Fabrication of integrated microfluidic devices for point-of-collection analysis of biological and environmental samples

Lab-on-chip systems, also known as micro total analytical systems (˜í¬¿TASs), were introduced in late 80's, and are widely used in analytical chemistry for biological and environmental analysis. Sample preparation is often the most complex andcritical step in analysis ‚Äö- required to eliminate the large number of components that may interfere with the target and to enrich the trace amounts to detectable levels. While sample pretreatment is often conducted off-line, which is usually very time-consuming and labour-intensive, it also has a significant risk of analyte loss, degradation of the sample, or the introductionof contaminants. Benefiting from the portability, compactness, high levels of integrating and automation, integrated microfluidic systems are providing an alternative for point-of-collection (POC) biological and environmental analysis without sample pretreament, mitigating the risks caused by off-line sample pretreatment. This thesis focuses on different integrated microfluidic systems using various manufacturing methods for direct biological and environmental analysis. Chapter 1 offers an overview of the POC analysis of biological and environmental samples. It starts with POCT analysis of drugs in body fluids with microfluidic systems, both therapeutic and illicit drugs detection in various matrixes including blood, urine, saliva etc. are discussed. This is followed by a brief overview of POCT analysis of environmental samples, focusing on the use of microfluidic paper-based analytical devices(˜í¬¿PADs), Polydimethylsiloxane (PDMS) and 3D printed chips are also mentioned, highlighting the many advantages of 3D printing for microfluidic fabrication such as: cost-effectiveness, less time-consuming and labour-intensive, and especially suitable for complex and integrated microfluidic manufacturing. Chapter 2 is a comprehensive review of 3D printed integrated microfluidic devices for chemical applications. Different 3D printing technologies including fused deposition modeling (FDM), Polyjet, Stereolithography (SLA) and others are demonstrated for integrated device manufacturing. In particular how 3D printing can integrate various functionalities (detection, sensor, membrane, etc.) into microfluidic devices using multi mateiral printing or post-print with assembly. In Chapter 3, an integrated microfluidic device was fabricated by sandwiching two nanoporous polycarbonate track etched (PCTE) membranes with differently sized nanopores between PDMS slabs containing embedded microchannels. This device is developed to seamlessly integrate sample preparation, and electrophoretic separation of proteins. The application was for the sample-in/answer-out quantification of albumin in human urine within 2.5 min. Results showed an improvement in sensitivity of 500 fold compared to a normal pinched injection using fluorescence detection. While effective, this approach was time-consuming and labour-intensive due to the lithography fabrication process for PDMS chips, raising the question of whether there are easier, and better approaches to fabricate these types of devices. In Chapter 4, a microfluidic device containing an integrated porous membrane and embedded liquid reagent was made by multi material 3D printing (3DP) with a single step in 30 min. The body of the device was printed in transparent acrylonitrile butadiene styrene (ABS), and contained a 400 ˜í¬¿m wide membrane printed from a commercially available composite filament. Liquid reagents were integrated by briefly pausing the printing before resuming sealing the device. The devices were evaluated by the determination of nitrate in soil slurry containing zinc particles for the reduction of nitrate to nitrite for colourimetric detection using the Griess reagent. Fluid behaviour is significant in microfluidics, as laminar flow is preferable in some applications, while rapid fluid mixing is desired in others. Chapter 5 presents an simple way to tune the fluid mixing in microfluidic chips made by FDM 3D printing by varying the printing orientations. Devices were printed with filament orientations at 0¬¨‚àû, 30¬¨‚àû, 60¬¨‚àû, and 90¬¨‚àû to the direction of the flow. The FDM printed devices with 60¬¨‚àû orientation showed the highest mixing efficiency, while 0¬¨‚àû and 90¬¨‚àû orientations printed chips had the least mixing, thus more laminar fluidic behaviour. Interestingly a rotational fluid flow was also obtained with the 30¬¨‚àû chip. Two chips with laminar flow (0¬¨‚àû filament direction) or mixing flow (+37/‚Äöv†v¿37¬¨‚àû filament direction) were used to perform isotachophoresis and colorimetric detection of iron in river water respectively, demonstrating the simplicity with which the same device can be tuned for different applications simply by controlling the way the device is printed. Based on the results of previous chapters, in Chapter 6 an integrated microfluidic device was fabricated with materials of different functionality. Two membranes with different pore sizes (for extraction, purification, and concentration), and electrodes (for electrokinetic transport) were integrated within a transparent microfluidic body using a 5-head multi material FDM printer in a single fabrication process. The utility of the device was shown by directly measuring the ampicillin level in urine within 3 minutes, and a linear range of 0-100 ppm, showing the potential for low-cost POC diagnostics. In Chapter 7, the findings of this research project are summarized and future directions suggested. This project developed an integrated microfluidic device, and achieved sample-in/answer-out analysis without sample pretreatment, demonstrated by analyzing both biological and environmental samples.