Karl Crowley

Printing conducting polymers

Recent developments in both materials science and printing technologies have led to a rapid expansion in the field of printed conducting polymers. This review provides an overview of the most common printing methods currently in use and the material requirements of each. Examples of printed devices fabricated from a range of conducting polymers are given with an emphasis on the development of sensors.

Fabrication of Polyaniline-Based Gas Sensors Using Piezoelectric Inkjet and Screen Printing for the Detection of Hydrogen Sulfide

This work describes a fully printable polyaniline-copper (II) chloride sensor for the detection of hydrogen sulfide gas. The sensing device is composed of screen printed silver interdigitated electrode (IDE) on a flexible PET substrate with inkjet printed layers of polyaniline and copper (II) chloride. The sensor is employed as a chemiresistor with changes in measured current being correlated with concentration. On exposure to hydrogen sulfide, 2.5 ppmv (parts per million by volume) is clearly detectable with a linear relationship between measured current and concentration over the 10-100 ppmv region. The detection mechanism is discussed with respect to the hydrogen sulfide response, the choice of electrode materials in addition to UV-vis and surface enhanced Raman spectroscopy (SERS) characterization.

Printing polyaniline for sensor applications

In recent years, much research has focused on the development of low-cost, printed electrochemical sensor platforms for environmental monitoring and clinical diagnostics. Much effort in this area has been based on utilising the redox properties of conducting polymers, particularly polyaniline (PANI). In tackling the inherent lack of processability exhibited by these materials, several groups have examined various mass-amenable fabrication approaches to obtain suitable thin films of PANI for sensing applications. Specifically, the approaches investigated over the years include the in situ chemical synthesis of PANI, the use of sulphonated derivatives of PANI and the synthesis of aqueousbased nano-dispersions of PANI. Nano-dispersions have shown a great deal of promise for sensing applications, given that they are inkjet-printable, facilitating the patterning of conducting polymer directly to the substrate. We have shown that inkjet-printed films of PANI can be finely controlled in terms of their two-dimensional pattern, thickness, and conductivity, highlighting the level of precision achievable by inkjet printing. Utilising these nanomaterials as inkjet-printable inks opens novel, facile, and economical possibilities for conducting polymer-printed electronic applications in areas of sensing, but also many other application areas such as energy storage, displays, organic light-emitting diodes. Given that inkjet-printing is a scalable manufacturing technique, it renders possible the large-scale production of devices such as sensors for a range of applications. Several successes have emerged from our work and from the work of others in the area of applying PANI in low-cost sensor applications, which is the focus of this review.

Wholly printed polypyrrole nanoparticle-based biosensors on flexible substrate

Printing has been widely used in the sensor industry for its speed, low cost and production scalability. In this work we present a wholly-printed polypyrrole (PPy) based biosensor produced by inkjet printing bioinks composed of dispersions of PPy nanoparticles and enzymes onto screen-printed carbon electrodes. Two enzymes, horseradish peroxidase (HRP) or glucose oxidase (GoD) were incorporated into the PPy nanoparticle dispersions to impart biosensing functionality and selectivity into the conducting polymer ink. Further functionality was also introduced by deposition of a permselective ethyl cellulose (EC) membrane using inkjet printing. Cyclic voltammetry (CV) and chrono-amperometry were used to characterize the response of the PPy biosensors to H2O2 and glucose. Results demonstrated the possibility of PPy based biosensor fabrication using the rapid and low cost technique of inkjet printing. The detection range of H2O2 was found to be 10 μM-10 mM and for glucose was 1-5 mM.

Direct measurement of ammonia in simulated human breath using an inkjet-printed polyaniline nanoparticle sensor

A sensor fabricated from the inkjet-printed deposition of polyaniline nanoparticles onto a screen-printed silver interdigitated electrode was developed for the detection of ammonia in simulated human breath samples. Impedance analysis showed that exposure to ammonia gas could be measured at 962 Hz at which changes in resistance dominate due to the deprotonation of the polymer film. Sensors required minimal calibration and demonstrated excellent intra-electrode baseline drift (≤1.67%). Gases typically present in breath did not interfere with the sensor. Temperature and humidity were shown to have characteristic impedimetric and temporal effects on the sensor that could be distinguished from the response to ammonia. While impedance responses to ammonia could be detected from a single simulated breath, quantification was improved after the cumulative measurement of multiple breaths. The measurement of ammonia after 16 simulated breaths was linear in the range of 40-2175 ppbv (27-1514 μg m(-3)) (r(2)=0.9963) with a theoretical limit of detection of 6.2 ppbv (4.1 μg m(-3)) (SN(-1)=3).

