Development of Multi-Nozzle Emitters for Nano-ESI Mass Spectrometry and Fabrication of 1D Polymer Structures Using Microstructured Fibers as Templates
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Nano-electrospray ionization mass spectrometry (nano-ESI-MS) has become an important analytical tool due to its high sensitivity through improved desolvation from smaller droplet production as well as high sample utilization due to reduced solvent and sample consumption. The reliability and sensitivity of nano-ESI-MS is largely dependent on the properties of the emitter. However, the standard single-aperture, tapered nano-ESI emitters have some serious limitations including high clogging tendency, poor robustness, and narrow flow rate range. To address these problems, emitters generating multiple electrosprays (MESs) have been explored, offering significantly improved sensitivity by splitting the flow into smaller streams and higher clogging resistance from multiple paths. The objective of this thesis is to develop MES emitters based on microstructured fibers (MSFs) to conquer the limitations associated with the standard emitters meanwhile to maintain higher flow rates more compatible with front-end separation techniques. MSF, a fiber having many hollow channels running along its length was chosen to develop nano-ESI emitters because of its dimensional compatibility, structural consistency, design diversity, and feasibility for surface modification, providing a convenient and customizable template material. First, a multi-nozzle emitter was developed using a commercial MSF with an array of polymer nozzles fabricated by optimized procedures involving in-situ polymerization of microtubes in the channels and wet chemical etching of the silica at the tip to form the nozzles. However, no MES behaviour was observed due to the densely packed channel pattern. Custom MSFs were subsequently designed and fabricated with nine or six channels arranged in a radial pattern to promote MES. While the MSFs themselves did not support MES, the formation of nozzles made by either polymer or silica at the tip face enables independent electrospray from each nozzle, showing MES behaviour with significant signal enhancement relative to a standard emitter at the same total flow rate. Furthermore, a variety of MSFs were used as templates to fabricate one-dimensional polymer microstructures including tubes, wires and porous monoliths. Because of the properties of the MSFs, the structures formed from these template channels share their low polydispersity, ultrahigh aspect ratio and axial alignment, showing great applicability in diverse fields.