Comparison of printing techniques for the fabrication of flexible carbon nanotube-based ammonia chemiresistive gas sensors

Even though a plethora of printing technologies are currently available and their potential for the fabrication of low-cost and flexible sensors has been widely investigated, systematically based, and statistically sustained comparative studies are missing in the literature. In this work, we compare screen, inkjet, and dispense printing for the fabrication of carbon nanotube (CNT)-based ammonia (NH3) chemiresistive flexible gas sensors for the first time. Moreover, we report the first CNT-based gas sensor fabricated via Voltera printer. The devices were made of a thin layer of spray-coated CNTs and printed silver-based interdigitated electrodes. To draw a thoughtful comparison the same sensor layout, materials, and fabrication flow were used. The device morphological features were acquired through microscopic, atomic force microscope, and 3D images; additionally, the response to NH3 as well as the printing process characteristics for each technique was analyzed. From 300 μm nominal spacing between lines, we obtained a decrease of 25%, 13%, and 5% on the printed spacings with dispense, screen, and inkjet printing, respectively. At 100 ppm of NH3, a maximum response of 33%, 31%, and 27% with the dispense-, inkjet-, and screen-printed sensors were found, respectively. Statistical differences were observed between the mean values on the NH3 response of dispense- compared to the inkjet- and screen-printed sensors, which in effect showed the highest response in the Tukey test. This demonstrated that the fabrication technique employed can induce a different response mainly driven by the printed outcomes. Following a holistic approach that includes the sensor response, the application, the market perspective, and the process versatility, we suggest screen printing as the most suitable method for CNT-based NH3 gas sensor fabrication. 1. Introduction In the last decade, several manufacturing technologies have been extensively exploited to fabricate gas sensors, including chemical vapor deposition [1], physical vapor deposition [2], micromachining [3], self-assembly [4], spray coating [5, 6], and printing [7, 8]. Among all, the latter is the most commonly utilized technology for developing miniaturized, portable, and low-cost sensors [9]. Indeed, over theEuropean Regional Development Fund (ERDF) Program (Project codes EFRE/FESR 1068-Senslab and EFRE/FESR 1127-STEX)Free University of Bozen-Bolzan

Cost-Effective PEDOT:PSS Temperature Sensors Inkjetted on a Bendable Substrate by a Consumer Printer

In this work, we report on a fabrication protocol to produce fully inkjet-printed temperature sensors on a bendable polyethylene terephthalate (PET) substrate. The sensing layer is made of polymer-based Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) ink that is electrically contacted by an underlying interdigitated electrode (IDE) structure based on a silver nanoparticle (AgNP) ink. Both inks are available commercially, and no further ink processing is needed to print them using a cost-effective consumer printer with standard cartridges. The fabricated sensor modules are tested for different IDE dimensions and post-deposition treatments of the AgNP film for their response to a temperature range of 20 to 70 °C and moisture range of 20 to 90% RH (relative humidity). Attributed to the higher initial resistance, sensor modules with a larger electrode spacing of 200 µm show a higher thermal sensitivity that is increased by a factor of 1.8 to 2.2 when compared to sensor modules with a 150 µm-spacing. In all cases, the sensors exhibit high linearity towards temperature and a response comparable to state of the art.This research was funded by the European Union through the fellowship H2020-MSCA-IF-2017 794885-SELFSENS and the TUM Graduate Schoo

A Facile and Efficient Protocol for Preparing Residual-Free Single-Walled Carbon Nanotube Films for Stable Sensing Applications

