Ehsan Danesh

Development of a New Generation of Ammonia Sensors on Printed Polymeric Hotplates

Conducting polyaniline-based chemiresistors on printed polymeric micro-hotplates were developed, showing sensitive and selective detection of ammonia vapor in air. The devices consist of a fully inkjet-printed silver heater and interdigitated electrodes on a polyethylene naphthalate substrate, separated by a thin dielectric film. The integrated heater allowed operation at elevated temperatures, enhancing the ammonia sensing performance. The printed sensor designs were optimized over two different generations, to improve the thermal performance through careful design of the shape and dimension of the heater element. A vapor-phase deposition polymerization technique was adapted to produce polyaniline sensing layers doped with poly(4-styrenesulfonic acid). The resulting sensor had better thermal stability and sensing performance when compared with conventional polyaniline-based sensors, and this was attributed to the polymeric dopant used in this study. Improved long-term stability of the sensors was achieved by electrodeposition of gold on the silver electrodes. Response to sub-parts-per-million concentrations of ammonia even under humid conditions was observed.

Cyanoethyl cellulose-based nanocomposite dielectric for low-voltage, solution-processed organic field-effect transistors (OFETs)

Low voltage organic field-effect transistors (OFETs) using solution-processed cyanoethyl cellulose (CEC) and CEC-based nanocomposites as the gate dielectric are demonstrated. Barium strontium titanate (BST) nanoparticles are homogeneously dispersed in CEC to form the high-k (18.0 ± 0.2 at 1 kHz) nanocomposite insulator layer. The optimised p-channel DPPTTT OFETs with BST-CEC nanocomposite as the gate dielectric operate with minimal hysteresis, display field-effect mobilities in excess of 1 cm2 V−1 s−1 at 3 V, possess low subthreshold swings (132 ± 8 mV dec−1), and have on/off ratios greater than 103. Addition of a 40–50 nm layer of cross-linked poly(vinyl phenol) (PVP) on the surface of the nanocomposite layer significantly decreases the gate leakage current (<10−7 A cm−2 at ±3 V) and the threshold voltage (< −0.7 V) enabling operation of the OFETs at 1.5 V. The presented bilayer BST-CEC/PVP dielectrics are a promising alternative for the fabrication of low voltage, solution-processed OFETs that are suitable for use in low power, portable electronics.

Smart RFID Label with a Printed Multisensor Platform for Environmental Monitoring

This work reports on the design, fabrication and characterization of an inkjet-printed multisensing platform on flexible polymeric substrates integrated into a printed semi-passive high frequency radio frequency identification (HF RFID) smart label. The printed platform was integrated after fabrication to the main RFID carrier, which contained an NFC RFID chip, a microprocessor, a readout frontend and a screen-printed circuitry and antenna. The multisensing platform has channels for capacitive vapor detection (i.e. humidity), two channels for resistive-based vapor detection (i.e. ammonia) with heating capability, and one resistive channel for temperature detection (RTD). A modular approach was employed where the sensing platform was integrated to the base RFID label carrier using foil-to-foil integration techniques compatible with large area fabrication. Besides wireless communication, the semi-passive label possesses data logging and the possibility of measuring all the sensors simultaneously through a direct readout circuitry. In addition to individual sensor characterization, the full functionality of the smart label was successfully demonstrated by measuring different temperature, humidity and ammonia levels.

Fully solution processed low voltage OFET platform for vapour sensing applications

Herein, we report the development, fabrication and evaluation of a fully solution processed low-voltage operation organic Field-effect transistor (OFET) sensor platform. The sensors performance was evaluated against ammonia as an example of environmental and health care monitoring applications. The sensor was able to detect ammonia at concentrations as low as 600 ppb under high humidity conditions (RH = 80%). The platform can easily be upscaled to a sensor array comprising multiple OSCs, thus the range of analytes of interest to environmental and point of care applications reaches far beyond ammonia.

Flexible Ammonia Sensor Based on Polyaniline/Carbon Black Composites Operating at Elevated Temperatures

• For the EB the absorption band at ca.635 nm is relate to the n-π* transition (quinoid form structure) → undoped/ half oxidized PANI structure. • For ES (either with SSA or SPhA) the absorption at ca. 435 nm is due to the presence of localized semiquinone population or the polaron absorption. The long free tail extended to near IR region may be attributed to highly delocalized free electron state of polyaniline doped with these dopants.