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.

We introduce a very simple technique to obtain aligned carbon nanotube arrays tested in organic thin-film transistors based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as the organic semiconductor. The technique to prepare aligned CNT electrode arrays was simple and resulted in organic thin-film transistors with a higher drain-source current and lower threshold voltage proving their effectiveness as injection electrodes. We believe that the aligned carbon nanotube electrode array can find important applications in organic microelectronic and biosensor devices.

The n-type organic semiconductor phenyl-C-61-butyric acid methyl ester (PCBM), a soluble fullerene derivative well investigated for organic solar cells and transistors, can undergo several successive reversible, diffusion-controlled, one-electron reduction processes. We exploited such processes to shed light on the correlation between electron transfer properties, ionic and electronic transport as well as device performance in ionic liquid (IL)-gated transistors. Two ILs were considered, based on bis(trifluoromethylsulfonyl)imide [TFSI] as the anion and 1-ethyl-3-methylimidazolium [EMIM] or 1-butyl-1-methylpyrrolidinium [PYR14] as the cation. The aromatic structure of [EMIM] and its lower steric hindrance with respect to [PYR14] favor a 3D (bulk) electrochemical doping. As opposed to this, for [PYR14] the doping seems to be 2D (surface-confined). If the n-doping of the PCBM is pursued beyond the first electrochemical process, the transistor current vs. gate-source voltage plots in [PYR14][TFSI] feature a maximum that points to the presence of finite windows of high conductivity in IL-gated PCBM transistors.

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.

The electrical properties of eumelanin, a ubiquitous natural pigment, have fascinated scientists since the late 1960s. For several decades, the hydration-dependent electrical properties of eumelanin have mainly been interpreted within the amorphous semiconductor model. Recent works undermined this paradigm. Here we study protonic and electronic charge carrier transport in hydrated eumelanin in thin film form. Thin films are ideal candidates for these studies since they are readily accessible to chemical and morphological characterization and potentially amenable to device applications. Currentvoltage (I-V) measurements, transient current measurements with proton-transparent electrodes, and electrochemical impedance spectroscopy (EIS) measurements are reported and correlated with the results of the chemical characterization of the films, performed by X-ray photoelectron spectroscopy. We show that the electrical response of hydrated eumelanin films is dominated by ionic conduction (10(-4)10(-3) S cm(-1)), largely attributable to protons, and electrochemical processes. To propose an explanation for the electrical response of hydrated eumelanin films as observed by EIS and I-V, we considered the interplay of proton migration, redox processes, and electronic transport. These new insights improve the current understanding of the charge carrier transport properties of eumelanin opening the possibility to assess the potential of eumelanin for organic bioelectronic applications, e.g. protonic devices and implantable electrodes, and to advance the knowledge on the functions of eumelanin in biological systems.

Electrolyte-Gated (EG) transistors, making use of electrolytes as the gating medium, are interestingfor their low operation voltage. Furthermore, EG polymer transistors offer the advantage of solution processing, low cost, and mechanical flexibility. Despite the intense research activity in EG transistors, clear guidelines to correlate the properties of the materials used for the transistor channel and electrolytes with the doping effectiveness of the transistor channel are yet to be clearly established. Here, we investigate the use of room temperature ionic liquids (RTILs) based on the [TFSI] anion (namely, [EMIM][TFSI], [BMIM][TFSI], and [PYR14][TFSI]), to gate transistors making use of MEH-PPV as the channel material. Morphological studies of MEH-PPV and RTIL films showed a certain degree of segregation between the two components. All the EG transistors featured clear drain-source current modulations at voltages below 1V. Polar solvent additives as propylene carbonate were used to improve the transistor response time. (C) 2015 AIP Publishing LLC.

