Numerical and experimental investigations of ESI and DESI performance of microfluidic devices for proteomic analysis

Proteomics deals with extensive study of proteins including their structure and function. The use of proteomics has been realized and implemented in the discovery of biomarkers that indicate a particular disease and identification of potential new drug targets for the treatment of a disease. Protein mixtures can be analyzed without prior separation using 2D-liquid chromatography in which the protein mixture is digested and the resulting peptides are injected onto a reversed phase (RP) high performance liquid chromatography (HPLC) column. The RP-HPLC column separates peptides based on hydrophobicity and the peptides eluted from these columns can be identified by combining mass spectrometry (MS) with electrospray ionization (ESI) or desorption electrospray ionization (DESI).; This work deals with numerical and experimental investigations of ESI-MS and DESI-MS performance of microfluidic devices for proteomic analysis. A numerical model is presented that is used for simulating the electrospray process including the Taylor cone-jet, jet breakup, and droplet dynamics and fission regimes. The cone-jet model considers leaky-dielectric formulations for solving the cone-jet dynamics and volume of fluid method for tracking the free-surface. The jet breakup was simulated by introducing a sinusoidal velocity perturbation at the capillary inlet. The droplet dynamics were simulated considering motion of liquid droplets in a steady gas medium and the fission process is simulated based on the principle of minimum free energy. The model is validated using experimental results reported in literature for conventional single-jet and multi-jet emitters. The model was then applied to simulate the electrospray performance of a carbon fiber-based single-jet and carbon nanofiber-based multi-jet microfluidic devices. The influences of design factors, geometric and operating conditions on the performance of the devices are thoroughly investigated.; This work also presents use of a nanoporous alumina surface for DESI. The DESI-MS performance of the porous alumina surface is compared with that of PMMA, PTFE and glass that are popular surfaces in DESI-MS experiments. A microfluidic nebulizer chip utilizing either Nanoport(TM) connections or a new interconnection system is also presented. The design, microfabrication and test of the nebulizer chip are thoroughly discussed. Also, design and fabrication of the Nanoport(TM) and the new interconnection system used for making external connections to the nebulizer chip are presented. Leakage tests were performed to demonstrate that the interconnection systems are leak-free and to measure the burst pressure of the interconnection systems. The performance of the new interconnection system is compared with that of the Nanoport(TM) interconnection system. Finally, DESI-MS performance of the microfluidic nebulizer chip is compared with that of a conventional DESI nebulizer.