomeni ottici: la risonanza plasmonica di superficie (SPR) o l'accoppiamento di onde evanescenti (EWC). Tutti i sensori impiegano recettori biomimetici sintetici, cioè polimeri a stampo molecolare (MIP) per il rilevamento di analiti in matrici complesse acquose o organiche. I bio-recettori comunemente usati, nonostante la loro elevata selettività e sensibilità, soffrono di grossi svantaggi quali la non disponibilità per tutti i substrati, il limite di analisi in condizioni biologiche e la costosa e lunga procedura per il loro utilizzo. Invece i MIP risultano più resistenti, anche in condizioni di analisi più drastiche (elevate T, bassi pH,…), pur mantenendo affinità e selettività elevate, pari a quelle dei bio-recettori. Tali caratteristiche rendendo questi recettori sintetici utili ai fini sensoristici. Sono stati sviluppati MIP specifici, basati su monomeri funzionali che impiegano interazioni non covalenti con comune composizione riguardo il monomero funzionale e il cross-linker. In alcuni casi, la composizione MIP è stata ottimizzata mediante metodi computazionali considerando diversi monomeri funzionali e cross-linker nonché possibili interazioni interferenti. Le caratteristiche dei MIP, come costante di affinità, capacità di assorbimento e selettività sono state valutate mediante procedura di equilibrazione batch e procedura a flusso. Differenti formulazioni di MIP in forma di particelle porose e sferiche sono state considerate. Sono stati sviluppati e caratterizzati MIP per l'analisi delle seguenti molecole: furaldeide (2-FAL) e dibenzildisolfuro (DBDS) data la loro importanza come utili indicatori dell'usura dei trasformatori di media tensione. La 2-FAL è stata considerata anche in matrici acquose, data la sua rilevanza nel controllo qualità degli alimenti. I sensori ottici sono stati caratterizzati determinando le isoterme di adsorbimento sullo strato polimerico, basato sulla risposta del sensore. I sensori SPR risultano promettenti grazie alla elevata sensibilità, al basso costo e alla possibilità di miniaturizzazione impiegando le POF. Inoltre, l'impiego di MIP come recettore garantiscono un'elevata selettività e costante di affinità (Kaff), un basso LOD e la possibilità del riutilizzo. Simili risultati sono stati ottenuti con sensori basati sull'accoppiamento di onde evanescenti (EWC) che tuttavia risultano più promettenti delle piattaforme SPR presentando il vantaggio dell'eliminazione dello strato di oro e quindi una migliore riproducibilità. Inoltre, nuovi materiali per l'imprinting molecolare sono stati considerati per migliorare la biocompatibilità. In particolare, la fibroina della seta è stata esaminata date le sue ottimali proprietà ottiche e meccaniche ed essendo un biomateriale già approvato per applicazioni biomediche. Risultati preliminari sull'imprinting di fibroina con glucosio sono stati promettenti; riscontrando un fattore di imprinting superiore a uno. Tale materiale stampato è facilmente ottenuto come strato sottile adatto allo sviluppo di sensori.
Optoelectronic sensors based on molecularly imprinted polymers
MARCHETTI, SIMONE
2019
Abstract
The research was focused on the development of marker-free optical sensors based on plastic optical fibers (POF). These are particularly suitable for sensing application because of their exceptional flexibility, large numerical aperture, and easy manipulation. Also, they are able to withstand smaller bend radii than glass fibers. Therefore, POFs are suitable for the realization of low-cost and miniaturized optical sensors both robust and highly sensitive for application with a remote control. Two approaches have been exploited the first in which the optical platform was directly developed on plastic optical fibers (POF) (intrinsic sensors) and the second that employ different waveguides made for example of PMMA or PET (extrinsic sensors). The two approaches show distinct characteristics of easy preparation and have been investigated to obtain a better reproducibility. In both sensors, different optical phenomena have been exploited, in particular, surface plasmon resonance (SPR) and the evanescent wave coupling (EWC). All the sensors employ synthetic biomimetic receptors, i.e. molecularly imprinted polymers (MIPs) for the detection of analytes in complex aqueous or organic matrices. The most commonly used bio-receptors, despite their high selectivity and sensitivity, suffer from great disadvantages as not being available for all the substrate, being limited to the biological condition of analysis and requiring an expensive and time-consuming development procedure. Instead, MIPs are more resistant, even in harsh conditions of analysis, while maintaining the high affinity and selectivity of the biological receptors, so making these synthetic receptors really promising for sensing purposes. Some specific MIPs have been developed, based on non-covalent interactions template-functional monomers, and with the most common composition as far as the functional monomer and the cross-linker are concerned. In some cases, the MIP composition was optimized by computational methods considering different functional monomers and cross-linkers as well as possible interfering interactions. The MIPs characteristics, as the affinity constant, the capacity of uptake and selectivity have been evaluated by batch procedure and the flow procedure. Porous MIP particles and MIP beads have been considered and characterized by batch equilibration. In particular MIPs for sensing the following molecules have been developed and characterized: 2-FAL (2-furhaldehide) and dibenzyldisulfide (DBDS) because of their rising importance as useful markers of health status of the middle tension transformers in the large distribution energy. 2-FAL was considered in aqueous matrices too, in view of its relevance in food quality control. The optical sensors developed have been characterized by determining the adsorption isotherms on the polymeric layer, based on the sensor response. The sensors based on SPR appear to be really promising due to the optimal sensitivity, low cost and possibility of miniaturization by employing POFs. Moreover, a high selectivity and affinity constant (Kaff), a low LOD and the possibility of the re-use are provided by the successful implementation of MIPs as receptors. Similar optimal results have been obtained by the evanescent wave coupling (EWC) moreover this platform presents the advantages of avoiding the use of Au layer, so could be superior to the SPR ones for the better reproducibility. Also, new kinds of molecularly imprinted materials have been considered in order to improve the biocompatibility of the sensing devices. In particular silk fibroin has been examined for its good optical and mechanical characteristics. Moreover, it is a biomaterial already approved for biomedical applications. Preliminary results on the imprinting of fibroin with glucose have been promising, with an imprinting factor higher than one. Moreover, the imprinted material can easily obtain a thin layer, which is particularly suitable for sensor development.| File | Dimensione | Formato | |
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Tesi PhD Simone Marchetti.pdf
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https://hdl.handle.net/20.500.14242/85730
URN:NBN:IT:UNIPV-85730