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. 2009 Jul 20;21(27):2771.
doi: 10.1002/adma.200803786.

Highly Sensitive, Mechanically Stable Nanopore Sensors for DNA Analysis

Bala Murali Venkatesan  1 , Brian Dorvel, Sukru Yemenicioglu, Nicholas Watkins, Ivan Petrov, Rashid Bashir
Affiliations

Highly Sensitive, Mechanically Stable Nanopore Sensors for DNA Analysis

Bala Murali Venkatesan et al. Adv Mater. .
No abstract available

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Figures

Figure 1
Figure 1
Process flow for the formation of Al2O3 nanopores. a) Start with double-side polished 300 μm thick Silicon wafer. b) Deposit 70 nm of Al2O3 by ALD. c) Deposit 500 nm low-stress SiN using PECVD process. d) Pattern 30 μm × 30 μm windows on the wafer front side via optical lithography and RIE. e) Pattern 30 μm × 30 μm windows on the wafer backside and etch using DRIE (SF6 + O2), and stop on the Al2O3 layer creating a membrane. f) Use a tightly focused electron beam to form nanometer-sized pores.
Figure 2
Figure 2
a) SEM image of backside trench formed using DRIE. b) SEM cross-section at 5° tilt of Al2O3 membrane with supporting SiN layer. Membrane is under low tensile stress and appears flat. c) SEM cross-section at 5° tilt of SiO2 membrane post-oxidation showing ∼5 μm vertical deflection over 50 μm span due to high compressive stress. Membrane is significantly deformed resulting in frequent failure.
Figure 3
Figure 3
a–d) TEM phase-contrast images illustrating temporal contraction of an Al2O3 nanopore from an initial pore size of ∼4 nm to a final pore size of ∼1 nm. e) TEM phase-contrast image of 4 nm SiN pore. f) Corresponding FFT showing amorphous structure of SiN pore. g) TEM phase-contrast image of a 4 nm Al2O3 pore. Hexagonal Al2O3 nanocrystallites are shown by i, ii, iii, iv. iv is partially aligned with the zone axis with 2.28 Å atomic spacing corresponding to γ-Al2O3 in its 〈222〉 crystal orientation. h) Corresponding FFT showing polycrystalline structure of the pore.
Figure 4
Figure 4
a) XPS results on Al2O3 films. Inset: Auger differential spectra of membrane region postrelease illustrating presence of only Al and O. b) Depth profiling using AES to extract membrane thickness of 60 ± 2 nm. Inset: tilted SEM image of membrane with marked region indicating Auger electron collection region.
Figure 5
Figure 5
a) I–V characteristics of an 11.1 nm diameter pore measured in 10 mm KCl, 100 mm KCl, and 1 m KCl. Linear I–V characteristics suggest symmetric pore geometry. b) Pore conductance of 11 nanopores ranging in diameter from 4 to 16 nm. Red and blue lines represent conductance models from literature. Black line is a least-squares fit to the measured data. Predicted geometry of pore from conductance measurements. Left inset: thickness mapping of an 11.1 nm pore constructed using EFTEM. c) Power spectra of three different Al2O3 nanopores in 1 m KCl at 120 mV. Spectral components at high frequencies (f> 1 kHz) are significantly attenuated relative to Si3N4 and SiO2 systems.[14,15]
Figure 6
Figure 6
a) Typical current blockades seen in a 5.3 nm Al2O3 pore after the addition of 5 kbp dsDNA at a concentration of 6 nm at 500 mV. Data is low-pass filtered at 100 kHz. Left inset: negative control: pore current prior to the introduction of DNA is steady, no blockades are seen. Right inset: typical current blockade with annotations. b) Blockage ratio (Br) versus event dwell time (tD) for n = 1178 events. Primarily, a single blockade level with (Br) = 0.17 is seen. Inset: corresponding event-dwell-time histogram with time constant t = 1.97 ± 0.2 ms. Broad dwell-time distribution with large time constant suggests that events are DNA translocations rather than rapid collisions.
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