Search

An analysis on the viability of implementing non-flow based capacitive biosensing for bulk counting of whole cancer cells is presented. A mathematical model is implemented based on established research to test the validity of the hypothesis that cells are considered to act like parallel electric connections. A finite element analysis model is also presented to investigate the effect of electrode geometry and cell position on the measured capacitance. The electrical interaction between cells is found not to be strictly parallel and in fact dependent on a host of uncontrollable parameters. Bulk sensing of multiple cells is found to be impractical for a single electrode setup due to the unpredictability of cell location and cell interactions. An array-based implementation is proposed, which allows for the use of current models and data of single-cell analyses to be used.

The analysis of contact resistance in bottom-gate top-contact thin-film transistors (TFTs) based on nanoparticulate ZnO and a high-k nanocomposite as semiconductor and gate dielectric, respectively, shows that nickel can be used as an alternative to aluminum contacts. Furthermore, an analysis of the morphology of the gate structures and the influence of the work function of the gate metal on the transistor properties is carried out. For this purpose, gate electrodes were made of aluminum (4.28 eV) and gold (5.1 eV). It can be demonstrated that increasing the work function influences the flat-band voltage and thus the turn-on voltage. This effect can also be observed in bottom-gate bottom-contact devices with self-aligned drain/source electrodes.

The need for effective point-of-need health and environmental diagnostics in low and middle income countries (LMICs) is more crucial than ever. This work explores emerging criteria and technologies to address the limitations of current point-of-need solutions. Local developments in South Africa towards this goal are highlighted, utilizing additive manufacturing technologies which combine paper-based diagnostic and printed electronic platforms. Establishment of a pipeline, from undergraduate engineering students and laboratory infrastructure to industry partners using a decentralized manufacturing approach are also discussed as a map for developing novel, low-cost solutions for improving the quality of life of those who need it most.

Thin-film transistors (TFTs) enable low-cost integration of electronic circuits. Due to the low thermal load during manufacturing, flexible substrates can be used, making TFTs suitable for flexible electronic applications such as RFID labels or diagnostic sensors. To achieve mass applications, an increase in the performance of TFTs is required. In this context, the transit frequency f T is an important indicator. This frequency is influenced not only by the charge carrier mobility but also by the overlap of the gate electrode with the drain/source electrodes and by the channel length [1]. For realistic mobilities of about 10 cm2/ Vs and low operating voltages (V D ≤ 10 V), channel lengths in the submicrometer range are required for transit frequencies in the megahertz region [2]. In this work, we report on an integration routine for TFT fabrication in the submicron range by combining a dry etching process for structuring the gate electrode with a self-alignment process for patterning the drain/source electrodes. The self-alignment also minimizes the overlap between the gate and the drain/source electrodes, thus reducing the parasitic capacitances.

According to the UNESCO World Water Development Report 2019 [1], one half of all people with insufficient access to drinking water are located in African states. In the sub-Saharan region the percentage of those with access to clean drinking water is at 24% only. The exploitation of new water sources by means of laboratory water quality analysis may lead to costs of about 30$ each [2]. In view of the above, a low-cost sensor system has been developed that intends to provide a feedback on the general quality of a water probe and gives a statement on the possibility of dissolved chemicals in the probe.

Flexible electronics requires the integration of thin-film transistors (TFTs) at much lower temperatures than traditional Si technology. Here we present an integration routine for complementary inverter structures on a flexible polyethylene terephthalate (PET) substrate, which provides a high degree of freedom in the choice of the individual contact metals for the p-and n-type TFTs. It is therefore suitable for organic, inorganic or hybrid semiconductor systems. The developed integration process enables two different metallization layers to be structured into contact electrodes (drain and source) for thin film transistors on a common flexible substrate. This enables the adaptation of the work function of metals and semiconductors, and thus the performance of the individual TFTs can be optimized. The TFTs are integrated in bottom-gate bottom-contact setup.

The work presented details micro and nano technologies for point-of-need health and environmental diagnostics in resource-limited settings, specifically in Southern Africa. The challenges faced in these settings have limited the effectiveness of point-of-need diagnostic solutions. By combining the growing fields of paper-based diagnostics and printed electronics, the extensive possibilities of functional printing can be utilized to develop novel, low-cost solutions for improving the quality of life of those who need it most. Examples of the research progress made in South Africa are presented, with a map for the way forward, encompassing the different technologies, skills and manufacturing processes required.

