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Graphene nanopore support system for simultaneous high-resolution AFM imaging and conductance measurements.

Connelly LS, Meckes B, Larkin J, Gillman AL, Wanunu M, Lal R - ACS Appl Mater Interfaces (2014)

Bottom Line: Atomic force microscopy (AFM) can image the structures of these pores at high resolution in an aqueous environment, and electrophysiological techniques can measure ion flow through individual nanoscale pores.Combining these techniques is limited by the lack of nanoscale interfaces.The functionality of this integrated system is demonstrated by electrical recording (<10 pS conductance) of suspended lipid bilayers spanning a nanopore and simultaneous AFM imaging of the bilayer.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Engineering Program, ‡Department of Bioengineering, and §Department of Mechanical and Aerospace Engineering, University of California-San Diego , 9500 Gilman Drive, La Jolla, California 92093, United States.

ABSTRACT
Accurately defining the nanoporous structure and sensing the ionic flow across nanoscale pores in thin films and membranes has a wide range of applications, including characterization of biological ion channels and receptors, DNA sequencing, molecule separation by nanoparticle films, sensing by block co-polymers films, and catalysis through metal-organic frameworks. Ionic conductance through nanopores is often regulated by their 3D structures, a relationship that can be accurately determined only by their simultaneous measurements. However, defining their structure-function relationships directly by any existing techniques is still not possible. Atomic force microscopy (AFM) can image the structures of these pores at high resolution in an aqueous environment, and electrophysiological techniques can measure ion flow through individual nanoscale pores. Combining these techniques is limited by the lack of nanoscale interfaces. We have designed a graphene-based single-nanopore support (∼5 nm thick with ∼20 nm pore diameter) and have integrated AFM imaging and ionic conductance recording using our newly designed double-chamber recording system to study an overlaid thin film. The functionality of this integrated system is demonstrated by electrical recording (<10 pS conductance) of suspended lipid bilayers spanning a nanopore and simultaneous AFM imaging of the bilayer.

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(A) Top-view SEM image of the drilled FIB 1μm hole. Inset is a zoomed-out SEM image of the same hole. The20 × 20 μm2 SiO2 window is visiblein the SEM image. Scale bar = 1 μm. (B) TEM image of the drilledFIB 1 μm hole covered with a layer of graphene showing no defects.Thicker regions appear darker. Scale bar = 500 nm. (C) TEM image ofa single drilled 20 nm pore in the graphene/Al2O3 membrane. Scale bar = 20 nm.
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fig3: (A) Top-view SEM image of the drilled FIB 1μm hole. Inset is a zoomed-out SEM image of the same hole. The20 × 20 μm2 SiO2 window is visiblein the SEM image. Scale bar = 1 μm. (B) TEM image of the drilledFIB 1 μm hole covered with a layer of graphene showing no defects.Thicker regions appear darker. Scale bar = 500 nm. (C) TEM image ofa single drilled 20 nm pore in the graphene/Al2O3 membrane. Scale bar = 20 nm.

Mentions: Siliconoxide membranes (SiO2) were purchased from AppNano (MountainView, CA). Silicon oxide membranes are 200 nm thick and 20 ×20 μm2 wide freestanding windows supported by a 300μm thick silicon substrate. The windows were formed by KOH anisotropicetching of a 450 × 450 μm2 opening on the backsideof the silicon support (Figures 2A and 3A). Single-layer CVD graphene deposited on 20 μmthick Cu foil (2 × 2″) was obtained from Graphene Supermarket(Calverton, NY). A Quanta 3D FEG focused ion beam (FIB) was used todrill through the SiO2 suspended membrane. Either an iron(III)chloride hexahydrate (FeCl3·6H2O; ≥98%) solution (Sigma Aldrich) or Copper Etch APS-100 (Transene Co.)was used to dissolve the Cu substrate of the graphene. Atomic layerdeposition (ALD) of 5 nm of Al2O3 was performedusing a GEMSTAR benchtop atomic layer deposition (ALD) process systemor the Beneq TFS200 atomic layer deposition system. A transmissionelectron microscope (TEM) (JEOL 2010FEG, Japan) operating in bright-fieldimaging mode was used for drilling through the graphene/Al2O3 membrane layer. AFM imaging was completed using a multimodeNanoscope IV system and liquid cell (both from Bruker, Santa Barbara,CA) with silicon nitride cantilevers (k = 0.08 N/m,Asylum Research, Santa Barbara, CA). Conductance measurements werecompleted using a custom-designed Lexan polycarbonate double-chambercup (Figure 1C) and Ag/AgCl wire electrodes.Ecoflex Supersoft 5 silicone-cured rubber was used as an insulatingsealant of the nanopore sample in the double-chamber cup. A patch-clampamplifier (Dagan, Minneapolis, MN) was used for amplifying currents.Electrolyte solutions at pH 8.5 containing 1 M KCl buffered with 10mM Tris, similar to Venkatesan et al., was used for AFM imaging inliquid and conductance measurements.45 Thephospholipid 1,2-diphytanoyl-sn-glycero-3-phosphocholine(DiPhyPC) was purchased from Avanti Polar Lipids (Alabaster, AL).


Graphene nanopore support system for simultaneous high-resolution AFM imaging and conductance measurements.

