A Microfabricated Device for the Characterization of Biological Entities
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A MICROFABRICATED DEVICE FOR THE CHARACTERIZATION OF BIOLOGICAL ENTITIES♣ H. Chang1, A. Ikram1, M. Young1, F. Kosari2, G. Vasmatzis2, A. Bhunia3, and R. Bashir1,4, ∆ School of Electrical and Computer Engineering, 3Department of Food Sciences, 4Department of Biomedical Engineering, Purdue University, W. Lafayette, IN. 2Mayo Clinic, Rochester MN.
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Abstract A micro-fabricated pore is constructed and tested so that it can be used to characterize biological entities. The pore is prepared by bulk micro-machining of a silicon wafer. An oxide coated silicon diaphragm with the pore is placed between two chambers containing ionic buffer solutions to mimic a bilayer system. If a voltage is applied across the pore, electrophoretic passage of charged entities can be electrically detected through changes in the ionic current flow. When the entities traverse the pore, the ionic current is blocked and a decrease in the current can be observed. As an initial test case, negatively charged polystyrene beads which were PLQ diameter, were electrophoretically driven across the pore. Then the bacterium Listeria innocua, suspended in Tris-glycine buffer, was also electrophoretically driven through the pore and its effective mobility was extracted. The device can also be used to study the interactions between organisms and the micro-fabricated surfaces. Work is continuing to scale the pore to the sub100A range to be used for characterization and possible sequencing of single molecules such as DNA.
Introduction Biological entities such as cells, proteins, and DNA carry charges and can be made to move under an applied electric field. The drift of these entities has been used as a way to obtain important information such as their charge, length, electrophoretic mobility, etc. [1, 2]. Such analyses are typically carried out on samples with many entities and the information obtained, such as the mobility, represents an average value for the ensemble. The possible characterization of single entities and molecules is very attractive for conducting basic scientific studies and for practical applications such as ultra-sensitive detection and diagnosis. A device with a single pore, mimicking an ion channel, for the characterization of single entities can be very useful for applications. In fact, such biological nano-pores for the characterization of single DNA molecules have been demonstrated [3]. Kasianowicz, et al. reported the use of a single αhemolysin channel in a lipid bilayer to electronically detect the passage of double stranded DNA through the channel. Subsequently, Meller, et al. [4] reported the use of the same nano-pore to distinguish between polynucleotides due to differences in their sequence. In both of these studies, the electronic detection was achieved by monitoring the decrease in the ionic current flow through the pore when the entities of interest would traverse through the pore. Hence, the molecule of interest would block the background ionic current flow and this decrease in current would be detected.
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