Transistors as an Emerging Platform for Portable Amplified Biodetection in Preventive Personalized Point‐of‐Care Testing

The impressive improvement in biomolecular detection has gone from simple chemical methods to sophisticated high throughput laboratory machines capable of accurately measuring the complex biological components and interactions. In the following chapter, we focus our attention on transistor‐based devices as an emerging platform for easy‐to‐use, portable amplified biodetection for preventive personalized medical applications and point‐of‐care testing. Electronic sensing devices comprise biosensors based on field‐effect transistors (bio‐FETs) and organic electrochemical transistors (OECTs). Transistor sensing devices can transduce electronic and ionic signals thereby creating an effective human‐machine communication channel. In this chapter, we survey the progress done on the development of transistor innovative concepts to examine biological processes, i.e., biosensors integrated with textiles, flexible substrates, and biocompatible materials. Electrochemical and field‐effect transistors can operate at low voltages possibly serving for highly sensitive, selective, and real‐time sensing devices. The exploration of biosensors integrates different disciplines such as organic electronics, biology, electrochemistry, and materials science

New Materials and Processing Routes for Organic Electrochemical Transistors

La bioélectronique est un domaine pluridisciplinaire dont l’objectif est le couplage des dispositifs électroniques avec les systèmes biologiques. La bioélectronique vise l’exploitation des dispositifs électroniques pour des applications biologiques, comme les systèmes de livraison de médicament implantables, la peau artificielle, ou encore les capteurs capables d’opérer in vivo ou in vitro. Les interfaces entre la biologie et l’électronique nécessitent des dispositifs qui soient à la fois mécaniquement flexibles et étirables, chimiquement inertes, ainsi que, dans certains cas, biodégradables. La bioélectronique basée sur des matériaux organiques, ou bioélectronique organique, donne les moyens technologiques de produire des dispositifs électroniques mécaniquement flexibles ou dégradables, le tout à faible coût sur de larges surfaces. Les recherches intensives dans le domaine de l’électronique organique ont commencé dans les années ‘90, avec les premières diodes électroluminescentes, transistors ainsi que cellules photovoltaïques basés sur des matériaux organiques. Les dispositifs électroniques organiques deviennent omniprésents dans notre société moderne avec l’introduction sur le marché d’écrans basés sur l’utilisation de diodes électroluminescentes pour les téléphones cellulaires, les télévisions et d’autres produits commerciaux. D’autres dispositifs électroniques organiques, tels que les transistors organiques pour les tags d’identification radiofréquence, devraient faire à leur tour une entrée sur le marché dans un futur proche. Les matériaux organiques électroniques présentent plusieurs avantages sur leurs homologues inorganiques, ce qui les rend plus adaptés à certaines applications spécifiques. L’un des avantages les plus importants réside sans doute dans la capacité des matériaux organiques électroniques à transporter les porteurs de charge ioniques et électroniques, pour pouvoir développer de nouveaux dispositifs faisant l’interface avec les systèmes biologiques. Le transistor organique électrochimique (OECT), qui a trouvé de nombreuses applications dans les biocapteurs ou dans les dispositifs implantables, en est un bon exemple. Les OECTs offrent la capacité prometteuse à opérer à de faibles voltages (<1 V) en solutions aqueuses, où les procédés biologiques ont lieu. Les OECTs peuvent être réalisés entièrement à l’aide de polymères conducteurs et sont composés d’électrodes appelées source et drain, ainsi que d’un canal en contact ionique avec une électrode appelée grille via une solution électrolytique. Le potentiel appliqué à la grille module le courant qui circule dans le canal. Dans ix la plupart des OECTs, l’application d’une différence de potentiel positive à la grille induit une redistribution réversible des ions positifs à l’intérieur du polymère conducteur composant le canal, ainsi qu’à l’intérieur de l’électrolyte. Ceci, couplé avec l’injection de charges par la source et le drain, résulte en un dédopage électrochimique du canal conducteur, qui s’accompagne d’une diminution du courant source-drain. Dans cette thèse, nous décrivons la fabrication de différents types d’OECTs, rigides, flexibles ou encore dégradables, sur des substrats de verre, de plastique ou de shellac dégradable. Des techniques non-conventionnelles comme la gravure sur parylène et la photolithographie orthogonale ont été utilisées pour la fabrication des dispositifs. Ces méthodes permettent d’éviter le contact direct entre les matériaux organiques et d’autres matériaux (i.e. les photorésines, les solvants et les décapants) typiquement utilisés en photolithographie, évitant ainsi une dégradation des propriétés électriques. Afin