Carbon nanotube membranes for electrokinetic separation of proteins

The purpose of this dissertation is to demonstrate the feasibility of using carbon nanotube membranes (CNTMs) to electrophoretically separate proteins based on their molecular weights (MW). The microfluidic device incorporating the CNTM was fabricated by traditional microfabrication techniques and thermal chemical vapor deposition (CVD). Preliminary electrophoretic testing indicated a lack of migration of fluorescent dye through a 1-mm long pad of CNTM due to the electrically conductive nature of CNTs. Efforts to minimize the conductive nature of the CNTs on the electric field prompted the use of 40-um long strips of CNTMs, which produced a voltage gradient similar to that of an empty channel and allowed complete migration of the dye. The fluorescently labeled non-denatured proteins of various MWs (6.5--- 97 kDa) were electrokinetically flowed through the microchannels in separate identical electriophoresis runs as well as in mixture form and observed through a fluorescent microscope. Proteins larger than or equal to 20 kDa accumulated ahead of the CNTMs, whereas, proteins smaller than or equal to 17 kDa freely migrated the CNTMs and no accumulation was observed, indicating that the protein build-up was due to the larger size of the higher MW proteins. More interestingly in addition to accumulation ahead of the CNTMs, mixtures of proteins larger than 20 kDa separated from each other and formed spatially-distinguished bands that were arranged in the increasing order of their MWs, such that the smallest protein accumulated against the CNTM, the next higher MW protein accumulated against the smallest protein and so on. Separation of protein components from 2-protein and 3-proteins mixtures (composed of Protein A [42 kDa], Neutravidin [66 kDa] and Phosphorylalse B [97 kDa], each labeled with a different fluorophore) was also verified by mapping pixel intensity of individual proteins to their locations inside the microchannel. The effect of CNTM geometry was evaluated and a 60 lm long CNTM strip in a 500 tm wide channel produced the best separation in terms of spatial discrimination between proteins.