Microfluidic Devices for Single Molecule Detection and On-Chip Pressure Measurement

Lab-on-a-chip technologies have been employed in many fields of research. Molecular analysis, microelectronics, chemical and biological assays, cellular studies and environmental monitoring are a few examples in a large and varied list of microfluidic applications. This thesis covers areas from soft matter polymer physics to cancer diagnosis and super resolution microscopy. The first topic is immunoassay or the detection of cancer biomarkers on chip. The importance of early cancer detection lies in the massive increase in treat- ment effectiveness the sooner it is administered. In this thesis, the detection of Prostate Specific Antigen (PSA) is investigated using on-chip immunoassay. The components of the immunoassay have been characterised from enzyme reporters to microfluidic droplet generation mechanisms. Single molecules of enzyme can be detected paving the way for on-chip cancer diagnosis. Many microfluidic devices are manufactured from polydimethylsiloxane(PDMS), a soft polymer. The material has many advantages in microfluidics from optical transparency, low cost, ease of handling, gas permeability and biocompatibility. Due to its elastic properties, PDMS is prone to deformation when placed under high pressures. A novel method of pressure measurement is presented. Along with pressure measurements, the interaction between PDMS and molecules that diffuse into it are studied. The infiltration of molecules changes local mechanical properties which effects the internal pressure of a channel. Raman spectroscopy allows visualisation of the dynamics of material ingress. Expansion microscopy is a method of encasing a biological sample in a gel matrix, removing the sample and leaving behind a fluorescent ghost image. This gel swells isotropically in water so the fluorescent markers move further apart and can be resolved through super resolution microscopy. This requires delicate handling and the development of devices shown here may assist in containing the entire protocol