DNA molecular wires have been studied extensively because of the ease with which molecules of con... more DNA molecular wires have been studied extensively because of the ease with which molecules of controlled length and composition can be synthesized. The same has not been true for proteins. Here, we have synthesized and studied a series of consensus tetratricopeptide repeat (CTPR) proteins, spanning 4 to 20 nm in length, in increments of 4 nm. For lengths in excess of 6 nm, their conductance exceeds that of the canonical molecular wire, oligo(phenylene-ethylenene), because of the more gradual decay of conductance with length in the protein. We show that, while the conductance decay fits an exponential (characteristic of quantum tunneling) and not a linear increase of resistance with length (characteristic of hopping transport), it is also accounted for by a square-law dependence on length (characteristic of weakly driven hopping). Measurements of the energy dependence of the decay length rule out the quantum tunneling case. A resonance in the carrier injection energy shows that allowed states in the protein align with the Fermi energy of the electrodes. Both the energy of these states and the long-range of hopping suggest that the reorganization induced by hole formation is greatly reduced inside the protein. We outline a model for calculating the molecular-electronic properties of proteins.
Driven by the curiosity for the secret of life, the effort on sequencing of DNAs and other large ... more Driven by the curiosity for the secret of life, the effort on sequencing of DNAs and other large biopolymers has never been respited. Advanced from recent sequencing techniques, nanotube and nanopore based sequencing has been attracting much attention. This thesis focuses on the study of first and crucial compartment of the third generation sequencing technique, the capture and translocation of biopolymers, and discuss the advantages and obstacles of two different nanofluidic pathways, nanotubes and nanopores for single molecule capturing and translocation. Carbon nanotubes with its constrained structure, the frictionless inner wall and strong electroosmotic flow, are promising materials for linearly threading DNA and other biopolymers for sequencing. Solid state nanopore on the other hand, is a robust chemical, thermal and mechanical stable nanofluidic device, which has a high capturing rate and, to some extent, good controllable threading ability for DNA and other biomolecules. These two different but similar nanofluidic pathways both provide a good preparation of analyte molecules for the sequencing purpose. In addition, more and more research interests have move onto peptide chains and protein sensing. For proteome is better and more direct indicators for human health, peptide chains and protein sensing have a much wider range of applications on bio-medicine, disease early diagnoses, and etc. A universal peptide chain nanopore sensing technique with universal chemical modification of peptides is discussed in this thesis as well, which unifies the nanopore capturing process for vast varieties of peptides. Obstacles of these nanofluidic pathways are also discussed. In the end of this thesis, a proposal of integration of solid state nanopore and fixed-gap recognition tunneling sequencing technique for a more accurate DNA and peptide readout is discussed, together with some early study work, which gives a new direction for nanopore based sequencing. At the same time, I need to thank all my colleagues who I have the honor to work with in the past, including Dr.
We studied the steady-state and time-resolved luminescence properties of CdTe and CdTe/CdS core/s... more We studied the steady-state and time-resolved luminescence properties of CdTe and CdTe/CdS core/shell quantum dots by one-and two-photon excitation with a femtosecond laser of low intensity. The 800 nm excitation causes a blue shift of the emission peak compared with 400 nm laser excitation. Near-quadratic laser power dependence of the up-conversion intensity and biexponential decay kinetics are observed. It is found that upconversion luminescence is composed of a photoinduced trapping and a band edge excitonic state. The blue shift of the emission peak is caused by the relative change in luminescence intensity between excitonic and trapping states. Two-step two-photon absorption involving the surface as intermediate states has been proposed for the mechanism of up-conversion luminescence of CdTe/CdS quantum dots.
Bioelectronics research has mainly focused on redox-active proteins because of their role in biol... more Bioelectronics research has mainly focused on redox-active proteins because of their role in biological charge transport. In these proteins, electronic conductance is a maximum when electrons are injected at the known redox potential of the protein. It has been shown recently that many non-redox active proteins are good electronic conductors, though the mechanism of conduction is not yet understood. Here, we report single-molecule measurements of the conductance of three non-redox active proteins, maintained under potential control in solution, as a function of electron injection energy. All three proteins show a conductance resonance at a potential ~0.7V removed from the nearest oxidation potential of their constituent amino acids. If this shift reflects a reduction of reorganization energy in the interior of the protein, it would account for the long range conductance observed when carriers are injected into the interior of a protein.
