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The aim of the study is to open a new scope for organic electrochemical transistors based on PEDOT:PSS, a material blend known for its stability and reliability. These devices can leverage molecular electrocatalysis by incorporating small amounts of nano-catalyst during the transistor manufacturing (spin coating). This methodology is very simple to implement using the know-how of nanochemistry and results in efficient enzymatic activity transduction, in this case utilizing choline oxidase and glutamate oxidase.

Funding Agencies|EU [PIEF-GA-2011-301796]; Onnesjo foundation; Swedish Research Council [2002-4497]; Swedish Foundation for Strategic Research [IMF11-0052]; Knut and Alice Wallenberg Foundation [2012-0302]

Electrolyte-gated organic field-effect transistors have emerged in the field of biosensors over the last five years, due to their attractive simplicity and high sensitivity to interfacial changes, both on the gate/electrolyte and semiconductor/electrolyte interfaces, where a target-specific bioreceptor can be immobilized. This article reviews the recent literature concerning biosensing with such transistors, gives clues to understanding the basic principles under which electrolyte-gated organic field-effect transistors work, and details the transduction mechanisms that were investigated to convert a receptor/target association into a change in drain current.

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This review is divided into two parts; the first one summarizes the main features of surface modification by diazonium salts with a focus on most recent advances, while the second part deals with diazonium-based biosensors including small molecules of biological interest, proteins, and nucleic acids.

A new electrochemical methodology is reported for monitoring in homogeneous solution the enantiospecific binding of a small chiral analyte to an aptamer. The principle relies on the difference of diffusion rates between the targeted molecule and the aptamer/target complex, and thus on the ability to more easily electrochemically detect the former over the latter in a homogeneous solution. This electrochemical detection strategy is significant because, in contrast to the common laborious and time-consuming heterogeneous binding approaches, it is based on a simple and fast homogeneous binding assay which does not call for an aptamer conformational change upon ligand binding. The methodology is here exemplified with the specific chiral recognition of trace amounts of l- or d-tyrosinamide by a 49-mer d- or l-deoxyribooligonucleotide receptor. Detection as low as 0.1% of the minor enantiomer in a nonracemic mixture can be achieved in a very short analysis time (<1 min). The assay finally combines numerous attractive features including simplicity, rapidity, low cost, flexibility, low volume samples (few microliters), and homogeneous format.

Inkjet-printing is one of the most important fabrication techniques in the field of printed electronics. Its main advantages include the possibility of fabricating, at ambient conditions and by employing a digital layout, a large variety of electronic devices on different types of substrates, including flexible plastic ones. In this paper, the utilization of inkjet-printing as an important fabrication tool for the realization of organic transistors and circuits/sensing systems based on such type of transistors is reviewed. The most important aspects of the fabrication process, including ink formulation, printing deposition, and postprinting treatment, are described in detail. The most significant examples of inkjet-printed organic transistors of different types (field-effect, electrolytegated, and electrochemical) are presented and finally an overview of their applications as building blocks of more complex electronic circuits and systems for the detection and quantification of specific measurands is provided.

Ultrathin layers of thiophene derivatives were covalently attached to GC electrodes by electroreduction of diazonium salts. The films are densely packed structures and are able to mediate electron transfer above a threshold voltage tuned by the nature of the grafted molecules onto the electrode. We investigate the electron transfer properties of these layers by using electroactive probes having various redox potentials. Voltammetry and SECM measurements clearly show that for redox probes with low redox potentials diode-like behavior is observed and the current can flow in only one direction across these organic layers whereas, when the potential of the external redox probe increases, the transparency of the layers toward electron transfer in both direction increases (within the time range investigated). This behavior is not compatible with an EC cat mechanism, with electroactive immobilized centers characterized by a single redox potential E°I m , and clearly demonstrates the switching of the layer conductivity. In this sense, these layers are better modeled as covalently grafted conducting oligomers densely packed on the surface and capable of changing their charge transfer characteristics upon charge injection (i.e., doping of the grafted conjugated oligomers). The charge transfer mechanism of these ultrathin films is thus very different from that most of SAMs bearing an electroactive group, in which electron tunnelling through the monolayer is the main charge transfer mechanism.