Simultaneous Web-based real-time temperature monitoring using multiple wireless sensor networks

We outline a system that allows simultaneous temperature monitoring on two or more fishing vessels using multiple wireless sensor networks. The distribution of wireless temperature data loggers across a boat with an associated base station results in the fishing vessel being in effect an individual wireless sensor network. The existence of this wireless sensor network allows for real-time temperature monitoring with the temperature information being accessed over the Internet. Previously, Web-based real-time temperature monitoring of fish catches has used single sensor networks to monitor temperature, so a user could only monitor the temperature sensors of a single vessel. The system we outline allows for multiple sensor networks to be integrated and for a user to monitor temperature across two or more of these networks. Furthermore the system uses SMS to send warnings and to monitor recent temperature data. The system is built around a Web server and bespoke wireless data loggers operating over a GSM network

A gas-phase colorimetric sensor for the detection of amine spoilage products in packaged fish

In this work, the design and application of a colorimetric amine sensor is detailed. The sensor consists of a pH indicator dye immobilised within a rugged, gas-permeable polymer film. The visual transition can be monitored quantitatively using a custom-built LED probe, or qualitatively with the human eye (i.e. using a colour code). Incorporation of several indicator dyes allows the monitoring of pH over an extended range and the sensor also has many potential applications in gas phase analysis (6 ppm LOD for ammonia). In this case, the sensor has been tailored to monitor TVB-N (total volatile basic nitrogen) spoilage products in the headspace of packaged fish. As the fish spoils, a colour change results as the TVB-N compounds shift the pH to higher values. This provides a non-invasive and simple method of rapidly detecting spoilage of produce inside sealed packaging. In trials to date, the sensor response has been found to mirror the progress of microbial spoilage

Wireless temperature logging technology for the fishing industry

A system for autonomous temperature logging of fish catches is described. The system is completely wireless and is comprised of a number of loggers, in individual fish boxes, and a base station, assigned to a particular trawler. The temperature of the fish is monitored by the loggers, which contain a thermistor and RF transmitter circuitry. The data is sent at fixed intervals (usually 5 minutes) to the base station. Through a GSM modem, the base station communicates the collected data to the shore where a server uploads the temperature-time information to a database. The database and controlling software are completely Web-based and can be accessed by an Internet-enabled PC, laptop or PDA. This allows remote initiation and control of the system, in addition to querying of the database. To date, successful trials have been conducted for salmon, mackerel and whelk fishing off the Irish coast.

A sensor probe for the continuous in situ monitoring of ammonia leakage in secondary refrigerant systems

Ammonia is becoming more widely used in refrigeration systems due to the phasing out of CFCs and HCFCs. However, ammonia is a toxic gas and its leakage from refrigeration systems can lead to human exposure and contamination of refrigerated food stuffs. There is a lack of devices capable of the direct and continuous monitoring of leakage of ammonia into secondary refrigerant systems. Here we demonstrate an ammonia measurement probe for continuous contact monitoring of secondary refrigerants. The probe was based on an ammonia-sensitive film of inkjet printed polyaniline nanoparticles deposited onto an interdigitated electrode array and enclosed behind a polytetrafluoroethylene membrane. When operated impedimetrically, the probe was capable of the detection of ammonia across the industrially relevant range of 0 to 100 ppm from +4 to −15 °C in water and brine. Operation of the probe as a simple threshold alarm without the requirement for temperature monitoring or calibration is illustrated.

Fabrication of chemical sensors using inkjet printing and application to gas detection

This work describes the fabrication of gas sensors using inkjet printing. Sensors were constructed by building up a film of sensing material, such as polyaniline, from aqueous nanoparticulate dispersions. These films were printed over patterned silver interdigitated array designs for the purposes of conductimetric analysis. Unlike screen printing or lithography, inkjet printing does not require stencils or masks, therefore allowing rapid design and prototyping. For this study, polyaniline and modified polyaniline sensors were inkjet printed and assessed for the purposes of gas sensing applications, specifically hydrogen sulfide monitoring.