This work details manufacturing processes developed to integrate an unpackaged silicon die onto a paper substrate, as part of constructing a hybrid inkjet-printed paper-based circuit. This integration between rigid components and flexible substrates is beneficial in low-cost applications and capitalises on the advantages of both the well-established integrated circuit technology and the emerging paper-based electronics platforms. A superglue incline at the chip edge formed a ramp for printing the silver interconnects between the paper-based circuit and the chip pads. Two printing protocols are compared, the first a single layer using 5 μm drop spacing, and the second using a 35 μm drop spacing for three layers. An unpackaged RFID tag die is successfully integrated and is presented as proof of concept.

Impedance spectroscopy is a widely used electrochemical technique with a wide variety of applications. Many of these applications benefit from the additional accessibility provided by low-cost impedance devices. With this in mind, a low-cost impedance device was designed for a high performance-to-cost ratio. The performance of this analyzer was validated against a high-performance DropSens µStat-i 400s potentiostat by performing an application-based experiment. Nitrate detection provides a relevant experiment because of the importance of maintaining precise nitrate concentrations to mitigate the impact of nitrate fluctuations on the environment. Dissolved nitrate samples of different concentrations, in the range 3–1000 mg/L, were confirmed colorimetrically and measured with both instruments. A calibration curve of the real impedance matched a sigmoidal transfer, with a linear region for concentrations below 10 mg/L. The device under investigation exhibited an average magnitude error of 1.28% and an average phase error of 0.96∘ relative to the high-performance standard, which validates the performance of the low-cost device. A cost analysis is presented that highlights some of the complexities of cost comparisons.

This paper presents inductor design via ink-jet printing techniques for planar and multi-planar inductors while considering flexible substrates. These inductor designs can be adapted for use in high frequency filtering and power transfer in microelectronics. For these inductor designs, silver nanoparticle ink (Harima MPS-JL) was ink-jetted and cured on photo paper using a Dimatix DMP-2850 printer in order to construct spiral as well as meander printed inductors. The spiral inductor designs constructed consider both planar and multi-planar formats for both square and circular geometries whereas the meander inductor designs are strictly planar. The operational bandwidth of these inductors were limited to 10 MHz in order to compare design outputs such as quality factor, inductance and impedance. Subsequent testing, in order to demonstrate both high frequency filtering as well as power transfer, using auxiliary circuits was done.

Water being used for any purpose needs to adhere to a certain quality standard. Performing tests to ensure water quality can be done in an analytical laboratory with high precision using a wide range of techniques and equipment. There is a growing need, however, for low-cost point-of-need (PON) solutions that would be able to serve a larger portion of earth’s population. One of the techniques, Impedance Spectroscopy (IS), measures the impedance of a water sample across a wide range of frequencies in order to analyse some frequency dependent properties of a sample. The problem addressed in this project is to develop an inexpensive, PON, system that can perform Impedance Spectroscopy on water samples. The impedance spectroscopy system is being developed in CMOS using the 0.35um ams AG process and will produce an impedance spectrum with frequencies ranging from 1 Hz to 10 MHz. The system interfaces with water samples through a standard three-point electrode, with voltage signals being maintained between the reference and working electrode. The analog front end for measurement as well as the digital control circuitry is included in the CMOS design.

Inkjet-printed capacitive circuits on different substrates will be investigated. This work will contribute towards rapidly prototyping electronic systems for smart ubiquitous biosensors. These biosensors require sensitive and robust signal readout with low power consumption and wireless connectivity while also being inexpensive. Capacitors were printed on different substrates, including glass and overhead projector film, to characterize an inkjet-printed dielectric. A Fujifilm Dimatix DMP2831 was used to print different functional inks, including Harima silver nanoparticle ink and InkEpo-XP ink. The silver nanoparticle ink was used to print the conductive features of the capacitors while the InkEpo-XP was used as the dielectric material. Different test patterns were printed with silver ink on the dielectric material; these patterns were used to establish a printing protocol for successful printing of silver on the dielectric material. Different test patterns were also printed with dielectric ink on silver to create a printing protocol for successfully printing dielectric on silver. Metal-insulator-metal capacitors were successfully inkjet printed on glass and overhead projector film with silver and dielectric inks. The metal-insulator-metal capacitors were used to characterize the dielectric material at different frequencies. The circuit modelling of the capacitors is discussed, and validated against experimental results. A design procedure is presented for reliably printing capacitive networks with feature dimensions between 1 mm and 2 mm on glass and overhead projector film.

