ENGRI1110_Lect31_Nov11_posted - Read Preface, 57-79...

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Unformatted text preview: Read Preface, 57-79 Nanotechs Promise Debating Nanotechnologies Flexibility in pore diameter and pore length Interaction with single nucleotides ~20 nucleotides in aHL simultaneously High stability (temperature, pH, salt, ..) Slower translocation 1-5 ms /nucleotide in aHL Adjustable surface properties of the pore Allows integration into devices and arrays Lifetime High Mechanical Robustness, Voltage Range Electronic Noise from Large Membrane Capacitance hemolysin is toxic and hard to work with After a decade of using protein pores, efforts are underway in many groups to develop synthetic pores (such as in Silicon Nitride): Solid State Nanopores Solid State Nanopores Nanopores and DNA Nanopores and DNA Pull DNA through a pore by applying a voltage Blockade current Chen et al., Nano Lett. (2004) Kasianowicz et al., Proc. Natl. Acad. Sci. (1996) DNA is a strong acid in aqueous solution The negative charge distribution along DNA molecule is non-uniform and almost point-like The maxima of this distribution are located on phosphate groups of the molecules helical backbone The charge localized at these atoms is close to that of a single electron Use Charge to Trap DNA A nanopore of radius r slightly exceeding r helix penetrates through a membrane that separates two reservoirs The membrane is a sandwich of three metal electrodes separated by insulators. The voltage difference between central and side electrode is kept at V . An independent voltage difference applied between two reservoirs drives the ssDNA inside the nanopore. The phosphate charges are in close proximity to the walls of the nanopore. DNA Transistor http://www-03.ibm.com/press/us/en/pressrelease/28558.wss Positive voltage applied to central electrode creates attractive electrostatic potential: negative charge on DNA backbone stuck in a trap with energy = 170 meV With zero applied voltage, DNA moves in a direction through the pore determined by the voltage across aqueous reservoirs Negative voltage on electrode makes negative charges on backbone want move away from electrode: also a trap DNA moves by a distance that is equal to length of charge separation: 0.34 nm Oscillating the voltage will move molecule one base pair at a time Applications Near-term: Count number of bases on molecules Replace gel electrophoresis with digital electrophoresis Requires less amplification of DNA Long-term: Sequence the bases A,T,G,C may give different currents across electrodes A,T,G,C may have different optical properties Electronic transport Electronic transport Regardless of measuring apparatus, how distinguishable are the bases in principle?...
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ENGRI1110_Lect31_Nov11_posted - Read Preface, 57-79...

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