Inkjet-printing supports environmentally friendly manufacturing of printed electronics and enables rapid prototyping with low material waste. In this work, inkjet-printed conductive tracks on ethyl 2-cyanoacrylate (superglue) is compared to tracks printed on paper. This work will provide solutions for disposable biosensing, where the biocompatibility of versatile superglue is important. The emphasis throughout the work is on developing a biocompatible device. Dog-bone structures with different line widths were printed on paper and superglue, providing comparative results obtained from dimensional and electrical characterisation. On average the tracks printed on superglue have a 2.6 times higher resistivity than those printed on paper, but are acceptable for printed electronics networks. When considering a lumped component ac model, the 500 μm tracks on superglue have a series inductance of 2.6 nH, while the 4-point Kelvin probe characterisation of the 100 μm and 250 μm tracks printed on superglue show a capacitive equivalent impedance with capacitance values of 2.8 μF and 2.6 μF respectively. The 100 μm, 250 μm and 500 μm tracks printed on paper have inductance values of 1.20 nH, 11.30 nH and 14.8 nH, respectively. All printed tracks have linear frequency operational ranges larger than 1 MHz. A biocompatibility test was performed with Escherichia coli (E. coli) O157:H7. The silver nanoparticle ink proved to be antibacterial, while paper, superglue and gold nanoparticle ink was biocompatible. These results provide information assisting the design process for bio applications that require conformal and multi-substrate printing.
This paper presents the development of design software for inkjet-printed resistor structure layout, which con- tributes to rapid prototyping of good quality printed electronics circuits. The synthesis software was implemented using the Java SE Development Kit 8 and provides a GUI front end and automated design of resistive structures for ease of use. Several layout configurations synthesized for inkjet-printed nanosilver resistors were validated over a range of 1 Ω to 200 Ω. In doing so, Harima NPS-JL silver nanoparticle ink was characterized for sheet resistance and TCR. The software was able to synthesize resistive structures with a worst-case error of 19%, and thus, has the potential to produce practical structures for use in real world applications, such as a printed heating element for a thermal petri dish incubator.
A Metal-Insulator-Metal (MIM) capacitor was inkjet-printed, using a dielectric ink (Ink-Epo-XP from MicroResist) based on SU-8 photo-resist, as well as silver nanoparticle ink (Harima NPS-J) for conductive features, which was integrated into a microsystem power supply. It was discovered that printing MIM capacitors on photo-paper had the most promising results in terms of acceptable capacitance density and flexibility, when compared to transparency and glass substrates. A core aspect considered in this project was the discovery of the workflows best suited to print MIM capacitors, which included using oxygen plasma treatment and the printing of various layers. Capacitors with values ranging between 10 and 50 pF were integrated into AC-DC and DC-DC converters. The AC-DC converter had a power output of up to 8.75 W with an output voltage of 5 V, whereas the DC-DC converters had outputs of up to 200 mW at voltages ranging between 1.8-3.3 V. The converters realised reached efficiencies of 80.77 % (AC-DC) and 70-92 % (DC-DC) respectively.
This paper presents a printed paper-based origami electrochemical sensor for the detection of heavy metals in water. Heavy metal contamination in water has significant health risks and environmental complications. The detection is typically performed in a laboratory with lengthy result turnaround times. Paper-based detection provides an ideal platform on which to develop solutions to address these challenges, particularly for under-resourced settings, as it is inexpensive, disposable, and can be deployed at the point-of-need to provide rapid results for environmental and disease control. The paper-based origami device was successfully fabricated using wax printing techniques to print the hydrophobic barriers and screen printing techniques to print the three-electrode electrochemical sensor on chromatography paper. An origami design enables enhanced fluidic control to be achieved, as the porous paper structure facilitates flow, and filters out all potential debris in the sample before reaching the sensor. Vertical as well as horizontal fluidic flow is realized using the folding origami design, allowing for better filtering of debris. The results demonstrate the filtering of debris from dirty water and the detection of parts per billion levels of lead and cadmium ions in buffer solution on a single two-dimensional electrochemical sensor printed on chromatography paper. The detection results of lead and cadmium ions on chromatography paper were compared to commercially available screen-printed ceramic electrochemical sensors. The proposed paper-based origami electrochemical sensor device with fluidic handling capabilities demonstrates a simple, low-cost, disposable paper device suitable for the detection of heavy metals in water samples.
