Development of fully functional microfluidic based platforms for rapid on-site water quality analysis
Czugala, Monika (2013) Development of fully functional microfluidic based platforms for rapid on-site water quality analysis. PhD thesis, Dublin City University.
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Environmental monitoring has grown substantially in recent years in response to increasing concerns over the contamination of natural, industrial, and urban areas with potentially harmful chemical agents. Traditional monitoring of water contamination is based upon manual in-situ ‘grab’ sampling followed by laboratory testing. Advantages of this strategy include high precision and accuracy of the measurements, however because of the expense involved in maintaining these facilities there are inherent restrictions in terms of spatial and temporal sampling. In contrast, in-situ measurements generated with portable instruments present a much more scalable model, enabling denser monitoring. The challenge is to develop inexpensive and reliable devices that can be used in-situ, with the capability to make the resulting data available remotely via web-databases, so that water quality can be monitored independently of location. Miniaturisation of analytical devices through the advent of microfluidics has brought wide opportunities for water analysis applications. The vision is to miniaturise processes typically performed in a central clinical lab into small, simple to use devices – so called lab-on-a-chip (LOC) systems. Microfludic systems are especially promising for point-of-care applications due to the low cost, low reagent consumption and portability, and the focus of this thesis is to provide novel microfluidic platforms towards an integrated system for water quality analysis.
A main outcome of my work was the development and validation of innovative integrated systems that were designed and developed for quantitative analysis of turbidity and qualitative analysis of pH and nitrites in water samples. The microfluidic manifolds were designed and fabricated using rapid prototyping techniques such as soft lithography and CO2 laser cutting. For fluid propulsion, various methods were employed: back pressure, capillary forces (typical microfluidic manifolds) and centrifugal force (centrifugal discs). In the latter, fluid propulsion was performed by the forces induced due to the rotation of the disc, thus eliminating the need for external pumps since only a spindle motor is necessary to rotate the disc. Centrifugal discs systems are especially promising for point-of-care applications, and as a final output the fully integrated portable wireless system for in-situ colorimetric analysis was demonstrated. In all systems a low cost but highly sensitive paired emitter- detector diode (PEDD) method was employed to perform colorimetric measurements. Moreover, due to the wireless communication, acquisition parameters were controlled remotely and the results were downloaded from distant locations and displayed in real time. The autonomous capabilities of the system, combined with the portability and wireless communication, provide the basis for a flexible new approach for on-site water monitoring. In addition, their small size and low weight offered the advantage of portability. The suitability of the low-power analysers for the precise and continuous measurement of samples was established, since the analysers exhibited low limits of detection. Freshwater samples were analysed and the results were compared to those generated with a conventional bench-top instruments showing good agreement.
Additionally, stimuli-responsive materials based on N- isopropylacrylamide (NIPAAm) phosphonium ionogels were characterised and incorporated within microfluidic platforms as sensors and actuators. The phase change NIPAAm ionogel functionalised with spirobenzopyran chromophores was characterised and applied for fluid control within microfluidic manifold. Microvalve actuation was performed by the localised white light irradiation, thus allowing for non-contact manipulation of the liquids inside of the microchannels. This is the first time that photoresponsive ionogel microvalves were incorporated within portable, wireless integrated microfluidic analytical platform. Moreover, phosphonium based ionogels incorporating pH sensing dye were used for pH sensing of water samples.
This work presents the core technology for an integrated microfluidic platforms for fundamental research as well as for point-of-use applications.# The key outputs of my work are:
1.Design, fabrication and characterisation of novel microfluidic manifolds.
2.Stimuli-responsive ionogel materials were successfully employed within
microfluidic devices for sensing and actuating applications.
3.Portable, wireless, integrated systems based on microfluidic platforms were developed and their successful application for analysis of pH, turbidity and
nitrites was demonstrated.
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