de mieux comprendre le mécanisme de fonctionnement des OECTs, qui est toujours largement méconnu, ainsi que d’optimiser leurs performances, nous avons étudié le rôle de leurs composants clé, i.e. l’électrolyte, l’électrode de grille et le substrat. Nous avons aussi exploré la possibilité de fabriquer un dispositif flexible intégrant un transistor et un supercondensateur, qui pourrait être intéressant pour des applications dans le domaine du micro-stockage d’énergie. Les liquides ioniques (ILs) sont des candidats intéressants pour servir de milieu de grille (gating medium) dans les OECTs. Néanmoins, les ILs présentent une viscosité excessivement élevée qui empêche de les utiliser directement dans les OECTs. Nous rapportons ici deux approches permettant d’utiliser le liquide ionique hautement visqueux triisobutyl(méthyl)phosphonium tosylate (Cyphos® IL 106) dans des OECTs basés sur le poly(3,4-éthylènedioxythiophène) polystyrènesulfonate (PEDOT:PSS). Ces deux approches sont l’utilisation d’un mélange binaire IL-H2O et l’utilisation de gels ioniques. Ces formulations du milieu de grille mènent à une augmentation de la modulation de l’OECT, comparativement aux résultats obtenus avec le liquide ionique pur. En utilisant des grilles en carbone activé de grande surface, des ratios ON/OFF allant jusqu’à 5000 ont été obtenus avec les mélanges Cyphos® IL 106–H2O à 5% et 10% de H2O, v/v. Des OECTs planaires utilisant du PEDOT:PSS comme matériau pour le canal, du carbone nanostructuré comme matériau pour l’électrode de grille et du gel poly(sodium 4-styrènesulfonate) x (PSSNa) comme électrolyte ont été fabriqués sur des substrats flexibles de poly(téréphtalate d'éthylène) (Mylar®). Le carbone nanostructuré a été déposé à température ambiante par déposition supersonique de faisceaux en agrégats (SCBD). L’OECT résultant se comporte comme un supercondensateur hybride (ce qui donne un dispositif que nous avons appelé transcap). La capacité à stocker l’énergie des transcaps a été étudiée dans deux configurations : l’une utilise le PEDOT:PSS comme électrode positive et le carbone nanostructuré comme électrode negative, tandis que la deuxième configuration inverse la polarité des électrodes. Les études de la charge/décharge potentiostatique révèlent que les deux supercondensateurs montrent de bonnes performances en termes de rétention de voltage. Ceci est particulièrement vrai quand du PEDOT:PSS est utilisé comme électrode positive. Les caractéristiques de la charge/décharge galvanostatique présentent une forme triangulaire symétrique typique, ce qui indique un comportement capacitif quasiment idéal, avec une haute efficacité coulombienne (proche de 100%). Enfin, nous avons développé des OECTs “verts”, qui emploient des substrats dégradables et de l’eau comme milieu de grille. Des OECTs fabriqués sur du PET (polytéréphtalate d’éthylène) ont été transférés sur un substrat de shellac par transfer printing. Afin d’étudier l’effet de grille en présence d’eau comme milieu de grille, nous avons utilisé une électrode de grille en carbone activé ainsi qu’une électrode de grille en PEDOT:PSS. Les résultats ont montré que les OECTs utilisant des grilles en carbone activé présentent une réponse en courant plus lente et une modulation de courant plus élevée que les grilles en PEDOT:PSS. Le substrat en shellac peut être dégradé en utilisant une solution de KOH à une concentration 1 M. Nos études sur différents électrolytes, grilles de grande surface spécifique et substrats ont permis des avancées significatives dans le domaine des OECTs, qui vont mener vers de nouvelles applications in vivo et in vitro. De plus, les OECTs peuvent être utilisés comme des dispositifs de stockage d’énergie. Le concept de transcap intégrant un transistor organique électrochimique et un supercondensateur peut être davantage optimisé pour obtenir des temps de réponse plus rapides et une autodécharge plus faible, ainsi que des propriétés électriques et de stockage d’énergie optimisées. ---------- Organic electronics, which use thin films or single crystals of organic π-conjugated materials as semiconductors, enable technologies for large-area, mechanically flexible and low-cost electronics. Intense research in organic electronics started in the 90s, with the demonstration of the first lightemitting diodes, transistors and solar cells based on organic materials. Today, such devices are becoming ubiquitous in our society as they can be found in displays based on organic lightemitting diodes in mobile phones, televisions and many other consumer devices. Other organic electronic devices, such as transistors for radio frequency identification tags, are expected to enter the market in the near future. Organic electronic materials present several advantages over inorganic ones, which make them more viable for targeted applications. One the most significant advantages of organic materials is their ability to transport both ionic and electronic charges, which can be exploited in bioelectronics, a multidisciplinary field that deals with the coupling of electronic devices with biological systems. The