The internet of things (IoT) has resulted in accelerated development of intelligent and connected devices. Important modules include those for monitoring of environmental parameters and sensors for health diagnostic applications. Flexible, low-cost implementations are desirable towards free-form, customizable and disposable solutions for sensing and wireless connectivity. This work presents a flexible, low-cost, printed wireless temperature logger, utilizing a sensing radio frequency identification (RFID) integrated circuit (IC). The temperature logger devices were screen printed and assembled on low-cost, flexible vinyl adhesive substrates for ease of mounting on to a variety of surfaces and objects, and were tested with both coin cell batteries and screen printed primary batteries designed and manufactured in-house. The SL900A RFID IC (AMS, Austria) has internal features to monitor temperature and battery voltage. The chip was set up to log the battery voltage and the temperature over different time frames in controlled temperature environments to test the reliability of the temperature readouts. In addition, logging of the battery voltage levels enabled the performance of the printed batteries to be assessed. The results showed accurate readings over 4 days for both coin cell and printed batteries without limiting the data logging capabilities. The printed wireless temperature logger shows promise towards all-printed, low-cost solutions for environmental monitoring using an integrated and connected device approach with on-board power.
This paper presents the design of a low-complexity, linear and sub-pF CMOS capacitance-frequency converter for reading out a capacitive bacterial bio/sensors with the endeavour of creating a universal bio/sensor readout module. Therefore the priority design objectives are a high resolution as well as an extensive dynamic range. The circuit is based on a method which outputs a digital frequency signal directly from a differential capacitance by the accumulation of charges produced by repetitive charge integration and charge preservation1. A prototype has been designed for manufacture in the 0.35 μm, 3.3V ams CMOS technology.
At a 1MHz clock speed, the most pertinent results obtained for the designed converter are: (i) power consumption of 1.37mW; (ii) a resolution of at least 5 fF for sensitive capacitive transduction; and (iii) an input dynamic range of at least 43.5 dB from a measurable capacitance value range of 5 – 750 fF (iv) and a Pearson’s coefficient of linearity of 0.99.
KEYWORDS: Bacteria, Silver, Biosensing, Temperature metrology, Manufacturing, Sensors, Resistance, Temperature sensors, Finite element methods, Convection
The presence of Escherichia coli (E. coli ) is a commonly used indicator micro-organism to determine whether water is safe for human consumption.1 This paper discusses the design of a micro-incubator that can be applied to concentrate bacteria prior to environmental water quality screening tests. High sensitivity and rapid test time is essential and there is a great need for these tests to be implemented on-site without the use of a laboratory infrastructure. In the light of these requirements, a mobile micro-incubator was designed, manufactured and characterised. A polydimethylsiloxane (PDMS) receptacle has been designed to house the 1-5 ml cell culture sample.2 A nano-silver printed electronics micro-heater has been designed to incubate the bacterial sample, with an array of temperature sensors implemented to accurately measure the sample temperature at various locations in the cell culture well. The micro-incubator limits the incubation temperature range to 37±3 °C in order to ensure near optimal growth of the bacteria at all times.3 The incubation time is adjustable between 30 minutes and 9 hours with a maximum rise time of 15 minutes to reach the set-point temperature. The surface area of the printed nano silver heating element is 500 mm2. Electrical and COMSOL Multiphysics simulations are included in order to give insight on micro-incubator temperature control. The design and characterization of this micro-incubator allows for further research in biosensing applications.
We present an ultra-high frequency radio frequency identification based wireless communication set-up for paper-based
point-of-care diagnostic applications, based on a sensing radio frequency identification chip. Paper provides a low-cost,
disposable platform for ease of fluidic handling without bulky instrumentation, and is thus ideally suited for point-ofcare
applications; however, result communication – a crucial aspect for healthcare to be implemented effectively – is still
lacking. Printing of radio frequency identification antennas and electronic circuitry for sensing on paper are presented,
with read out of the results using a radio frequency identification reader illustrated, demonstrating the feasibility of
developing integrated, all-printed solutions for point-of-care diagnosis in resource-limited settings.
