Towards the design of a paper-based microfluidic sensor for water quality monitoring and comparative life cycle assessment

Point-of-care devices have the potential to revolutionize public health care in both developing and developed countries. In today’s society, rapid, relatively inexpensive, disposable tests are becoming an important necessity, particularly for tracing the sources of infectious diseases. On the other hand, these devices can be a key to the development of developing countries where access to safe and sufficient water is not yet assured. In recent years, interest in point-of-care screening devices has increased and is expected to continue to grow, in particular due to changes in the need for health care. The project that led to this master’s thesis aims to create a prototype point-of-care screening device suitable for use in developing countries. This affordable, portable and sensitive biosensor will consist of a disposable paper-based platform that will allow microflow of a water sample and electrical detection of harmful E. coli bacteria. Although the detection of E. coli in a developing country is the intended application, these devices may have different uses. The emergence in 2019 of the new coronavirus disease (COVID-19) has highlighted one of them. The biosensor to be studied could meet the need for detection of various viruses in the coming years through appropriate modifications. In this work the use of a nitrocellulose membrane as biosensor substrate for the detection of E. coli bacteria from a water matrix is discussed. It is conducted by the study of microfluidics in the nitrocellulose through a discussion of design parameters impact on the biosensor response, and by the introduction of membrane biofunctionalization by phage receptor binding proteins (RBPs) and cell binding domains (CBDs). The test sensitivity is mainly affected by the capillary flow rate of the water sample at the specific test line location. Even if smallest pores sizes lead to a smaller flow rate, high ones allow an easiest displacement of target particles through the device so that this type of membrane should be preferred. The capillary flow rate could be controlled by adapted sudden change in the strip width. The volume of analyzed sample is also a parameter playing a role on the sensitivity of the device. It is related to the void volume downstream the capture line and the addition of an absorbent pad (i.e. a chromatography paper) at the top of the strip can be used to increase the volume of sample flowing through the test line. Nitrocellulose is of high interest as biosensor substrate thanks to its very good properties of immobilizing biomolecules. In this work the first biofunctionalization experiences are done with receptors specific to the Bacillus cereus group. This approach "proof-of-concept" highlights that phages RBPs and CBDs are good candidates to be used as bioreceptors. The choice of the nitrocellulose support for microfluidics needs compared to the PDMS one is confirmed thanks to a comparative life cycle assessment (LCA) comparing their embodied energy and their carbon footprint.