Thread as a substrate for microfluidic diagnostics

Strong need exists in the developing world for affordable diagnostics for health care and environmental monitoring. Diagnostic devices must meet a number of criteria to be suitable for these roles, including being cheap, easily used and transported, but also rapid and accurate, without the need for external equipment. The literature is crowded with studies which employed paper as a substrate for meeting this end, but a recently blossoming field of study has turned to the common thread as an alternative ‐ and this thesis explores diagnostics based on thread exclusively. Advantageous material properties of thread include excellent mechanical strength (compared to paper), flexibility, the ability to form channels without the need for barriers or pre‐treatment, global ubiquitousness, and most importantly – low‐cost. Initial work presented here looked at simple ways to make thread into functional diagnostic devices, such as applying chemical treatments to induce chemical reactions with samples. The first study explored a new take on an old detection technique ‐ using length as opposed to colour intensity to perform a colorimetric analysis. The following study used a simple antibody treatment of thread to create a facile but effective blood typing device which reduced sample volume requirements and was easily interpreted without the need for any external equipment. Users identified a separation of phase in the blood sample added to determine the blood type of the patient. The following chapter focussed on the use of the advanced imaging technique of confocal microscopy to further elucidate the underlying principals which made the thread‐based blood typing technique successful, with the objective of making future optimisation of the test possible. The subsequent part investigated a more complicated mechanism of functionalization to enable thread to be used as a substrate for the detection of organic compounds in aqueous samples. Threads where treated with gold nanoparticles to enable them to perform surface enhanced Raman spectroscopy; a highly accurate and selective analytical technique. The final part of this thesis explored methods of making highly functional and dynamic microfluidic devices using thread. Switches which enabled on‐demand control of fluid flow in thread based devices where fabricated. These functional elements included simple on/off control of liquid flow, selective control of liquid flow to allow the user to choose between one of many outlets/inlets, and finally, a mixing switch which enabled the user to direct two separate inlet flows into a single outlet simultaneously, effectively mixing them together. These devices open the door to much more functional low‐cost microfluidic devices which are capable of chemically transforming analytes prior to detection, all on the same device, or allowing the user to select between multiple tests using the same sample. By exploring these different techniques for enhancing the functionality of thread based microfluidics, this work has given designers of microfluidic diagnostics a variety of new tools ‐ of differing complexity ‐ for creating effective diagnostic devices which could potentially save lives and improve the global health condition.