Heins05

Heins05 - NANO LETTERS Detecting Single Porphyrin Molecules...

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Detecting Single Porphyrin Molecules in a Conically Shaped Synthetic Nanopore Elizabeth A. Heins, Zuzanna S. Siwy, Lane A. Baker, and Charles R. Martin* Department of Chemistry and Center for Research at the Bio/Nano Interface, Uni V ersity of Florida, Gaines V ille, Florida 32611-7200 Received May 18, 2005; Revised Manuscript Received July 14, 2005 ABSTRACT We report here the first example of abiotic resistive-pulse sensing of a molecular (as opposed to a particle or macromolecular) analyte. This was accomplished by using a conically shaped nanopore prepared by the track-etch method as the sensing element. It is possible to sense the molecular analyte because the small diameter opening of the conical nanopore ( 4.5 nm) is comparable to the diameter of the analyte molecule ( 2 nm). Introduction. There is increasing interest in using nanopores as the sensing elements in biosensors. 1 - 15 The R -hemolysin protein nanopore is typically used, and the sensor consists of a single protein nanopore embedded within a lipid bilayer membrane. 1 - 9 An ionic current is passed through the nanopore, and analyte species are detected as transient blocks in this current associated with translocation of the analyte through the pore. This technique has been called stochastic sensing in the literature, but is included in the more general class of sensing technologies called resistive-pulse sensing. 1 Both wild-type and engineered R -hemolysin nanopores have been used to sense a wide range of analytes including metal ions, 4 DNA, 5,6 proteins, 7 and polymers. 8 Small molecule analytes can also be sensed this way, provided that the molecule can be sequestered in a larger species such as a cyclodextrin. 9 Although this is a very promising sensing paradigm, it would be advantageous to eliminate the fragile lipid bilayer membrane and perhaps to replace the biological nanopore with an abiotic equivalent. 10 - 22 A variety of approaches have been used to prepare abiotic nanopores for sensing applica- tions, including focused ion beam etching of silicon nitride and oxide, 10,11,14,15 soft lithographic techniques, 13 embedded carbon nanotubes, 16 and track-etched conical nanopores produced in polymeric membranes. 17 - 22 To date, the only analytes to be sensed via the resistive-pulse approach with such abiotic nanopores are nanoparticles 16,21 and large DNA molecules. 10,12,13,15 Biofunctionalized gold nanotubes have been used to detect protein analytes but not via the resistive- pulse method. 22 We report here the first example of abiotic resistive-pulse sensing of a molecular (as opposed to a particle or macromolecular) analyte. This was accomplished by using a conically shaped nanopore 17 - 22 prepared by the track-etch method 23 as the sensing element. It is possible to sense this molecular analyte (Scheme 1) because the small diameter opening of the conical nanopore is comparable to the diameter of this molecule. Experimental Section.
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Heins05 - NANO LETTERS Detecting Single Porphyrin Molecules...

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