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

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

Real-Time Water Quality Monitoring with Chemical Sensors

Water quality is one of the most critical indicators of environmental pollution and it affects all of us. Water contamination can be accidental or intentional and the consequences are drastic unless the appropriate measures are adopted on the spot. This review provides a critical assessment of the applicability of various technologies for real-time water quality monitoring, focusing on those that have been reportedly tested in real-life scenarios. Specifically, the performance of sensors based on molecularly imprinted polymers is evaluated in detail, also giving insights into their principle of operation, stability in real on-site applications and mass production options. Such characteristics as sensing range and limit of detection are given for the most promising systems, that were verified outside of laboratory conditions. Then, novel trends of using microwave spectroscopy and chemical materials integration for achieving a higher sensitivity to and selectivity of pollutants in water are described

Fabrication of 3D electrodes for biosensor applications

Alzheimer’s Disease is one of the most common forms of dementia, affecting millions of people worldwide. Although incurable, an easy and effective form of diagnosis is still missing. Thus, this work aims to develop an electrochemical biosensor for the early detection of Alzheimer's disease, by recognizing the peptide Aβ-42, a biomarker associated with visible differences in the brain tissue and responsible for the formation of senile plaques. The intended sensing devices use a bottom-up designing approach, having paper as substrate. Paper is one of the most promising materials in the current flexible electronics industry, for being eco-friendly, cheap, abundant and offering biocompatible, easy and fast construction procedures. The biosensors produced herein use pencil and printed carbon electrodes, allied with laser writing techniques. The electrical circuits are designed either on a conductive carbon ink or a 9B pencil tracks, printed or draw directly on the substrate. The recognition is done by a molecularly imprinted polymer, created on the electrode’s surface by electropolymerizing a mixture of the analyte (Aβ-42) and a monomer (O-Phenylenediamine). This pro-cess forms a conductive polymer with recognition sites displaying affinity for the selected biomarker. The parameters involved in the electropolymerization were optimized, by imprinting the peptide on the sensing layer, growing the polymer around the Aβ-42 peptide and removing it later by incubating in suitable enzyme and acid solutions. The performance of the biosensor was evaluated by electroanalytical techniques. The analytical features of the biosensor were further evaluated by electroanalytical techniques. For this purpose, the analytical response was tested with standard solutions ranging from 0.1 ng/mL to 1μg/mL of Aβ-42 in PBS buffer and Cormay Serum. The response was found of analytical interest, considering that healthy individuals show normal values of ~23.3 pg/mL. Overall, the developed biosensor offered numerous benefits, such as being a low cost, having reusa-bility features, with a reproducible and fast response, which may have a strong impact in the early de-tection of Alzheimer disease

Applications of Molecularly Imprinted Films

Molecularly imprinted polymers are materials that have voids that are complementary in shape, size, and electronic environment to a specific molecule used for preparation, known as the template. These voids are specific recognition sites that bind the templates preferentially and are used specifically for biomimetic sensors and for solid-phase extraction. Because the specific surface is very important during this process, the use of films and membranes is preferred. This book contains four articles dedicated to sensor application (three research articles and one review) and one research article dedicated to solid-phase extraction

Molecularly Imprinted Polymers for Chemical Detection on a Paper Substrate

Molecularly imprinted polymers (MIPs) have become one of the most promising materials for achieving superior performance in detecting numerous biological molecules, chemical compounds, and water pollutants. Integrated with a paper substrate, MIPs can be fabricated into a paper-based sensor that is low-cost, flexible, and easy to be processed and modified. In this study, we have demonstrated the detection of two typical perfluorinated compounds (PFCs), perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), with the molecularly imprinted polyaniline (MIP-PANI) paper sensor platform. The detection limits of PFOA (20.55 ppt) and PFOS (7.12 ppt) with linear ranges of 1–200 ppt have been estimated. In addition, the surface of the MIP structure upon exposure to PFCs was characterized to propose the detection mechanism and visualize the molecular imprinting process. We also demonstrated the integration of MIP-PANI with ultra-high frequency (UHF) wireless communication function for detecting multiple volatile organic compounds such as ammonia and ethanol. Wireless responses of the reduced reflection coefficient as a function of frequency are summarized, and the potential characteristic peaks and regions with trends in gas concentrations were identified. The calibration curves using a linear regression model were calculated to estimate the limit of detection of ammonia gas, which is 122 ppb. To further expand the applications of the MIP-PANI platform, lentiviruses were imprinted in the polymer electrode. The calibration curve showed a considerably better signal response upon exposure to virus samples compared with the non-molecularly imprinted control, suggesting its potential in biomedical sensing. This paper-based sensor incorporated with molecularly imprinted polymer electrodes adapts to various chemical as well as biological compounds with excellent sensitivity and selectivity at a low-cost compared with conventional assays, providing the potential in environmental monitoring and biomedical applications

Cellulose-Based Biosensing Platforms

Cellulose empowers measurement science and technology with a simple, low-cost, and highly transformative analytical platform. This book helps the reader to understand and build an overview of the state of the art in cellulose-based (bio)sensing, particularly in terms of the design, fabrication, and advantageous analytical performance. In addition, wearable, clinical, and environmental applications of cellulose-based (bio)sensors are reported, where novel (nano)materials, architectures, signal enhancement strategies, as well as real-time connectivity and portability play a critical role

Paper-based microfluidic devices for food adulterants: Cost-effective technological monitoring systems

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGAnalytical sciences have witnessed emergent techniques for efficient clinical and industrial food adulterants detection. In this review, the contributions made by the paper-based devices are highlighted for efficient and rapid detection of food adulterants and additives, which is the need of the hour and how different categories of techniques have been developed in the past decade for upgrading the performance for point-of-care testing. A simple strategy with an arrangement for detecting specific adulterants followed by the addition of samples to obtain well-defined qualitative or quantitative signals for confirming the presence of target species. The paperbased microfluidics-based technology advances and prospects for food adulterant detection are discussed given the high-demand from the food sectors and serve as a valued technology for food researchers working in interdisciplinary technological frontiers.Vision Group on Science and Technology, Government of Karnataka | Ref. KSTePS/ VGST/SMYSR-2016–17/GRD-595/2017–18Vision Group on Science and Technology, Government of Karnataka | Ref. KSTePS/VGSTRGS/F/GRD No.711/2017–18Science and Engineering Research Board (SERB), Department of Science and Technology, Govt of India | Ref. CRG/2020/00306

Recent progress in nanocomposites based on conducting polymer: application as electrochemical sensors

Abstract Over the years, intensive research works have been devoted to conducting polymers due to their potential application in many fields such as fuel cell, sensors, and capacitors. To improve the properties of these compounds, several new approaches have been developed which consist in combining conducting polymers and nanoparticles. Then, this review intends to give a clear overview on nanocomposites based on conducting polymers, synthesis, characterization, and their application as electrochemical sensors. For this, the paper is divided into two parts: the first part will highlight the nanocomposites synthesized by combination of carbon nanomaterials (CNMs) and conducting polymers. The preparation of polymer/CNMs such as graphene and carbon nanotube modified electrode is presented coupled with relevant applications. The second part consists of a review of nanocomposites synthesized by combination of metal nanoparticles and conducting polymers