Components For Lab On Chip Systems

Point of care microsystems also known as lab-on-chips (LOC) are envisaged to revolutionize healthcare in near future. The microfluidics community, for the last 25 to 30 years, has been prolific in developing a myriad of reliable microfluidic devices, each performing a specific task required for the working of a LOC system. Unfortunately, these high performing devices, have their unique fabrication flow process which makes it impossible to fabricate them on a single chip essential for the construction of a LOC system.This thesis is an attempt at bringing components of different functionalities under the hood of a single process flow using glass and silicon as substrates and aluminum as a metal layer. It reports the design and development of a miniaturized Polymerase Chain Reaction (PCR) chip, a capillary microvalve actuated by thermo-pneumatic pressure and finally a capillary microvalve actuated by employing electrohydrodynamic forces.For on chip DNA amplification, a micro-Polymerase Chain Reaction chip is designed and developed with an integrated aluminum microheater with its shape optimized for high temperature uniformity of around 1 K throughout the reactor. A coupled 3D finite element electro-thermal model is employed for this. A proportional integral control is embedded in the finite element model to trace the PCR set temperature. Based on Rayleigh number analysis, overwhelming dominance of conduction over convection for heat dissipation to ambient is found and the problem is reduced to conduction and radiation only. The performance of the microheater was validated by DNA melting point experiments presenting very high temperature uniformity followed by a PCR experiment of 50 cycles of amplification and the results were compared with that of a commercial instrument with and error of 1 unit in the threshold value, CT.Fluidic control using capillary stop valve is a very rewarding approach in microfluidics due to its simplicity in fabrication. A novel method for triggering a capillary stop valve is demonstrated using thermal expansion of trapped air bubble as the actuation element. As in the earlier project, a microheater is integrated as a heating element on the backside of a chamber with a bubble which is trapped while priming the device. The dynamics of the system is studied using the well-known analogous electrical equivalent of a fluidic circuit. The thermal characteristics of the bubble and chip is estimated using finite element (FEM) model which provides temperature as an input to the equivalent circuit model. Experiments are conducted to prove the concept and the image analysis is done to compare with the results of circuit model.As a final contribution, a capillary valve is actuated using electrohydrodynamic forces. This is an open microfluidics device which actuates two capillary valves facing each other simultaneously. Each valve meniscus acts an electrode. The characteristics of the valve is studied using volume of fluid method (VOF), a well-known computational fluid dynamic (CFD) technique where a custom-built pseudo-code known as User Defined Function (UDF) was written in Ansys Fluent software to incorporate electrohydrodynamic effects in the CFD simulations. Experiments were conducted to prove the concept and a failure mechanism proposed to explain the non-coherence of experimental and numerical results.This thesis seeks to bridge the existing knowledge and aspiration of the microfluidics community of a standalone lab-on-chip system through a system level approach to develop lab-on-chip in a seamless process flow.

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