Title: Polymer-Based MEMS Calorimetric Devices for Characterization of Biomolecular Interactions
Description: Biomolecular interactions are central to all biological functions as the execution of biological function usually depends on the concerted action of biomolecules existing in protein complexes, metabolic or signaling pathways or networks. Therefore, understanding biomolecular interactions, and the temperature dependence of biomolecular interactions is of critical importance for the study of fundamental science, therapeutic drug development, and biomolecule manipulation. Biocalorimetry, a process of measuring the heat involved in biomolecular interactions, has distinct advantages over other biomoelcualr interactions characterization methods as it is solution based, label free, universally applicable, and allows for determination of thermodynamic propoerties. However, the utility of available commercial instruments is limited by complex design, rather large sample consumption, and slow responses. Micro-electro-mechanical systems (MEMS) technology, as an alternative approach, potentially offers solutions to such limitations as it can potentially be fabricated at low cost, operated at high throughput with minimum sample consumption, and available for integration with various functional units.

However, existing MEMS calorimeters either do not yet allow proper control of reaction conditions for thermodynamic characterization of biomolecular reaction systems or is not yet suitable for practical applications because of a lack of sensitivity, reliability, and high operating cost. This thesis will build upon our existing knowledge of the MEMS technology in biocalorimetry and develop new generation of polymer MEMS calorimetric devices that are economical, sensitive, and robust for studying biomolecular characterization in practical settings. The development of such devices requires innovations in the fabrication process as the conventional photolithography process is largely incompatible with polymer substrates. To address that, this thesis first presents a novel method of fabricating polymer-based MEMS thermoelectric sensors using a thermally assisted lift-off approach, by which, thick metal or semiconductor films experience controlled breakup due to thermal reflow of the underlying lithographically defined patterns.

The thick film MEMS thermoelectric sensors exhibit electric and thermoelectric performances comparable to those made from bulk materials. This allows the sensors to be useful in low-noise, high-efficiency thermoelectric measurements. The polymer-based MEMS sensors fabrication approach is then implemented in making MEMS calorimetric devices for solution-based, quantitative thermodynamic characterization of biomolecular interactions. This thesis presents both polymer-based MEMS differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC) devices that are more robust, and cost lower. The polymer-based MEMS calorimeters eliminate the need for complex, fragile silicon freestanding structures and offer real-time, in-situ temperature control to biomolecules with well-defined miniature volume. Combining with the improved sensitivity, the polymer-based devices also reduce consumption of material and leads to substantially reduced thermal mass of the measurement system for a rapid response time and improved throughput.

The interpretation of the DSC, ITC measurement results yielded complete thermodynamic information of several biomolecular interactions of critical scientific and therapeutic interest that include the characterization of the unfolding of protein (lysozyme) for the determination of its thermodynamic properties, and the binding parameters of interactions of 18-Crown-6 and barium chloride in practically applicable reagent concentrations. In addition, PDMS-based microfluidic structures that are used in molecular biological analysis platforms, including MEMS calorimeters are known to be problematic due to its surface adsorption effects and high permeability. To address this, this thesis eliminates the use of PDMS microfluidic structures in MEMS calorimeters entirely by presenting the first demonstration of a miniaturized 3D-printed Lab-on-a-chip (LOC) platform that integrates the polymer-based MEMS calorimeter for quantitative ITC characterization of biomolecular interactions. Exploiting topographical flexibility offered by 3D printing, the platform design features fully isolated cantilever-like calorimetric measurement structures in a differential setup.

This design layout improves thermal isolation and reduces overall platform thermal mass, thereby enhancing the measurement sensitivity and reducing the platform response time. The utility of the platform is demonstrated with ITC measurements of the binding of 18-Crown-6 with barium chloride and the binding of ribonuclease A with cytidine 2’-monophosphate in a reusable manner, and with practically relevant reagent concentrations. Finally, some perspectives of how far away the devices are from commercializing are summarized, and future works in suggesting the strategies to achieve this goal are proposed.