Abstracts of lectures
An overview of global printed electronics activities (Raghu Das)
Over 1500 companies are developing printed electronics, with most see it becoming a hundred-billion dollar market rapidly. In this presentation you will learn about the breadth of what printed electronics is, major global activities, the market potential and applications, and challenges to commercialization.
Is it time to completely re-think how we do chemical sensing? (Prof. Dermot Diamond)
Chemical sensors and biosensors are devices that provide information about binding events happening at the interface between a sensitive film/membrane and a sample phase. The function of the sensitive film/membrane is to ensure that the binding at this interface is as selective as possible and hence the film/membrane usually contains entrapped or covalently bound sites (e.g. ligands, enzymes, antibodies) to control binding activity at the interface. The binding events are further coupled with a transduction mechanism of some kind; such as a change in the colour or fluorescence of the film/membrane, or a shift in electrochemical potential.
Clearly, the materials used in to generate the signal must be ‘active’ in that they must interact with the sample, and binding processes must occur that lead to signal transduction for them to be of any analytical use. However, it is self-evident that these sensitive interfaces will change over time, for example due non-specific binding in real samples that can lead to surface poisoning, or leaching of active components into the sample phase. Consequently, the response characteristics of chemical sensors and biosensors tend to change over time, and there tends to be a gradual decrease in sensitivity, loss of selectivity and drifting of the baseline signal. These effects are well-known to those experienced in using these devices, and in practice, they may be overcome by regular calibration, until the device deterioration reaches some limiting level.
Currently, there is very significant interest in the deployment of sensor networks, and many important applications require the involvement of chemical sensors and biosensors. However, for this to happen in large-scale (ultimately 'internet-scale'), there needs to be a revolution in the way chemical sensors/biosensors are employed, as conventional calibration is inappropriate for large-scale deployments due to the cost of ownership (particularly maintenance) of these rather complex devices.
Furthermore, there is a need to re-think how chemical sensors are fabricated. In this respect, a move towards all-polymeric devices is desirable to enable very low-cost mass production of chemical sensors. Using these in a collaborative manner rather than solitary stand-alone sensors could be beneficial, in terms of cross-validating responses and achieving a higher degree of certainty in decision-making. These concepts have important implications for future chemo/bio-sensor deployments in environmental monitoring, personal health monitoring and threat detection.
Single channel and dual channel field-effect chemical sensors (Prof. Ananth Dodabalapur)
Chemical and biosensors based on field-effect devices with organic and polymer semiconductors have been demonstrated by many groups. Such sensors, which work for a variety of vapor phase and aqueous analytes, can be formed cheaply by printing methods. The selectivity can be enhanced by adding receptor molecules to the semiconductor film. We have recently reported a hybid four-terminal field effect sensor with two coupled channels: one silicon and one organic/polymer. This dual channel sensor works in many modes and is more sensitive than either an equivalent organic transistor sensor or a CHEMFET. Detection limits of about 50 ppb for alcohols have been demonstrated. We have recently realized an all-organic/polymer dual channel device. Yet another device that has been realized and tested as a sensor uses a high k organic based self-assembled gate insulator.
Inkjet printed films of organic materials for chemical sensing (Dr. Mohammed Mabrook)
Chemical sensing technology now encompasses a variety of applications, ranging from electrochemical analysis, through biomedical measurements, to pollution monitoring and industrial control. There is already a demand for simple, low-cost devices to detect small concentrations of airborne chemicals. There is also a need for single-use sensors for medical analysis and for situations in which cross-contamination is a problem. Chemiresistors, based on conductive polymers are particularly attractive as these compounds can be modified chemically to exhibit a high sensitivity to a range of gases and vapours, and have the potential for room temperature operation. Moreover, the materials can be processed easily by techniques such as electrochemical deposition, self-assembly, spin-coating or inkjet printing. The latter technique is attracting considerable attention for ‘plastic’ electronics applications such as organic electroluminescent displays, sensors and field effect transistors. Inkjet printing offers particular advantages over other methods for forming thin films: patterning capability; reduction in waste products; high speed and low cost fabrication; room temperature deposition; and printing onto large area and flexible substrates. For chemical sensing applications, the more ‘open’ morphology of inkjet-printed films (i.e. a series of connected droplets) may allow rapid diffusion of the vapour molecules into and out of the film, leading to fast response and recovery times. Arrays of sensing elements can also be printed from different ‘inks’. In our previous work, conductive polymers have been used as the basis for a sensor for organic vapours at room temperature. Ppoly(3,4-ethylene dioxythiophene) doped with polystyrene sulfonated acid (PEDOT-PSS), polypyrrole and carbon nanotubes were used as the organic inks. The electrical resistance of the sensor was monitored as it was exposed to atmospheres containing alcohol. For the polypyrrole chemiresistors, a significant increase in conductivity was observed on the exposure of the films to the vapours of simple alcohols. The value of the fractional resistance change, ΔR/R, of the films increased linearly with increasing concentrations of alcohols. Thin films of PEDOT-PSS chemiresistors exposed to alcohols exhibited a sharp, non-reversible increase in film resistance (a ‘chemical fuse’) which was attributed to a change in morphology of the PEDOT-PSS layer. An intended application for these inkjet-printed devices is in disposable handheld instruments to monitor the presence of organic vapours above a threshold level.