primary goal of bioelectronics is to exploit electronic devices for biological applications, such as implants, drug delivery systems, artificial skin, and sensors for in vivo or in vitro environments. Interfaces between biological systems and electronics require devices that are mechanically flexible and stretchable, chemically inert and in some cases biodegradable. Bioelectronics based on organic materials, known as organic bioelectronics, especially promising because promise to yield devices that are able to combine ionic and electronic transport and to offer improved mechanical interfaces with living tissues, due to the soft nature of the polymer surface. An example of a bioelectronic device is the organic electrochemical transistor (OECT), which has found applications in biosensors and implantable devices. OECTs are attractive because of their ability to operate at low voltages (< 1 V) in aqueous solutions, where biological processes take place. OECTs can be composed solely of conducting polymers and consist of source and drain electrodes and a channel in ionic contact with a gate electrode via an electrolyte solution. vi The gate voltage modulates the current flowing in the channel. In most OECTs, the application of a positive gate bias induces a reversible redistribution of positive ions within the conducting polymer channel and the electrolyte. This, together with charge injection from source and drain, results in electrochemical dedoping of the conducting channel, accompanied by a decrease of the source-drain current. In this thesis, we have fabricated rigid, flexible and degradable OECTs on glass, plastics and degradable shellac substrates. Unconventional techniques such as parylene patterning and orthogonal photolithography have been used for device fabrication. These processing techniques let us avoid placing organic materials in contact with other materials (such as photoresists, solvents and strippers) typically used in photolithography, which can result in the degradation of the electrical properties of the organics. To understand how OECTs work and to optimize their performance, we have investigated the role of their main components (electrolyte, gate electrode and substrate). Moreover, we have realized a flexible device integrating a transistor and a supercapacitor, for applications in energy micro-storage. Ionic liquids (ILs) are interesting candidates as gating media in OECTs. However, ILs can exhibit excessively high viscosity that prevents their straightforward use. We report two ways to employ the highly viscous ionic liquid triisobutyl(methyl)phosphonium tosylate (Cyphos® IL 106) in OECTs based on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS), namely IL–H2O binary mixtures and ion gels. The use of these formulations as gating media increases the OECT modulation with respect to experiments where pure ionic liquids are used. Using high surface area activated carbon gates, we achieved ON/OFF ratios as high as 5000 with Cyphos® IL 106–H2O mixtures at 5 and 10% H2O v/v. Planar OECTs using PEDOT:PSS as the channel material, nanostructured carbon as the gate electrode material and poly(sodium 4-styrenesulfonate (PSSNa) gel as the electrolyte were fabricated on flexible polyethylene terephthalate (Mylar®) substrates. Nanostructured carbon was deposited at room temperature by supersonic cluster beam deposition (SCBD). Interestingly, the OECT acts as a hybrid supercapacitor to give a device that we called transcap. The energy storage ability of transcaps has been studied with two configurations: one features PEDOT:PSS vii as the positive electrode and nanostructured carbon as the negative electrode; the other has a reversed electrode polarity. Potentiostatic charge/discharge studies show that both supercapacitors show good performance in terms of voltage retention, particularly when PEDOT:PSS is used as the positive electrode. Galvanostatic charge-discharge characteristics show typical symmetric triangular shape, indicating a nearly ideal capacitive behaviour with a columbic efficiency close to 100%. Finally, we developed “green” OECTs, which employ degradable substrates and water as the gating medium. OECTs were patterned onto degradable shellac substrates by transfer printing. To explore the gate effect in presence of water as the gating medium, we have employed AC gate electrodes and PEDOT:PSS gate electrodes. Results indicate that OECTs with AC gates have slower current response and higher current modulation than those with PEDOT:PSS gates. The shellac substrate can be degraded in 1 M KOH solution. Our study of various electrolytes, high specific surface area gates and diverse substrates has significantly advanced the knowledge in the field of OECTs, thereby paving the way to applications in vivo and in vitro. Interestingly, OECTs can be used as energy storage devices. The concept of a transcap integrating an organic electrochemical transistor and a supercapacitor can be further optimized to achieve faster time responses, decreased self-discharge and optimized electrical and energy storage properties

