765 research outputs found
Review on the development of truly portable and in-situ capillary electrophoresis systems
Capillary electrophoresis (CE) is a technique which uses an electric field to separate a mixed sample into its constituents. Portable CE systems enable this powerful analysis technique to be used in the field. Many of the challenges for portable systems are similar to those of autonomous in-situ analysis and therefore portable systems may be considered a stepping stone towards autonomous in-situ analysis. CE is widely used for biological and chemical analysis and example applications include: water quality analysis; drug development and quality control; proteomics and DNA analysis; counter-terrorism (explosive material identification) and corrosion monitoring. The technique is often limited to laboratory use, since it requires large electric fields, sensitive detection systems and fluidic control systems. All of these place restrictions in terms of: size, weight, cost, choice of operating solutions, choice of fabrication materials, electrical power and lifetime. In this review we bring together and critique the work by researchers addressing these issues. We emphasize the importance of a holistic approach for portable and in-situ CE systems and discuss all the aspects of the design. We identify gaps in the literature which require attention for the realization of both truly portable and in-situ CE systems
Development of an autonomous lab-on-a-chip system with ion separation and conductivity detection for river water quality monitoring
This thesis discusses the development of a lab on a chip (LOC) ion separation for river water quality monitoring using a capacitively coupled conductivity detector (C⁴D) with a novel baseline suppression technique.Our first interest was to be able to integrate such a detector in a LOC. Different designs (On-capillary design and on-chip design) have been evaluated for their feasibility and their performances. The most suitable design integrated the electrode close to the channel for an enhanced coupling while having the measurement electronics as close as possible to reduce noise. The final chip design used copper tracks from a printed circuit board (PCB) as electrodes, covered by a thin Polydimethylsiloxane (PDMS) layer to act as electrical insulation. The layer containing the channel was made using casting and bonded to the PCB using oxygen plasma. Flow experiments have been conduced to test this design as a detection cell for capacitively coupled contactless conductivity detection (C⁴D).The baseline signal from the system was reduced using a novel baseline suppression technique. Decrease in the background signal increased the dynamic range of the concentration to be measured before saturation occurs. The sensitivity of the detection system was also improved when using the baseline suppression technique. Use of high excitation voltages has proven to increase the sensitivity leading to an estimated limit of detection of 0.0715 μM for NaCl (0.0041 mg/L).The project also required the production of an autonomous system capable of operating for an extensive period of time without human intervention. Designing such a system involved the investigation of faults which can occur in autonomous system for the in-situ monitoring of water quality. Identification of possible faults (Bubble, pump failure, etc.) and detection methods have been investigated. In-depth details are given on the software and hardware architecture constituting this autonomous system and its controlling software
Lab-on-PCB Devices
Lab-on-PCB devices can be considered an emerging technology. In fact, most of the contributions have been published during the last 5 years. It is mainly focussed on both biomedical and electronic applications. The book includes an interesting guide for using the different layers of the Printed Circuit Boards for developing new devices; guidelines for fabricating PCB-based electrochemical biosensors, and an overview of fluid manipulation devices fabricated using Printed Circuit Boards. In addition, current PCB-based devices are reported, and studies for several aspects of research and development of lab-on-PCB devices are described
A NEW CONDUCTIVE MEMBRANE-BASED MICROFLUIDIC PLATFORM FOR ELECTROKINETIC APPLICATIONS
Micro-total-analysis-system (uTAS), a technology branches from the broader concept, microfluidics, has emerged as a powerful tool for many biological and chemical applications. uTAS typically features sample-to-answer designs, minute sample assumption and short processing time, which are highly desired in point-of-care diagnostics or high-throughput chemical analysis. Despite a large number of microfluidic devices reported with the uTAS concept, most designs were detection and sensitivity focused, ignored the necessary sample preparation steps. In recent years, the increasing demand for chip automation has boosted research efforts on sample preparation.
Electric force serves as one of the most applicable tools among on-chip sample processing techniques due to its portable and easy-integrating nature. To date, research has yielded a large number of designs utilizing electric field as a driving force, also known as electrokinetics, for on-chip sample processing, such as sample purification, enrichment, mixing and sorting. One biggest issue researchers countered using electric field is undesired surface reactions that may cause Faradaic reactions, electrode corrosion, and contaminations. While several microfluidic platforms have been developed to address this issue, there are still growing efforts to create new micro-design that are capable of providing sufficient electric field with improved stability, portability, and robustness.