Organic light-emitting device arrays in structurally integrated chemical and biological sensors (Dr. Ruth Shinar)
This presentation will describe the development, advantages, challenges, and potential of an emerging, compact photoluminescence-based sensing platform for chemical and biological analytes. In this platform, the excitation source is an array of organic light-emitting device (OLED) pixels that is structurally integrated with a sensing component. Steps towards advanced integration with additionally an array of thin-film-based photodetectors will also be described. The performance of the OLED-based sensing platform in monitoring single analytes and multiple analyte mixtures will be shown for, e.g., gas-phase and dissolved oxygen, glucose, lactate, ethanol, hydrazine, and anthrax lethal factor.
Printed chemical and biosensors: technology, design, and challenges (Prof. Vivek Subramanian)
Printed organic transistors have received significant attention for use as active chemical and biosensing transducers in recent years. Here, I review our work on development of a range of printed electronic chemical sensors and DNA sensors based on printed transistors. By using functionalized organic semiconductors, we are able to implement a range of chemical sensing and DNA sensing functionality. Based on a review of our sensor characteristics, I review system level concerns with implementation of organic transistor-based sensors and identify remaining challenges and potential solutions.
Gating via an electrolyte: devices, materials and processing for low-voltage operating and fast switching electronic systems on flexible foils (Prof. Magnus Berggren)
Along the electrolyte-organic semiconductor interface very high electric fields can be generated thanks to the creation of an electric double layer. First, this can offer gating in the field-effect mode to achieve fast-switching transistors operating at voltages below 1 V. Second, in the electrochemical mode transistors can be made including receptors, defining an operation principle suitable for robust and simple sensor transistors. Electrolyte-gated transistors are relatively more robust and more easily manufactured as compared to their dielectric-gated equivalences. We report novel electrolyte-gated transistors and their associated manufacturing techniques to make complete systems on flexible carriers.
Roll-to-roll manufacturing of low cost diagnostics: examples of optical and microfluidic structures (Dr. Markku Känsäkoski)
Traditionally, the primary function of printing has been the delivery of data and information for visual inspection and further interpretation by humans or machines. The advantage of printing is that it enables cost efficient mass manufacturing of electronics and other functionalities on large and flexible substrates like plastic, paper and fabrics. New printable functional materials, print production processes and reading mechanisms are expanding the role and function of printing toward printed intelligence. This is the opportunity gap between traditional paper, packaging and printing industry products and ICT/electronics industry products and can be realised for example as disposable sensors, simple ‘electronic’ components and circuits, large area functional paper like intelligent products, smart packages, etc.Ageing population in Europe will increasingly burden the health care system, e.g. chronic diseases are becoming more and more common and are influencing the quality of life of rapidly increasing number of people. New solutions for low cost and distributed biomolecular recognition measurements are required to reduce the number of costly laboratory tests, hospital controls and idle visits to general practices.Recent developments of hot embossed microfluidics and optics, has made it possible to fabricate functional components by roll-to-roll techniques. In this presentation, we show our current achievements for manufacturing low cost immunosensors for point-of-care and home care applications through examples of microfluidic and optical structures.
Organic transistors for stable aqueous sensors (Mark Roberts and Prof. Zhenan Bao)
The development of low-cost, reliable sensors will rely upon systems capable of converting an analyte binding event to an easily read electrical signal. Organic thin-film transistors (OTFTs) are ideal for inexpensive, single-use chemical or biological sensors due to their compatibility with flexible, large-area substrates, simple processing, and highly tunable active layer materials. We have fabricated OTFTs with a cross-linked polymer gate dielectric, which display stable operation under aqueous conditions over more than 104 electrical cycles. OTFT sensors were demonstrated in aqueous solutions with concentrations as low as parts per billion for trinitrobenzene, methylphosphonic acid, cysteine and glucose. This is the first demonstration of reliable OTFT operation in aqueous media, hence opening new possibilities of chemical and biological sensing with OTFTs.
Printed Sensors (Franz Padinger)
An introduction to printed sensors will be given with a presentation of the Semiconductor 2.0 platform technology used at NANOIDENT. Some applications in biometrics & life science will be highlighted.
Vapour sensing using amorphous organic semiconductors (Prof. Michael Turner)
This contribution discusses the use of amorphous semiconducting polymers as active materials for OFET-based sensors. The lower charge carrier mobility of these materials, compared to crystalline organic semiconductors, is not a significant drawback for their use in sensor applications, as we have been able to demonstrate the comprehensive and accurate characterization of these OFETs using only low cost, standard electronic components even for carrier mobilities as low as » 10-5 cm2V-1 s-1. We have shown that OFETs based on amorphous PTA derivatives can serve as highly sensitive detectors for the common environmental pollutant NO2. In particular, PTA-OMe responds to 10 ppb NO2.