Connelly LS, Meckes B, Larkin J, Gillman AL, Wanunu M, Lal R - ACS Appl Mater Interfaces (2014)

(A) Top-view SEM image of the drilled FIB 1μm hole. Inset is a zoomed-out SEM image of the same hole. The20 × 20 μm2 SiO2 window is visiblein the SEM image. Scale bar = 1 μm. (B) TEM image of the drilledFIB 1 μm hole covered with a layer of graphene showing no defects.Thicker regions appear darker. Scale bar = 500 nm. (C) TEM image ofa single drilled 20 nm pore in the graphene/Al2O3 membrane. Scale bar = 20 nm.
© Copyright Policy
Related In: Results  -  Collection

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fig3: (A) Top-view SEM image of the drilled FIB 1μm hole. Inset is a zoomed-out SEM image of the same hole. The20 × 20 μm2 SiO2 window is visiblein the SEM image. Scale bar = 1 μm. (B) TEM image of the drilledFIB 1 μm hole covered with a layer of graphene showing no defects.Thicker regions appear darker. Scale bar = 500 nm. (C) TEM image ofa single drilled 20 nm pore in the graphene/Al2O3 membrane. Scale bar = 20 nm.
Mentions: Siliconoxide membranes (SiO2) were purchased from AppNano (MountainView, CA). Silicon oxide membranes are 200 nm thick and 20 ×20 μm2 wide freestanding windows supported by a 300μm thick silicon substrate. The windows were formed by KOH anisotropicetching of a 450 × 450 μm2 opening on the backsideof the silicon support (Figures 2A and 3A). Single-layer CVD graphene deposited on 20 μmthick Cu foil (2 × 2″) was obtained from Graphene Supermarket(Calverton, NY). A Quanta 3D FEG focused ion beam (FIB) was used todrill through the SiO2 suspended membrane. Either an iron(III)chloride hexahydrate (FeCl3·6H2O; ≥98%) solution (Sigma Aldrich) or Copper Etch APS-100 (Transene Co.)was used to dissolve the Cu substrate of the graphene. Atomic layerdeposition (ALD) of 5 nm of Al2O3 was performedusing a GEMSTAR benchtop atomic layer deposition (ALD) process systemor the Beneq TFS200 atomic layer deposition system. A transmissionelectron microscope (TEM) (JEOL 2010FEG, Japan) operating in bright-fieldimaging mode was used for drilling through the graphene/Al2O3 membrane layer. AFM imaging was completed using a multimodeNanoscope IV system and liquid cell (both from Bruker, Santa Barbara,CA) with silicon nitride cantilevers (k = 0.08 N/m,Asylum Research, Santa Barbara, CA). Conductance measurements werecompleted using a custom-designed Lexan polycarbonate double-chambercup (Figure 1C) and Ag/AgCl wire electrodes.Ecoflex Supersoft 5 silicone-cured rubber was used as an insulatingsealant of the nanopore sample in the double-chamber cup. A patch-clampamplifier (Dagan, Minneapolis, MN) was used for amplifying currents.Electrolyte solutions at pH 8.5 containing 1 M KCl buffered with 10mM Tris, similar to Venkatesan et al., was used for AFM imaging inliquid and conductance measurements.45 Thephospholipid 1,2-diphytanoyl-sn-glycero-3-phosphocholine(DiPhyPC) was purchased from Avanti Polar Lipids (Alabaster, AL).

Bottom Line: Atomic force microscopy (AFM) can image the structures of these pores at high resolution in an aqueous environment, and electrophysiological techniques can measure ion flow through individual nanoscale pores.Combining these techniques is limited by the lack of nanoscale interfaces.The functionality of this integrated system is demonstrated by electrical recording (<10 pS conductance) of suspended lipid bilayers spanning a nanopore and simultaneous AFM imaging of the bilayer.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Engineering Program, ‡Department of Bioengineering, and §Department of Mechanical and Aerospace Engineering, University of California-San Diego , 9500 Gilman Drive, La Jolla, California 92093, United States.

ABSTRACT
Accurately defining the nanoporous structure and sensing the ionic flow across nanoscale pores in thin films and membranes has a wide range of applications, including characterization of biological ion channels and receptors, DNA sequencing, molecule separation by nanoparticle films, sensing by block co-polymers films, and catalysis through metal-organic frameworks. Ionic conductance through nanopores is often regulated by their 3D structures, a relationship that can be accurately determined only by their simultaneous measurements. However, defining their structure-function relationships directly by any existing techniques is still not possible. Atomic force microscopy (AFM) can image the structures of these pores at high resolution in an aqueous environment, and electrophysiological techniques can measure ion flow through individual nanoscale pores. Combining these techniques is limited by the lack of nanoscale interfaces. We have designed a graphene-based single-nanopore support (∼5 nm thick with ∼20 nm pore diameter) and have integrated AFM imaging and ionic conductance recording using our newly designed double-chamber recording system to study an overlaid thin film. The functionality of this integrated system is demonstrated by electrical recording (<10 pS conductance) of suspended lipid bilayers spanning a nanopore and simultaneous AFM imaging of the bilayer.

Show MeSH
Related in: MedlinePlus