Safe storage guidelines for soybeans at different temperatures and moisture contents: Poster

Poor storage capacity of soybean makes it prone to fungal spoilage and heating during storage, resulting in lower quality. Early prediction of the fungal spoilage in stored soybeans is very difficult because fungi are often too small to be seen with the naked eye. Here a new method for fungus to early detection is adopted: it is called counting fungal spores. Soybeans with moisture contents of 11.4, 12.1, 13.0, 13.9, 14.3 and 14.7%, were held at 6 temperatures 10, 15, 20, 25, 30 and 35? for180d. Samples were taken at regular intervals and the fungal spores counted. The safe storage conditions (temperature, moisture content, duration) were estimated by means of a curve fitted using the power function fitting. It can predict of soybean spoilage by fungus before there is visible damage.Poor storage capacity of soybean makes it prone to fungal spoilage and heating during storage, resulting in lower quality. Early prediction of the fungal spoilage in stored soybeans is very difficult because fungi are often too small to be seen with the naked eye. Here a new method for fungus to early detection is adopted: it is called counting fungal spores. Soybeans with moisture contents of 11.4, 12.1, 13.0, 13.9, 14.3 and 14.7%, were held at 6 temperatures 10, 15, 20, 25, 30 and 35? for180d. Samples were taken at regular intervals and the fungal spores counted. The safe storage conditions (temperature, moisture content, duration) were estimated by means of a curve fitted using the power function fitting. It can predict of soybean spoilage by fungus before there is visible damage

Tackling the Problem of Dangerous Radiation Levels with Organic Field-Effect Transistors

Accurate, quantitative measurements of ionizing radiation, commonly employed in medical diagnostic and therapeutic applications are essential prerequisites to minimize exposure risks. Common examples of radiation detectors include ionization chambers, thermoluminescent dosimeters, and various semiconductor detectors. Semiconductor dosimeters such as p/n type silicon diodes and MOSFETs have found widespread adoption due to their high sensitivity and easy processing. A significant limitation of these devices, however, is their lack of tissue equivalence. The high atomic number (relative to soft tissue) of silicon causes these devices to over-respond to photon beams that include a significant low energy component, for example, 1–10 kV, due to an enhanced photoelectric interaction coefficient. Organic field effect transistors (OFETs) are capable of providing tissue equivalent response to ionizing radiation in order to monitor more accurately the risk of exposure in medical treatments. This chapter presents the possibility to use different types of OFETs as ionizing and X-ray radiation dosimeters in medical applications

Poly[[diaqua-μ2-4,4′-bipyridyl-μ2-o-phthalato-nickel(II)] dihydrate]

In the title layer complex, {[Ni(C8H4O4)(C10H8N2)(H2O)2]·2H2O}n, the Ni atom has a distorted octa­hedral environment, defined by the phthalate and 4,4′-bipyridyl ligands which link the Ni atoms, forming a square lattice in the bc plane. This extends into a three-dimensional supra­molecular network through O—H⋯O hydrogen-bonding inter­actions. The Ni atom lies on, and both ligands are bis­ected by, a crystallographic twofold axis

Poly[bis­(2,2′-bipyridine-κ2 N,N′)deca-μ-oxido-dioxidodicopper(II)tetra­vanadium(V)]

The title compound, [Cu2V4O12(C10H8N2)2]n, shows a two-dimensional copper–vanadate layer composed of eight-membered rings, each containing four corner-sharing VO4 tetra­hedra; these are linked through six penta­coordinated CuII atoms with the 2,2′-bipyridine ligands attached and pointing above and below the plane of the layer. The Cu atom is coordinated by two N donors from the 2,2′-bipyridine ligand and three O atoms from three adjacent VO4 units to form a distorted tetragonal pyramid. These layers are further connected by π–π inter­actions between inter­leaving bipyridine ligands of adjacent layers [centroid–centroid distances = 3.63 (1) and 3.68 (1) Å] into a three-dimensional supra­molecular structure

A New Architecture for Application-aware Cognitive Multihop Wireless Networks

In this article, we propose a new architecture for AC-MWN. Cognitive radio is a technique to adaptively use the spectrum so that the resource can be used more efficiently in a low-cost way. A multihop wireless network can be deployed quickly and flexibly without fixed infrastructure. In our proposed new architecture, we study backbone routing schemes with network cognition, and a routing scheme with network coding and spectrum adaptation. A testbed is implemented to test the proposed schemes for AC-MWN. In addition to basic measurements, we implement a video streaming application based on the proposed AC-MWN architecture using cognitive radios. Preliminary results demonstrate that the proposed AC-MWN is applicable, and is valuable for future low-cost and flexible communication networks