This paper covers the design of a complementary metal oxide semiconductor (CMOS) pixel readout circuit with a built-in frequency conversion feature. The pixel contains a CMOS photo sensor along with all signal-to-frequency conversion circuitry. An 8×8 array of these pixels is also designed. Current imaging arrays often use analog-to-digital conversion (ADC) and digital signal processing (DSP) techniques that are off-chip1. The frequency modulation technique investigated in this paper is preferred over other ADC techniques due to its smaller size, and the possibility of a higher dynamic range. Careful considerations are made regarding the size of the components of the pixel, as various characteristics of CMOS devices are limited by decreasing the scale of the components2. The methodology used was the CMOS design cycle for integrated circuit design. All components of the pixel were designed from first principles to meet necessary requirements of a small pixel size (30×30 μm2) and an output resolution greater than that of an 8-bit ADC. For the photodetector, an n+-p+/p-substrate diode was designed with a parasitic capacitance of 3 fF. The analog front-end stage was designed around a Schmitt trigger circuit. The photo current is integrated on an integration capacitor of 200 fF, which is reset when the Schmitt trigger output voltage exceeds a preset threshold. The circuit schematic and layout were designed using Cadence Virtuoso and the process used was the AMS CMOS 350 nm process using a power supply of 5V. The simulation results were confirmed to comply with specifications, and the layout passed all verification checks. The dynamic range achieved is 58.828 dB per pixel, with the output frequencies ranging from 12.341kHz to 10.783 MHz. It is also confirmed that the output frequency has a linear relationship to the photocurrent generated by the photodiode.

In this paper, a new approach to energy harvesting and data transmission optimization in a heterogeneous-based multi-class and multiple resource wireless transmission wireless sensor network system that focus on monitoring water and its quality is presented. Currently, energy is a scarce resource in wireless sensor networks due to the limited energy budget of batteries, which are typically employed for powering sensors. Once the available energy of a particular sensor node battery is depleted, such sensor node becomes inactive in a network. As a consequence, such node may not be able to participate in the transmission of the application signal in the uplink stage of the network, resulting in a lack of ability to communicate vital signals in a timely manner. Energy scarcity has been a long standing problem in wireless sensor network applications. To address this problem, energy harvesting from intended radiofrequency power source is considered in this work. However, wirelessly powered wireless sensor network systems are confronted by unfairness in resource allocation problem, as well as interference problem in multiple energy resource transmissions. These problems adversely impact the performance of the system in the context of the harvested energy by the sensor nodes, sensors information transmission rates, and the overall system throughput rate. These problems are tackled in this paper by formulating a sum-throughput maximization problem to reduce system energy consumption and enhance the system overall throughput rate. The throughput optimization problem is formulated as a non-convex function. Through the exploitation of the problem structure, it is converted to a convex function. The mathematical models of the optimization problem are validated through numerical simulations. The simulation results reveal that the proposed wireless powered sensor network system outperforms an existing wireless powered sensor network system, by comparison of the numerical simulations of this work to the numerical simulations of the existing WPSN system, regardless of the distances of the sensor nodes to the IPS and the base station. Also, the newly proposed method performs efficiently using parameters that include path-loss exponent impact, performance comparison of systems, convergence based on iteration, comparison based on unequal network distances to the BS, transmission power impact on the attainable throughput and on fraction of energy consumed on information transmissions, and influence of different number of nodes in the network classes.

Avalanche electroluminescence from silicon pn junctions has been known for many years. However, the internal quantum efficiencies of these devices are quite low due to the indirect band gap nature of the semiconductor material. In this study we have used reach-through biasing and SOI (silicon-on-insulator) thin film structures to improve the internal power efficiency and the external light extraction efficiency. Both continuous silicon thin film pn junctions and parallel nanowire pn junctions were manufactured using a custom SOI technology. The pn junctions are operated in the reach-through mode of operation, thus increasing the average electric field within the fully depleted region. Experimental results of the emission spectrum indicate that the most dominant photon generating mechanism is due to intraband hot carrier relaxation processes. It was found that the SOI nanowire light source external power efficiency is at least an order of magnitude better than the comparable bulk CMOS (Complementary Metal Oxide Semiconductor) light source.