This thesis seeks to address the electrokinetic-based on-chip sample preparation issue in two aspects, continuity and flow control, which represent two main challenges of on-chip sample preparation: a limited capability to continuously process samples and lacking necessary modules for precise flow control under large extent chip integration. We first developed a new electrokinetic platform with integrated conductive membranes to effectively generate a uniform three-dimensional electric field inside microfluidic channels. The new design also has proved superiorities in avoiding surface reactions, improving portability, and reducing the fabrication cost. We then solved the continuity issue with a free flow electrophoresis device created from the platform. The free flow nature of the device allows for continuous sample throughput while adding electric field perpendicularly offers additional manipulating factors. Utilizing the newly developed free flow electrokinetic chip, we have successfully demonstrated two common on-chip sample processing functions: parallel separation and sample enrichment. On the other hand, the flow control issue is tackled by creating essential on-chip control modules under microfluidic setting. We have designed several microfluidic units with the platform to facilitate on-chip flow regulation, including micro-pumps, a sample injector, a local flow meter and a potential automatic control panel. All the flow control modules can be directly integrated into any soft lithography based sample processing modules without affecting the original designs, which significantly eases the integration difficulty. The ultimate goal of this research shall lead to a microfluidic platform that can perform essential on-chip sample pretreatments in a continuous manner and allows need-based customization. The platform shall be easily integrated with essential power functions and feedback mechanisms for automatic flow control, which offer a possibility to real highly integrated portable devices. Eventually, we can build the real uTAS by combining the platform with our real-time biosensor and turning it into a sample-to-answer uTAS.
In the first chapter of this thesis, a general background correlated to my research work is provided. The introduction includes the uTAS concept and its related technologies, explains the increasing demand for on-chip sample preparation techniques, and discusses current sample process modules using electrokinetic force. It leads to Chapter 2, where I summarize the current electrokinetic-based microfluidic platforms developed to address the surface reaction issue. Then we propose the new platform along with a theoretical model to characterize this design. An extensive comparison between available designs follows to demonstrate the advantages of this new platform, including the comparison specifically focusing on surface reactions. A detailed fabrication process flow is demonstrated in the end, showing how to fabricate this new platform design using one -step photolithography. Then the thesis splits into two parallel blocks, corresponding to the two challenges of on-chip sample preparation. The continuity challenge is addressed on the first block, chapter 3, where free flow electrophoresis device is presented and followed by two demonstrations of on-chip sample pretreatment functions: mixture separation and molecule enrichment. The second block of this thesis discusses the importance of on-chip flow control and the main obstacles that current technologies struggle with. Essential modules for on-chip flow control, such as electro-osmotic pumps, fluid regulation, sample injection techniques, pressure and flow meters, will be demonstrated in chapter 4-6, respectively. In conclusion, I will summarize all my previous research work and how to sketch the big picture of on-chip sample preparation with this platform. The results shall provide guidelines and inspirations for future on-chip sample preparation research
Investigation of the NFC technology for mobile payments and the development of a prototype payment application in the context of marginalized rural areas
Both communication, and the methods and tools of commerce have evolved over time through the invention of new technologies. The latest of these technologies are mobile devices and electronic commerce respectively. The combination of these two technologies has resulted in the creation of electronic commerce which also enables mobile payments. Mobile payments (mpayments) are enabled by many technologies with Near Field Communication (NFC) being the most recent one. NFC is a wireless technology that enables mobile devices in close proximity to exchange data. The mobile device has already been enthusiastically accepted by the customers and they carry it with them wherever they go and this makes it a good device for providing a payment method alternative. This research looks at contactless mobile payment as a payment method. Customers in marginalized rural areas lack a payment alternative to cash hence in this research we are investigating and proposing the use of a NFC enabled mobile payment application for Marginalized Rural Areas. This research extensively evaluates and assesses the potential of using NFC enabled m-payments in Marginalized Rural Areas in South Africa by carrying out an investigation of the technology and its acceptance by customers. The investigation of the technology included implementation of a prototype application which was used to introduce the technology to the consumers. The customer acceptance of the NFC enabled mobile payments was evaluated using the Technology Acceptance model (TAM). The model was modified to suit the context of this study by adding more constructs. This research concluded that Near Field Communication enabled m-payments have great potential to be used and accepted by people in the marginalized rural areas
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