In this article, we report on an efficient post-treatment protocol for the manufacturing of pristine single-walled carbon nanotube (SWCNT) films. To produce an ink for the deposition, the SWCNTs are dispersed in an aqueous solution with the aid of a carboxymethyl cellulose (CMC) derivative as the dispersing agent. On the basis of this SWCNT-ink, ultra-thin and uniform films are then fabricated by spray-deposition using a commercial and fully automated robot. By means of X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), we show that the CMC matrix covering the CNTs can be fully removed by an immersion treatment in HNO3 followed by thermal annealing at a moderate temperature of 100 ºC, in the ambient air. We propose that the presented protocols for the ink preparation and the post-deposition treatments can in future serve as a facile and efficient platform for the fabrication of high-quality and residual-free SWCNT films. The purity of SWCNT films is of particular importance for sensing applications, where residual-induced doping and dedoping processes distort the contributions from the sensing specimen. To study the usability of the presented films for practical applications, gas sensors are fabricated and characterized with the CNT-films as the sensing material, screen printed silver-based films for the interdigitated electrode (IDE) structure, and polyimide as a flexible and robust substrate. The sensors show a high and stable response of 11% to an ammonia (NH3) test gas, at a concentration of 10 ppm.The authors thank the Deutsche Forschungsgemeinschaft (DFG) and the Natural Sciences and Engineering Research Council (NSERC) for financial support of the Alberta/Technische Universität München Graduate School for Functional Hybrid Materials ATUMS (IRTG2022, NSERC CREATE), as well as the TUM Graduate School, the Nanosystems Initiative Munich (NIM), and the TUM International Graduate School of Science and Engineering (IGSSE)

Screen-Printed Chipless Wireless Temperature Sensor

A chipless wireless sensor for temperature monitoring is described in this work. The sensor is fabricated by screen printing of an RLC circuit on a flexible substrate. The sensing element is a resistive carbon paste with positive temperature coefficient placed in a small area in the interconnection between the inductor and the capacitor. This sensing layer modifies the resonance frequency of the circuit when the temperature varies. We also show the influence of the sensor sensitivity with respect to the reading distance

treNch: Ultra-Low Power Wireless Communication Protocol for IoT and Energy Harvesting

Although the number of Internet of Things devices increases every year, efforts to decrease hardware energy demands and to improve efficiencies of the energy-harvesting stages have reached an ultra-low power level. However, no current standard of wireless communication protocol (WCP) can fully address those scenarios. Our focus in this paper is to introduce treNch, a novel WCP implementing the cross-layer principle to use the power input for adapting its operation in a dynamic manner that goes from pure best-effort to nearly real time. Together with the energy-management algorithm, it operates with asynchronous transmissions, synchronous and optional receptions, short frame sizes and a light architecture that gives control to the nodes. These features make treNch an optimal option for wireless sensor networks with ultra-low power demands and severe energy fluctuations. We demonstrate through a comparison with different modes of Bluetooth Low Energy (BLE) a decrease of the power consumption in 1 to 2 orders of magnitude for different scenarios at equal quality of service. Moreover, we propose some security optimizations, such as shorter over-the-air counters, to reduce the packet overhead without decreasing the security level. Finally, we discuss other features aside of the energy needs, such as latency, reliability or topology, brought again against BLE.ECSEL Joint Undertaking through CONNECT project 737434Federal Ministry of Education & Research (BMBF)European Union's Horizon 2020 research and innovation programSpanish Ministry of Education, Culture and Sport (MECD)/FEDER-EU FPU18/01376BBVA FoundationUniversity of Granad

Bioprecipitation of Calcium Carbonate Crystals by Bacteria Isolated from Saline Environments Grown in Culture Media Amended with Seawater and Real Brine

The precipitation of calcium carbonate and calcium sulphate by isolated bacteria from seawater and real brine obtained in a desalination plant growth in culture media containing seawater and brine as mineral sources has been studied. However, only bioprecipitation was detected when the bacteria were grown in media with added organic matter. Biomineralization process started rapidly, crystal formation taking place in the beginning a few days after inoculation of media; roughly 90% of total cultivated bacteria showed. Six major colonies with carbonate precipitation capacity dominated bacterial community structure cultivated in heterotrophic platable bacteria medium. Taxonomic identification of these six strains through partial 16S rRNA gene sequences showed their affiliation with Gram-positive Bacillus and Virgibacillus genera. These strains were able to form calcium carbonate minerals, which precipitated as calcite and aragonite crystals and showed bacterial fingerprints or bacteria calcification. Also, carbonic anhydrase activity was observed in three of these isolated bacteria. The results of this research suggest that microbiota isolated from sea water and brine is capable of precipitation of carbonate biominerals, which can occur in situ with mediation of organic matter concentrations. Moreover, calcium carbonate precipitation ability of this microbiota could be of importance in bioremediation of CO2 and calcium in certain environments.This investigation was funded by the EC FP7 CO2SolStock research consortium

Optimization of a Handwriting Method by an Automated Ink Pen for Cost-Effective and Sustainable Sensors