Electrochemical biosensing is used to detect specific analytes in fluids, such as bacterial and chemical contaminants. A common implementation of an electrochemical readout is a potentiostat, which usually includes potentiometric, amperometric, and impedimetric detection. Recently several researchers have developed small, low-cost, single-chip silicon-based potentiostats. With the advances in heterogeneous integration technology, low-power potentiostats can be implemented on paper and similar low cost substrates. This paper deals with the design of a low-power paper-based amperometric front-end for a low-cost and rapid detection environment. In amperometric detection a voltage signal is provided to a sensor system, while a small current value generated by an electrochemical redox reaction in the system is measured. In order to measure low current values, the noise of the circuit must be minimized, which is accomplished with a pre-amplification front-end stage, typically designed around an operational amplifier core. An appropriate circuit design for a low-power and low-cost amperometric front-end is identified, taking the heterogeneous integration of various components into account. The operational amplifier core is on a bare custom CMOS chip, which will be integrated onto the paper substrate alongside commercial off-the-shelf electronic components.
A general-purpose low-power two-stage CMOS amplifier circuit is designed and simulated for the ams 350 nm 5 V process. After the layout design and verification, the IC was submitted for a multi-project wafer manufacturing run. The simulated results are a bandwidth of 2.4 MHz, a common-mode rejection ratio of 70.04 dB, and power dissipation of 0.154 mW, which are comparable with the analytical values.
This paper describes the development and optimisation of a paper-based E. coli impedimetric biosensor for water quality monitoring. Impedimetric biosensing is advantageous because it is a highly sensitive, label-free, real-time method for the detection of biological species. An impedimetric biosensor measures the change in impedance caused by specific capture of a target on the sensor surface. Each biosensor consists of a pair of photo paper-based inkjet printed electrodes. An impedance analyser was used to measure the impedance at frequencies ranging from 1 kHz to 1 MHz at 1V.
The parameters that were investigated to achieve enhanced sensor performance were buffer type, antibody attachment method, measurement frequency, electrode layout, and conductive material. A 0.04M PBS (phosphate buffered saline) solution achieves better results compared to a less conductive 0.04M PB (potassium phosphate dibasic) solution. The direct adsorption of anti-E. coli antibodies onto the sensor surface yielded better results than attaching the sensor to a lateral flow test. The resistive component had a greater impact on the detected impedance, therefore an optimal frequency of 1 MHz was identified. Geometrical electrode designs that maximise the resistive change between the electrodes were utilised. Both lower cost silver and bio-compatible gold ink were validated as electrode materials. The impedance change generated by the selective capture of E. coli K-12, ranging in concentration from 103 to 107 colony forming units per millilitre (cfu/ml), showed a detection limit of 105 cfu/ml.
We present a method for the development of paper-based electrochemical sensors for detection of heavy metals in water samples. Contaminated water leads to serious health problems and environmental issues. Paper is ideally suited for point-of-care testing, as it is low cost, disposable, and multi-functional. Initial sensor designs were manufactured on paper substrates using combinations of inkjet printing and screen printing technologies using silver and carbon inks. Bismuth onion-like carbon nanoparticle ink was manufactured and used as the active material of the sensor for both commercial and paper-based sensors, which were compared using standard electrochemical analysis techniques. The results highlight the potential of paper-based sensors to be used effectively for rapid water quality monitoring at the point-of-need.
Lab-on-a-chip devices are often applied to point-of-care diagnostic solutions as they are low-cost, compact, disposable, and require only small sample volumes. For such devices, various reagents are required for sample preparation and analysis and, for an integrated solution to be realized, on-chip reagent storage and automated introduction are required. This work describes the implementation and characterization of effective liquid reagent storage and release mechanisms utilizing blister pouches applied to various point-of-care diagnostic device applications. The manufacturing aspects as well as performance parameters are evaluated.