This study presents novel approaches to the allocation of resources in Internet-of-Things sensor network (IoTSN) systems applied to water-quality monitoring for optimal and more sustainable utilization of resources. To tackle the long-standing energy scarcity issue that currently plagues sensor network (SN) systems, energy harvesting is explored and exploited to maximize its untapped potential to develop asuccessive wireless power sensor network (WPSN) system embedded with a scheduling algorithm, and operate as a non-orthogonal multiple access (NOMA) system. Similarly, quality of service parameters are crucial design considerations for network efficiency,and energy efficiency (EE) is considered here. Consequently, an EE optimization problem is formulated for the successiveWPSN system and solved by exploiting the problem structure and through a meta-heuristic algorithm. The new system is validated through the numerical simulation results presented in this work by thoroughly analyzing, evaluating and comparing the proposed meta-heuristic based WPSN system with the baseline state-of-the-art WPSN systems that combined a meta-heuristic algorithm, two additional meta-heuristic algorithms including genetic algorithm (GA) and ant-colony optimization (ACO) algorithm as well as a non-meta-heuristic algorithm – specifically an iterative based Dinkelbach algorithm.The experimental outcomes show that the proposed system significantly outperforms the contemporary WPSN systems in terms of EE performance gains.

This work presents a new approach to the maximization of energy and throughput in a wireless sensor network (WSN), with the intention of applying the approach to water-quality monitoring. Water-quality monitoring using WSN technology has become an interesting research area. Energy scarcity is a critical issue that plagues the widespread deployment of WSN systems. Different power supplies, harvesting energy from sustainable sources, have been explored. However, when energy-efficient models are not put in place, energy harvesting based WSN systems may experience an unstable energy supply, resulting in an interruption in communication, and low system throughput. To alleviate these problems, this paper presents the joint maximization of the energy harvested by sensor nodes and their information-transmission rate using a sum-throughput technique. A wireless information and power transfer (WIPT) method is considered by harvesting energy from dedicated radio frequency sources. Due to the doubly near–far condition that confronts WIPT systems, a new WIPT system is proposed to improve the fairness of resource utilization in the network. Numerical simulation results are presented to validate the mathematical formulations for the optimization problem, which maximize the energy harvested and the overall throughput rate. Defining the performance metrics of achievable throughput and fairness in resource sharing, the proposed WIPT system outperforms an existing state-of-the-art WIPT system, with the comparison based on numerical simulations of both systems. The improved energy efficiency of the proposed WIPT system contributes to addressing the problem of energy scarcity.

Hot carrier electroluminescence in two junction devices under punch through conditions manufactured in silicon on insulator nanowires are investigated. Of interest is the spectral content of the light emission, as well as the external power efficiency and the light extraction efficiency. An order of magnitude improvement in external power efficiency was achieved relative to a bulk silicon p-n junction in avalanche.

This work investigates the properties of conductive circuits inkjet-printed onto the polycarbonate discs used in CD-based centrifugal microfluidics, contributing towards rapidly prototyped electronic systems in smart ubiquitous biosensors, which require sensitive and robust signal readout at low power and cost, and with wireless connectivity. A protocol for inkjet-printing electronic networks on CD substrates is developed. The circuit modeling of conductive tracks is discussed, and validated against experimental results. A design procedure is presented for reliably printing conductive networks with feature dimensions between 150 μm and 2 mm on CDs, and yielding electronic circuits operating with a bandwidth of 1 MHz.

