Optoelectronic sensors based on molecularly imprinted polymers

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.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

Optical Sensors

This book is a compilation of works presenting recent developments and practical applications in optical sensor technology. It contains 10 chapters that encompass contributions from various individuals and research groups working in the area of optical sensing. It provides the reader with a broad overview and sampling of the innovative research on optical sensors in the world

Biosensors for cardiac biomarkers detection: a review

The cardiovascular disease (CVD) is considered as a major threat to global health. Therefore, there is a growing demand for a range of portable, rapid and low cost biosensing devices for the detection of CVD. Biosensors can play an important role in the early diagnosis of CVD without having to rely on hospital visits where expensive and time-consuming laboratory tests are recommended. Over the last decade, many biosensors have been developed to detect a wide range of cardiac marker to reduce the costs for healthcare. One of the major challenges is to find a way of predicting the risk that an individual can suffer from CVD. There has been considerable interest in finding diagnostic and prognostic biomarkers that can be detected in blood and predict CVD risk. Of these, C-reactive protein (CRP) is the best known biomarker followed by cardiac troponin I or T (cTnI/T), myoglobin, lipoprotein-associated phospholipase A(2), interlukin-6 (IL-6), interlukin-1 (IL-1), low-density lipoprotein (LDL), myeloperoxidase (MPO) and tumor necrosis factor alpha (TNF-α) has been used to predict cardiovascular events. This review provides an overview of the available biosensor platforms for the detection of various CVD markers and considerations of future prospects for the technology are addressed

Surface Plasmon Resonance for Biosensing

The rise of photonics technologies has driven an extremely fast evolution in biosensing applications. Such rapid progress has created a gap of understanding and insight capability in the general public about advanced sensing systems that have been made progressively available by these new technologies. Thus, there is currently a clear need for moving the meaning of some keywords, such as plasmonic, into the daily vocabulary of a general audience with a reasonable degree of education. The selection of the scientific works reported in this book is carefully balanced between reviews and research papers and has the purpose of presenting a set of applications and case studies sufficiently broad enough to enlighten the reader attention toward the great potential of plasmonic biosensing and the great impact that can be expected in the near future for supporting disease screening and stratification

Design and Analysis of Advanced Photonic Devices for Electromagnetic Transmission and Sensing

In this thesis, we report the investigation of advanced photonic devices for electromagnetic transmission and biochemical sensing in the terahertz and optical regimes. The choice of material for designing a terahertz device is deemed to be one of the most crucial factors. First, we consider materials that are frequently used in making terahertz devices. We experimentally demonstrate the optical, thermal, and chemical properties of various chosen glasses, polymers, and resin to select the optimal material for terahertz. Second, we perform a broad review on terahertz optical fibres—this includes various fibre categories, their guiding mechanisms, fabrication methodologies, possible experimental methodologies, and applications. Third, we analyse and demonstrate the design of various fibre structures for terahertz transmission and sensing, and then perform experiments on a hollow core antiresonant fibre. We demonstrate successful fabrication of an asymmetrical Zeonex fibre using a novel fabrication method. This is carried out by using a tabletop horizontal extruder designed for producing polymer filaments. The fabricated fibre is then experimentally investigated for terahertz transmission and gas sensing. Fourth, we study optical fibre based surface plasmon resonance biosensors for operation in the optical regime. Theoretical studies are undertaken to obtain the best possible sensor in consideration of performance, experimental feasibility, and fabrication. One of the optimized sensors is then fabricated as a possible candidate for possible realworld sensing applications. Finally, we study metasurface planar devices for achieving high sensitivity and quality factor in the terahertz regime. We first demonstrate a tunable graphene metasurface that can achieve multi-band absorption and high refractometric sensing. Later, we demonstrate on an all-dielectric metasurface that reports highest Q-factor in the terahertz regime. We fabricate and experiment on the dielectric metasurface and find good agreement with the simulation.Thesis (Ph.D.) -- University of Adelaide, School of Electrical & Electronic Engineering, 202

Localized surface plasmon resonance for biosensing lab-on-a-chip applications

In recent times, metallic nanoparticle plasmonics coupled with applications towards biosensing has gathered momentum to the point where commercial R&D are investing large resources in developing the so-called localized surface plasmon resonance (LSPR) biosensors. Conceptually, the main motivation for the research presented within this thesis is achievement of fully-operational LSPR biosensor interfaced with the state-of-the-art microfluidics, allowing for very precise control of sample manipulation and stable read-out. LSPR sensors are specifficaly engineered by electron beam lithography nanofabrication technique, where nanoparticle interactions are optimized to exhibit increased sensitivity and higher signal-to-noise ratio. However, the overall performance of LSPR lab-on-a-chip device depends critically on the biorecognition layer preparation in combination with surface passivation. As an introduction, the principles of plasmonic biosensing are identified encompassing both Surface Plasmon Resonance (SPR) and Localized SPR. Being successfully implemented into commercial product, the governing physics of SPR is compared to LSPR in chapter 1, together with advantages and disadvantages of both. Chapter 2 describes methods necessary for LSPR biosensor development, beginning with nano-fabrication methods, the modelling tool (COMSOL Multiphisics), while the basics of micro-fabrication in microfluidics conclude this chapter, where passive and active microfluidics networks are discerned. Particularly attractive optical properties are exhibited by closely-coupled nanoparticles (dimers), with the dielectric gap of below tens of nm, which were theoretically predicted to be very suitable as LSPR biosensing substrates. Chapter 3 is subjected to optical characterization (dependence on the size of the dielectric gap) of nanofabricated dimer arrays. The acquired data demonstrate the advantages of the nanofabrication methods presented in chapter 2 and the technique for fast and reliable determination of nanoparticle characteristic parameters. The initial biosensing-like experiments presented in chapter 4 (no integration with microfluidics) proved for the first time, the theoretical predictions of higher sensitivity, yielding additionally the specific response as function of analyte size and dielectric gap between nanoparticles. The overall response of different dimer arrays (various gaps) provides information about adopted conformation of analyte protein once immobilized. Broad resonances of dimers feature higher noise when employing them for the real-time LSPR biosensing. As a way to circumvent such problem, the feasibility of employing far-field interaction within the nanoparticle array to spectrally narrow resonance is investigated in chapter 5 by optimizing the array periodicity and introducing thin waveguiding layers. Finally, the concluding chapter 6 is dedicated to a full assembly of a Lab-on-a-chip (LOC) LSPR biosensor, starting with interfacing plasmonic substrates with compatible active microfluidic networks, allowing the precise sample delivery and multiplexing. The prototype device consisting of 8 individual sensors is presented with typical modes of operation. The bulk refractive index determination of various samples demonstrates the working principle of such device. Finally, various strategies of biorecognition layer formation are discussed within the on-going research