We present a visualization pipeline from sample to answer for point-of-care blood cell counting applications. Effective and low-cost point-of-care medical diagnostic tests provide developing countries and rural communities with accessible healthcare solutions [1], and can be particularly beneficial for blood cell count tests, which are often the starting point in the process of diagnosing a patient [2]. The initial focus of this work is on total white and red blood cell counts, using a microfluidic cartridge [3] for sample processing. Analysis of the processed samples has been implemented by means of two main optical visualization systems developed in-house: 1) a fluidic operation analysis system using high speed video data to determine volumes, mixing efficiency and flow rates, and 2) a microscopy analysis system to investigate homogeneity and concentration of blood cells. Fluidic parameters were derived from the optical flow [4] as well as color-based segmentation of the different fluids using a hue-saturation-value (HSV) color space. Cell count estimates were obtained using automated microscopy analysis and were compared to a widely accepted manual method for cell counting using a hemocytometer [5]. The results using the first iteration microfluidic device [3] showed that the most simple – and thus low-cost – approach for microfluidic component implementation was not adequate as compared to techniques based on manual cell counting principles. An improved microfluidic design has been developed to incorporate enhanced mixing and metering components, which together with this work provides the foundation on which to successfully implement automated, rapid and low-cost blood cell counting tests.
There is an inherent trade-off between cost and operational integrity of microfluidic components, especially when intended for use in point-of-care devices. We present an analysis system developed to characterise microfluidic components for performing blood cell counting, enabling the balance between function and cost to be established quantitatively. Microfluidic components for sample and reagent introduction, mixing and dispensing of fluids were investigated. A simple inlet port plugging mechanism is used to introduce and dispense a sample of blood, while a reagent is released into the microfluidic system through compression and bursting of a blister pack. Mixing and dispensing of the sample and reagent are facilitated via air actuation. For these microfluidic components to be implemented successfully, a number of aspects need to be characterised for development of an integrated point-of-care device design. The functional components were measured using a microfluidic component analysis system established in-house. Experiments were carried out to determine: 1. the force and speed requirements for sample inlet port plugging and blister pack compression and release using two linear actuators and load cells for plugging the inlet port, compressing the blister pack, and subsequently measuring the resulting forces exerted, 2. the accuracy and repeatability of total volumes of sample and reagent dispensed, and 3. the degree of mixing and dispensing uniformity of the sample and reagent for cell counting analysis. A programmable syringe pump was used for air actuation to facilitate mixing and dispensing of the sample and reagent. Two high speed cameras formed part of the analysis system and allowed for visualisation of the fluidic operations within the microfluidic device. Additional quantitative measures such as microscopy were also used to assess mixing and dilution accuracy, as well as uniformity of fluid dispensing - all of which are important requirements towards the successful implementation of a blood cell counting system.
SU-8/Clay nanocomposite is considered as a candidate material for microcantilever sensor fabrication. Organically modified montmorillonite clay nanoparticles are dispersed in the universally used negative photoresist polymer SU-8, for a low cost material, which is also biocompatible. If varying the clay loading of the composite material yields a variation of the Young's modulus, the tailored material stiffness presents an opportunity for fabrication of microcantilevers with tunable sensor sensitivity. With this microcantilever application perspective, mechanical and thermal properties of the material were investigated. SU-8/Clay nanocomposite samples were prepared with clay loadings from 1wt% - 10wt%. Tensile test results show a general trend of increase in composite modulus with an increase in the clay loading up to 7wt%, followed by a small drop at 10wt%. The composite material indeed yields moderate variation of the Young's modulus. It was also found that the thermal degradation peak of the material occurred at 300°C, which is beyond the operating temperature of typical microcantilever sensor applications. The fabrication of a custom designed microcantilever array chip with the SU-8/Clay nanocomposite material was achieved in a class 100 cleanroom, using spin-coating and photolithography microfabrication techniques. The optimization of the process for fabricating microcantilever with the SU-8/Clay nanocomposite material is discussed in this paper. The results of this research are promising for cheaper mass production of low cost disposable, yet sensitive, microcantilever sensor elements, including biosensor applications.
Multiplexed or parallelised droplet microfluidic systems allow for increased throughput in the production of emulsions and microparticles, while maintaining a small footprint and utilising minimal ancillary equipment. The current paper demonstrates the design and fabrication of a multiplexed microfluidic system for producing biocatalytic microspheres. The microfluidic system consists of an array of 10 parallel microfluidic circuits, for simultaneous operation to demonstrate increased production throughput. The flow distribution was achieved using a principle of reservoirs supplying individual microfluidic circuits. The microfluidic devices were fabricated in poly (dimethylsiloxane) (PDMS) using soft lithography techniques. The consistency of the flow distribution was determined by measuring the size variations of the microspheres produced. The coefficient of variation of the particles was determined to be 9%, an indication of consistent particle formation and good flow distribution between the 10 microfluidic circuits.
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