The work presented details the development of a low-cost potentiostat, with the aim of creating an ink-jet printed hybrid paper-based low-cost sensing system for rapid water quality monitoring. Potentiostats exhibit high sensitivities and can be used for a variety of applications. In this application, they use electrochemical techniques to detect heavy metals via stripping analysis. The potentiostat front-end, consisting of an LMP91000 sensing chip, was designed and manufactured on a printed circuit board (PCB) and compared to a laboratory-based potentiostat using cyclic voltammetry performed using an 80 sl sample of 5 mM ferri-ferrocyanide dropped onto a commercial screen-printed electrode. The results obtained from the PCB potentiostat are comparable to those obtained using the development board and the laboratory-based potentiostat. The results highlight the functionality of a low-cost point-of-need potentiostat that can be used for environmental monitoring as well as the feasibility of transferring the design to a paper substrate.

Applications for diagnostic and environmental point-of-need require processes and building blocks to add smart features to disposable biosensors on low-cost substrates. A novel method for producing such biosensors is printing electronics using additive technologies. This work contributes to the toolbox of processes, materials and components for printed electronics manufacturing - as well as rapid prototyping - of circuits. Printing protocols were developed to facilitate successful inkjet printing of nanosilver ink (Harima NPS-JL) onto different microsystem substrates using a functional printer (Dimatix DMP-3281). Photo paper is a standard inkjet substrate, which were compared with glass, polycarbonate (PC), plastic projector transparency foil, and polydimethylsiloxane (PDMS). Comparison attributes include physical and electrical properties. The layout design comprised dogbone elements of 8 mm length, and widths varying between 100 μm and 2 mm. All printed features were thermally cured for 1 hour at 120 °C. The physical characteristics were measured with a laser scanning microscope (Zeiss LSM-5) to determine the width, thickness and surface roughness of the printed features. An LCR meter (GW-Instek 8110) was used to measure the printed structures’ electrical characteristics (resistance, capacitance and inductance). A lumped element model and layout design rules were extracted to assist in standardized design procedures. The model incorporates prediction of the bandwidth attainable with these structures. The layer thickness on all substrates is larger than the 1 μm on photo paper, and varies between 1.6 μm (PC) and 7 μm (PDMS). The spreading for PDMS is similar to photo paper, but since for the other substrates it is between 5 (glass) and 10 (PC) times larger than for photo paper, the layout design rules require large spacing, leading to larger area networks. Electrical probing on the PDMS is not consistent and results are inconclusive. For the other substrates, the comparative dogbone resistance (100 μm width) is significantly larger than the 2 Ω standard, varying from 12.6 Ω (PC) to 19.3 Ω (glass). The bandwidth relative to photo paper is smaller by a factor of between 6 (PC) and 9.5 (glass).

Research on affordable point-of-care health diagnostics is rapidly advancing1. Colorimetric biosensor applications are typically qualitative, but recently the focus has been shifted to quantitative measurements2,3. Although numerous qualitative point-of-care (POC) health diagnostic devices are available, the challenge exists of developing a quantitative colorimetric array reader system that complies with the ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, Deliverable to end-users) principles of the World Health Organization4. This paper presents a battery powered 8-bit tonal resolution colorimetric sensor circuit for paper microfluidic assays using low cost photo-detection circuitry and a low-power LED light source. A colorimetric 3×3-pixel array reader was developed for rural environments where resources and personnel are limited. The device sports an ultralow-power E-ink paper display. The colorimetric device includes integrated GPS functionality and EEPROM memory to log measurements with geo-tags for possible analysis of regional trends. The device competes with colour intensity measurement techniques using smartphone cameras, but proves to be a cheaper solution, compensating for the typical performance variations between cameras of different brands of smartphones. Inexpensive methods for quantifying bacterial assays have been shown using desktop scanners, which are not portable, and cameras, which suffer severely from changes in ambient light in different environments. Promising colorimetric detection results have been demonstrated using devices such as video cameras5, digital colour analysers6, flatbed scanners7 or custom portable readers8. The major drawback of most of these methods is the need for specialized instrumentation and for image analysis on a computer.

Cooling and ventilation systems play an important role in human occupied spaces. However, cooling using reversible air conditioners systems pollutes the environment and consumes a significant amount of energy. With global warming that experiences our environment, the large consumption of electrical energy and the operating instructions for reversible air conditioners, there is a need to find alternatives to those cooling systems. Hence this research project aims to investigate an air storage system, a microsystem reversible ventilation system using natural atmospheric air (renewable energy) for cooling at low consumption of energy. For the variation of the temperature range of comfort due to thermal heat produces by occupants, equipment and environment, an optimal transient automatic regulation of air flow as to be design in order to maintain the temperature of comfort in occupied spaces during peak hours.

