The demand for real-time monitoring of cell functions and cell conditions has dramatically increased with the emergence of organ-on-a-chip (OOC) systems. However, the incorporation of co-cultures and microfluidic channels in OOC systems increases their biological complexity and therefore makes the analysis and monitoring of analytical parameters inside the device more difficult. In this work, we present an approach to integrate multiple sensors in an extremely thin, porous and delicate membrane inside a liver-on-a-chip device. Specifically, three electrochemical dissolved oxygen (DO) sensors were inkjet-printed along the microfluidic channel allowing local online monitoring of oxygen concentrations. This approach demonstrates the existence of an oxygen gradient up to 17.5% for rat hepatocytes and 32.5% for human hepatocytes along the bottom channel. Such gradients are considered crucial for the appearance of zonation of the liver. Inkjet printing (IJP) was the selected technology as it allows drop on demand material deposition compatible with delicate substrates, as used in this study, which cannot withstand temperatures higher than 130 °C. For the deposition of uniform gold and silver conductive inks on the porous membrane, a primer layer using SU-8 dielectric material was used to seal the porosity of the membrane at defined areas, with the aim of building a uniform sensor device. As a proof-of-concept, experiments with cell cultures of primary human and rat hepatocytes were performed, and oxygen consumption rate was stimulated with carbonyl-cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP), accelerating the basal respiration of 0.23 ± 0.07 nmol s-1/106 cells up to 5.95 ± 0.67 nmol s-1/106 cells s for rat cells and the basal respiration of 0.17 ± 0.10 nmol s-1/106 cells by up to 10.62 ± 1.15 nmol s-1/106 cells for human cells, with higher oxygen consumption of the cells seeded at the outflow zone. These results demonstrate that the approach of printing sensors inside an OOC has tremendous potential because IJP is a feasible technique for the integration of different sensors for evaluating metabolic activity of cells, and overcomes one of the major challenges still remaining on how to tap the full potential of OOC systems.

We report on the detailed electrical investigation of all-inkjet-printed thin-film transistor (TFT) arrays focusing on TFT failures and their origins. The TFT arrays were manufactured on flexible polymer substrates in ambient condition without the need for cleanroom environment or inert atmosphere and at a maximum temperature of 150 °C. Alternative manufacturing processes for electronic devices such as inkjet printing suffer from lower accuracy compared to traditional microelectronic manufacturing methods. Furthermore, usually printing methods do not allow the manufacturing of electronic devices with high yield (high number of functional devices). In general, the manufacturing yield is much lower compared to the established conventional manufacturing methods based on lithography. Thus, the focus of this contribution is set on a comprehensive analysis of defective TFTs printed by inkjet technology. Based on root cause analysis, we present the defects by developing failure categories and discuss the reasons for the defects. This procedure identifies failure origins and allows the optimization of the manufacturing resulting finally to a yield improvement.

1wileyonlinelibrary.com and easy-handling devices; however, numerous inherent problems still remain, especially concerning the long-term stability and lack of reliability, that require further studies and standardization before devices can be fully applied in fi eld applications. OTFTs are amenable to the use of multiple substrates and can operate at room temperature. They are especially interesting in biological applications, as they enable the use of a wide range of biocompatible and biodegradable materials detecting a wide range of analytes, including gases (such as NH 3 and NO 2 ), proteins, DNA, bacteria, etc. [ 5 ] However, the performance of these devices is limited by low sensitivity (around several micrograms per milliliter). Large surface-to-volume ratio nanostructures, high-k dielectrics, [ 6 ] or 1D materials such as silicon nanowires, carbon nanotubes, [ 7,8 ] and graphene have been used to enhance the sensitivity. Despite this fact, their fabrication has limitations, requiring sophisticated fabrication techniques to precisely deposit them. Solution-processed inorganic thin-fi lm devices may be promising; nevertheless, organic semiconductors benefi t from relatively low temperature, solution processing capability, and the fl exibility to work on any kind of substrate, with a high mobility. [ 9 ] Regardless of the organic high-performance materials, the limit of detection can be improved by means of: i) different geometries of the OTFT, and, ii) performing detection under the sub-threshold region. [ 10 ] Advances in organic electronics have yielded diverse, lowcost electronic components that have enabled the development of thin, fl exible, and environmental friendly devices. [ 11 ] Unlike traditional inorganic TFTs, which are made by a complicated photolithography processes that requires expensive masks and cleanroom facilities, OTFTs can be easily fabricated by inkjet printing and do not require cleanroom settings. Nevertheless, contemporary OTFTs suffer from certain drawbacks that researchers are currently endeavoring to overcome: high operating voltages, low material stability, and relatively short operating lifetimes.Among the OTFT-based devices, organic fi eld-effect transistors (OFETs) have been selected over organic electrochemical transistors (OECTs) for sensing purposes. The main factors motivating this choice are: i) dielectric functionalization without losing electrical properties of the organic semiconductors, and, ii) reusability device since the transduction mechanism is based on electrostatic gating consisting on a capacitive coupling between the organic semiconductor and the gate in contrast of the electrochemical doping/de-doping mechanism An Inkjet-Printed Field-Effect Transistor for Label-Free BiosensingMariana Medina-Sánchez , Carme Martínez-Domingo , Eloi Ramon , and

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Abstract-A high data capacity chipless radiofrequency identification (chipless-RFID) system, useful for security and authentication applications, is presented in this paper. Reading is based on near-field coupling between the tag, a chain of identical split ring resonators (SRRs) printed on a (typically flexible) dielectric substrate (e.g., liquid crystal polymer, plastic, paper, etc.), and the reader. Encoding is achieved by the presence or absence of SRRs at predefined (equidistant) positions in the chain, and tag identification is based on sequential bit reading. Namely, the tag must be longitudinally displaced, at short distance, over the reader, a microstrip line loaded with a SRR and fed by a harmonic signal. By this means, the harmonic signal is amplitude modulated, and the identification (ID) code is contained in the envelope function, which can be obtained by means of an envelope detector. With this system, tag reading requires proximity with the reader, but this is not an issue in many applications within the domain of security and authentication (e.g., secure paper for corporate documents, certificates, etc.). Several circularly-shaped 40-bit encoders (implemented in a commercial microwave substrate), and the corresponding reader, are designed and fabricated as proof-of-concept demonstrators. Strategies for programming the tags and a first proof-of-concept chipless-RFID tag fabricated on plastic substrate through inkjet printing are included in the paper.

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This paper presents a time-domain, chipless-RFID system with 80-bit tags inkjet-printed on ordinary DIN A4 paper. The tags, consisting of a linear chain of resonant elements (with as many resonators as the number of identification bits plus header bits), are read sequentially and by proximity (through near-field coupling). To this end, a transmission line, fed by a harmonic (interrogation) signal tuned to the resonance frequency of the tag resonators (or close to it), is used as a reader. Thus, during reader operation, the tag chain is mechanically shifted over the transmission line so that the coupling between the line and the functional resonant elements of the tag chain is favored. Logic states that '1' and '0' are determined by the functionality and non-functionality (resonator detuning), respectively, of the resonant elements of the chain. Through near-field coupling, the transmission coefficient of the line is modulated and, as a result, the output signal is modulated in amplitude (AM), which is the identification code contained in the envelope function. As long as the tags are inkjet-printed on ordinary DIN A4 paper, the cost is minimal. Moreover, such tags can be easily programmed and erased, so that identical tags can be fabricated on a large scale (and programmed at a later stage), further reducing the cost of manufacture. The reported prototype tags, with 80 bits of information plus four header bits, demonstrate the potential of this approach, which is of particular interest to secure paper applications.