Electrolyte-gated (EG) organic transistors are interesting for their low voltage operation and versatile cost-effective fabrication and printability.1 Room temperature ionic liquids (RTILs) are attractive as gating media for their chemico-physical properties, such as ionic conductivity up to 10 mS·cm-1, negligible volatility, and electrochemical stability windows up to ca 5 V.2 The availability of RTILs with different molecular structures gives the possibility to control specifically the interactions between the ions constituting the RTIL and the channel material in view of an optimized doping. Clear guidelines to establish an effective doping as a function of the ions constituting the electrolyte, are yet to be established. In this work we report on EG transistors with phenyl-C61-butyric acid methyl ester (PCBM), as the channel material, and room temperature ionic liquids based on bis(trifluoromethylsulfonyl)imide ([TFSI]) anion, as the gating medium. The cations constituting the ionic liquids were 1-ethyl-3-methylimidazolium ([EMIM]), 1-butyl-3-methylimidazolium ([BMIM]) or 1-butyl-1-methylpyrrolidinium ([PYR14]). Electrical measurements show that the cation strongly affects the behavior of n-type EG PCBM transistors. The higher charge carrier mobility, lower on/off ratio and faster response time obtained with [PYR14][TFSI]-gated transistors, suggests lower cation incorporation into the PCBM channel material. [EMIM][TFSI]- and [BMIM][TFSI]-gated PCBM transistors featured similar electric behavior, coherent with the similar molecular structure of the cations. 1. S. H. Kim et al., Adv. Mater. Weinheim, 25, 1822–1846 (2013). 2. M. Galiński, A. Lewandowski, and I. Stępniak, Electrochim. Acta, 51, 5567 (2006).

We report the proof-of-concept of the TransCap, a monolithically integrated device that exhibits the storage properties of a supercapacitor and the low-voltage operation of an electrolyte-gated transistor. The proof-of-concept is based on coupling a polymer channel with a high surface area carbon gate, employing an ionic liquid as the electrolyte. The possibility to recover the stored energy from the TransCap permits us to use it to power different microelectronic components.

Electrolyte-gated (EG) transistors permit to achieve current modulations of several orders of magnitude at relatively modest gate voltages, by exploiting the exceptionally high capacitance of electrical double layer forming at the electrolyte/transistor channel interface. Different doping mechanisms have been proposed to explain the gating process in EG transistors. For organic polymers, the common doping mechanism is faradic, depends on the channel electrical potential and the doping charge is about two orders of magnitude larger than for electrostatically doped non-porous materials. Moreover, organic channel and electrolyte have to be selected taking into account that channel modulation has to be performed by applying gate-source voltages (V gs ) which are compatible with the electrochemical stability window of the electrolyte. Ionic liquid electrolytes, for their exceptionally high chemical and electrochemical stability and good conductivity at room temperature are of interest as electrolyte gating media in EG transistor. The faradic nature of the polymer channel doping also requires the use of gate electrode materials that are non-limiting in terms of their capability to supply the charge required for channel modulation within the electrochemical stability window of the electrolyte. We targeted the use of high surface area carbons as gate electrode materials because of their capability to electrostatically supply the charge required to dope organic polymer transistor channels, within narrow electrode potential excursion. Here, we report on a new generation of low voltage EG transistors making use of a low-cost, high surface area gate electrode, an organic electronic polymer, like MEH-PPV (poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene), as the channel material and ionic liquid, like [EMIM][TFSI] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), as the electrolyte gating medium. Using such configuration, is it possible to apply V gs biases lower than 1.0 V to achieve effective channel modulations (ON/OFF ratio larger than 10 3 ) and hole mobility of about 10 -3 cm 2 V -1 s -1 . Acknowledgement This work was financially supported by NSERC (Discovery grants, CS and FC) and FQRNT (Nouveau Chercheur, CS). JS acknowledges financial support by CONACYT. References [1] J. Sayago, F. Soavi, F. Cicoira, C. Santato , Adv. Mater., submitted.

The use of high surface area, low cost, activated carbon gate electrodes enables low voltage (sub-1 V) operation in ionic liquid-gated organic transistors and renders unnecessary the presence of an external reference electrode to monitor the channel potential.

Multifunctional organic materials can be used to make optically tunable organic transistors that can operate on microsecond timescales, thus opening new perspectives in the design of organic integrated circuits.