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.

This paper investigates the avalanche electroluminescence characteristics of pn junctions formed in silicon nanowires fabricated in a silicon-on-insula*tor (SOI) technology. Since carriers are confined to the nanowires, it is possible to study the effect of electric field strength on device performance while the current density and carrier concentrations are kept constant. This is achieved by varying the nanowire length while keeping the bias current constant, eventually driving the pn junction into the reach-through bias condition. It is observed that photon emission for photon energies higher than 1.2 eV increases when the nanowire length is reduced, while photon emission with energies less than 1.2 eV decreases. The higher electric field in the nanowire at shorter nanowire lengths enhances the high-energy photon emission and attenuates the low energy photon emission.

Low-cost and non-invasive diabetes diagnosis is increasingly important [1], and this paper presents a handheld readout system for chemiresistive gas sensors in a breath acetone diagnostic application. The sensor contains reference and detection devices, used for the detection of gas concentration. Fabrication is by dropcasting a metaloxide nanowire solution onto gold interdigitated electrodes, which had been manufactured on silicon. The resulting layer is a wide bandgap n-type semiconductor material sensitive to acetone, producing a change in resistance between the electrode terminals [2]. Chemiresistive sensors typically require temperatures of 300-500 °C, while variation of sensing temperature is also employed for selective gas detection. The nano-structured functional material requires low temperatures due to large surface area, but heating is still required for acceptable recovery kinetics. Furthermore, UV illumination improves the sensor recovery [3], and is implemented in this system. Sensor resistances range from 100 Ω to 50 MΩ, while the sensor response time require a sampling frequency of 10Hz. Sensor resistance depends on temperature, humidity, and barometric pressure. The GE CC2A23 temperature sensor is used over a range of -10°C to 60°C, the Honeywell HIH5031 humidity sensor operates up to 85% over this temperature range, and the LPS331AP barometric pressure sensor measures up to 1.25 bar. Honeywell AWM43300V air flow sensors monitor the flow rate up to 1000 sccm. An LCD screen displays all the sensor data, as well as real time date and time, while all measurements are also logged in CSV-format. The system operates from a rechargeable battery.

Copyright: 2017 SPIE. Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, kindly consult the publisher's website.

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.

This article reports the modification of optical properties of biodegradable/biocompatible polylactide (PLA) using organically modified montmorillonite (OMMT) for microcantilever applications. PLA/OMMT composite films with various OMMT loadings (3, 5 and 7 wt%) were prepared using solvent casting. The surface morphology of the PLA/OMMT composites was examined using scanning electron and atomic force microscopes. The morphological results indicated that the surface roughness increases as a function of the clay loading. The optical properties of the PLA/OMMT composites were studied using variable angle spectroscopic ellipsometry (VASE) and ultra-violet (UV-Vis) spectroscopy. VASE revealed that the refractive index and extinction coefficient (n and k) positively correlated with the thickness of the film. UV-Vis spectroscopy also demonstrated that the absorption of light by PLA/OMMT composite films positively correlated with the clay content in the visible range of the electromagnetic spectrum. To enhance the reflectivity, PLA/OMMT films were coated with a gold layer.

Current centralised healthcare models pose many challenges, particularly for developing countries such as South Africa, where travel and time costs make it difficult for patients to seek healthcare, even when urgently needed. To address this issue, point-of-care (PoC) tests, which are performed at or near the site of clinical care, have gained popularity and are actively being developed. Microfluidic systems, in which small volumes of fluids can be processed, provide an ideal platform on which to develop PoC diagnostic solutions. Specifically, the emerging field of paper-based microfluidics, with advantages such as low-cost, disposability and minimal external equipment requirements, provides unique opportunities for addressing healthcare issues in developing countries. This work explores the field of paper-based microfluidics, with step-by-step instructions on the design, manufacture and testing processes to realise paper-based devices towards diagnostic applications. Paper-based microfluidic and electronic components are presented, as well as the integration of these components to provide smart paper-based devices. This serves as an educational tool, enabling both beginners and experts in the field to fast-track development of unique paper-based solutions towards PoC diagnostics, with emphasis on the South African context, where both the need for and impact of these solutions are great.