In this work, we present a do-it-yourself (DIY) approach for the environmental-friendly fabrication of printed electronic devices and sensors. The setup consists only of an automated handwriting robot and pens filled with silver conductive inks. Here, we thoroughly studied the fabrication technique and different optimized parameters. The best-achieved results were 300 mΩ/sq as sheet resistance with a printing resolution of 200 µm. The optimized parameters were used to manufacture fully functional electronics devices: a capacitive sensor and a RFID tag, essential for the remote reading of the measurements. This technique for printed electronics represents an alternative for fast-prototyping and ultra-low-cost fabrication because of both the cheap equipment required and the minimal waste of materials, which is especially interesting for the development of cost-effective sensors.TUM Graduate School and by the European Commission through the fellowship H2020-MSCA-IF-2017-794885-SELFSEN

Screen Printable Electrochemical Capacitors on Flexible Substrates

This work presents a novel approach for the fabrication of Electrochemical Capacitors (ECs) based on the screen-printing of a commercial carbon-based conductive ink on flexible substrates. This technique enables the fast and cost-effective production of ECs with high flexibility and outstanding performance over bending states and voltage cycling, as demonstrated by means of cyclic voltammetry and galvanometric charge-discharge measurements. Despite the fact that the specific areal capacitances achieved are lower than the ones obtained using other carbon-based materials (~22 μF/cm2), the results show that, as soon as new screen-printable carbon-based pastes become available, this fabrication method will enable the mass production of ECs that can be attached to any surface as a conformal patch, as it is being required by a large number of the emerging technological applications.This work has been partially supported by the Spanish Ministry of Education, Culture and Sport (MECD) and the European Union through the pre-doctoral grant FPU16/01451, and its mobility program, the project TEC2017-89955-P and fellowship H2020-MSCA-IF-2017794885-SELFSENS

Over-Stretching Tolerant Conductors on Rubber Films by Inkjet-Printing Silver Nanoparticles for Wearables

The necessity to place sensors far away from the processing unit in smart clothes or artificial skins for robots may require conductive wirings on stretchable materials at very low-cost. In this work, we present an easy method to produce wires using only commercially available materials. A consumer grade inkjet printer was used to print a wire of silver nanoparticles with a sheet resistance below 1 W/sq. on a non-pre-strained sheet of elastic silicone. This wire was stretched more than 10,000 times and was still conductive afterwards. The viscoelastic behavior of the substrate results in a temporarily increased resistance that decreases to almost the original value. After over-stretching, the wire is conductive within less than a second. We analyze the swelling of the silicone due to the ink’s solvent and the nanoparticle film on top by microscope and SEM images. Finally, a 60 mm long stretchable conductor was integrated onto wearables, and showed that it can bear strains of up to 300% and recover to a conductivity that allows the operation of an assembled LED assembled at only 1.8 V. These self-healing wires can serve as wiring and binary strain or pressure sensors in sportswear, compression underwear, and in robotic applications.This work has been partially supported the TUM Graduate School (TUM GS), and the European Union through the fellowship H2020-MSCA-IF-2017 794885-SELFSENS. Additionally, this work was supported by the German Research Foundation (DFG) and the Technical University of Munich within the Open Access Publishing Funding Programme

Cost-effective printed electrodes based on emerging materials applied to biosignal acquisition

In this paper flexible printed electrodes applicable to wearable electronics are presented. Using innovative materials as Laser Induced Graphene (LIG) and printed electronics, three type of electrodes based in LIG, silver chloride and carbon inks have been compared during the acquisition of bipotentials as electrocardiogram, electromyogram and electrooculogram. For this last one, a completely new framework for acquisition have been developed. This framework is based in a printed patch which integers 6 electrodes for the EOG acquisitions and an ad-hoc signal processing to detect the direction and amplitude of the eye movement. The performance of the developed electrodes have been compared with commercial ones using the characteristics parameters of each signal as comparative variables. The results obtained for the flexible electrodes have shown a similar performance than the commercial electrodes with an improvement in the comfort of the user.Spanish Ministry of Education, Culture and Sport (MECD)/FEDER-EU TEC2017-89955-P FPU16/01451 FPU18/01376BBVA FoundationUniversity of Granad