Solid-state nanopores have broad applications in single-molecule biosensing and diagnostics, but ... more Solid-state nanopores have broad applications in single-molecule biosensing and diagnostics, but their high electrical noise associated with a large device capacitance has seriously limited both their sensing accuracy and recording speed. Current strategies to mitigate the noise has focused on introducing insulating materials (such as polymer or glass) to decrease the device capacitance, but the complex process integration schemes diminish the potential to reproducibly create such nanopore devices. Here, we report a scalable and reliable approach to create nanopore membranes on sapphire with triangular shape and controlled dimensions by anisotropic wet etching a crystalline sapphire wafer, thus eliminating the noise-dominating stray capacitance that is intrinsic to conventional Si based devices. We demonstrate tunable control of the membrane dimension in a wide range from ∼200 μm to as small as 5 μm, which corresponds to <1 pF membrane capacitance for a hypothetical 1-2 nm thick ...
Proteins have been shown to be electrically-conductive if tethered to an electrode by means of a ... more Proteins have been shown to be electrically-conductive if tethered to an electrode by means of a specific binding agent, opening the possibility of building electronic devices that exploit the remarkable chemical versatility of enzymes by direct read-out of activity. Single-molecule conductance increases tenfold if two specific contacts are made (as is possible with bivalent antibodies). Here, we address the problem of forming contacts with proteins that, unlike antibodies, do not possess a multiplicity of native binding sites. In particular, we have engineered contact points into a Ф29 polymerase, with the points chosen so as to leave the active site free. Contacts are formed by introducing biotinylatable peptide sequences into Ф29 and functionalizing electrodes with streptavidin. Ф29 connected by one biotinylated contact and one non-specific contact shows rapid small fluctuations in current when activated. Signals are greatly enhanced with two specific contacts, a feature in the c...
Observation of giant conductance fluctuations in a protein To cite this article: Bintian Zhang et... more Observation of giant conductance fluctuations in a protein To cite this article: Bintian Zhang et al 2017 Nano Futures 1 035002 View the article online for updates and enhancements.
Proceedings of the National Academy of Sciences, 2019
Significance The measured electronic properties of proteins are known to depend critically on con... more Significance The measured electronic properties of proteins are known to depend critically on contacts, although little is known at the single-molecule level. Here, we have measured the conductance of single-protein molecules in their natural aqueous environment, but in conditions where no ion current flows, finding large conductances (nanosiemens) over long paths (many nanometers) when the protein is tethered by chemical contacts formed by binding-specific ligands. This provides a method for forming reliable contacts to proteins, and for the specific detection of single molecules. Thus, single antibodies, such as anti-Ebola IgG, can be detected electrically when they bind a peptide epitope tethered to electrodes, with no background signal from molecules that do not bind specifically.
Foremost among the challenges facing single molecule sequencing of proteins by nanopores is the l... more Foremost among the challenges facing single molecule sequencing of proteins by nanopores is the lack of a universal method for driving proteins or peptides into nanopores. In contrast to nucleic acids, the backbones of which are uniformly negatively charged nucleotides, proteins carry positive, negative and neutral side chains that are randomly distributed. Recombinant proteins carrying a negatively charged oligonucleotide or polypeptide at the C-termini can be translocated through a α-hemolysin (α-HL) nanopore, but the required genetic engineering limits the generality of these approaches. In this present study, we have developed a chemical approach for addition of a charged oligomer to peptides so that they can be translocated through nanopores. As an example, an oligonucleotide PolyT20 was tethered to peptides through first selectively functionalizing their N-termini with azide followed by a click reaction. The data show that the peptide-PolyT20 conjugates translocated through nanopores, whereas the unmodified peptides did not. Surprisingly, the conjugates with their peptides tethered at the 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-end of PolyT20 passed the nanopores more rapidly than the PolyT20 alone. The PolyT20 also yielded a wider distribution of blockade currents. The same broad distribution was found for a conjugate with its peptide tethered at the 3&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-end of PolyT20, suggesting that the larger blockades (and longer translocation times) are associated with events in which the 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-end of the PolyT20 enters the pore first.
Energy transfer from water-soluble quantum dots (QDs) to porphyrinlike sensitizers is studied by ... more Energy transfer from water-soluble quantum dots (QDs) to porphyrinlike sensitizers is studied by time-resolved spectroscopy of two-photon excitation with femtosecond laser pulses. Evident transfer results are observed. Electron exchange is found to be the dominant transfer mechanism. Relative intensity change between excitonic and trapping emission implies that nonradiative energy transfer occurs through the trapping state of QDs, which presents a
The human proteome has millions of protein variants due to alternative RNA splicing and posttrans... more The human proteome has millions of protein variants due to alternative RNA splicing and posttranslational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single molecule protein sequencing is a critical step in the search for protein biomarkers. Here we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules and measuring the electron tunneling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic 'fingerprints' associated with each binding motif. With this recognition tunneling technique, we are able to identify D, L enantiomers, a methylated amino acid, isobaric isomers, and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore.
Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as flu... more Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as fluorescence was recorded from charged dye molecules translocating through the SWCNT. Fluorescence bursts generally follow ion current peaks with a delay time consistent with diffusion from the end of the SWCNT to the fluorescence collection point. The fluorescence amplitude distribution of the bursts is consistent with single-molecule signals. Thus each peak in the ion current flowing through the SWCNT is associated with the translocation of a single molecule. Ion current peaks (as opposed to blockades) were produced by both positively (Rhodamine 6G) and negatively (Alexa 546) charged molecules, showing that the charge filtering responsible for the current bursts is caused by the molecules themselves.
The photoluminescence (PL) properties of the guest-host films, using CdTeS/ZnS core shell quantum... more The photoluminescence (PL) properties of the guest-host films, using CdTeS/ZnS core shell quantum dots (QDs) as the guest and organic small-molecule material Alq 3 as the host, are studied by steady-state and time-resolved PL spectroscopy. Both the relative intensity and the PL lifetime are intensively dependent on the weight ratio of Alq 3 and CdTeS/ZnS QDs. The detailed analysis provides clear evidence for a Fo¨rster energy transfer from Alq 3 host to QDs guest, based on the nonradiative resonant transfer mechanism. The results are relevant to the application of hybrid organic/inorganic systems to OLEDs.
Journal of Micro-nanolithography Mems and Moems, 2010
Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interac... more Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interaction between CdSe quantum dots (QDs) and mesotetraphenylporphyrin (TPP) photosensitizers under two-photon excitation with femtosecond laser pulses. The luminescent intensity ...
Nanopores were fabricated with an integrated microscale Pd electrode coated with either a hydroge... more Nanopores were fabricated with an integrated microscale Pd electrode coated with either a hydrogen-bonding or hydrophobic monolayer. Bare pores, or those coated with octanethiol, translocated single-stranded DNA with times of a few microseconds per base. Pores functionalized with 4(5)-(2-mercaptoethyl)-1H-imidazole-2-carboxamide slowed average translocation times, calculated as the duration of the event divided by the number of bases translocated, to about 100 μs per base at biases in the range of 50 to 80 mV.
Previous measurements of the electronic conductance of DNA nucleotides or amino acids have used t... more Previous measurements of the electronic conductance of DNA nucleotides or amino acids have used tunnel junctions in which the gap is mechanically adjusted, such as scanning tunneling microscopes or mechanically controllable break junctions. Fixed-junction devices have, at best, detected the passage of whole DNA molecules without yielding chemical information. Here, we report on a layered tunnel junction in which the tunnel gap is defined by a dielectric layer, deposited by atomic layer deposition. Reactive ion etching is used to drill a hole through the layers so that the tunnel junction can be exposed to molecules in solution. When the metal electrodes are functionalized with recognition molecules that capture DNA nucleotides via hydrogen bonds, the identities of the individual nucleotides are revealed by characteristic features of the fluctuating tunnel current associated with single-molecule binding events.
The human proteome has millions of protein variants due to alternative RNA splicing and posttrans... more The human proteome has millions of protein variants due to alternative RNA splicing and posttranslational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single molecule protein sequencing is a critical step in the search for protein biomarkers. Here we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules and measuring the electron tunneling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic 'fingerprints' associated with each binding motif. With this recognition tunneling technique, we are able to identify D, L enantiomers, a methylated amino acid, isobaric isomers, and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore.
The photoluminescence properties of the blend films consisting of the hole transport and electron... more The photoluminescence properties of the blend films consisting of the hole transport and electron transport materials, PVK and Alq3, are studied by steady-state and time-resolved photoluminescence (PL) spectroscopy. Both the relative intensity and the photoluminescence lifetime are intensively dependent of the weight ratios of PVK and Alq3. The detailed analysis of experiment data provides clear evidence for a Förster energy
Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as flu... more Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as fluorescence was recorded from charged dye molecules translocating through the SWCNT. Fluorescence bursts generally follow ion current peaks with a delay time consistent with diffusion from the end of the SWCNT to the fluorescence collection point. The fluorescence amplitude distribution of the bursts is consistent with single-molecule signals. Thus each peak in the ion current flowing through the SWCNT is associated with the translocation of a single molecule. Ion current peaks (as opposed to blockades) were produced by both positively (Rhodamine 6G) and negatively (Alexa 546) charged molecules, showing that the charge filtering responsible for the current bursts is caused by the molecules themselves.
DNA molecular wires have been studied extensively because of the ease with which molecules of con... more DNA molecular wires have been studied extensively because of the ease with which molecules of controlled length and composition can be synthesized. The same has not been true for proteins. Here, we have synthesized and studied a series of consensus tetratricopeptide repeat (CTPR) proteins, spanning 4 to 20 nm in length, in increments of 4 nm. For lengths in excess of 6 nm, their conductance exceeds that of the canonical molecular wire, oligo(phenylene-ethylenene), because of the more gradual decay of conductance with length in the protein. We show that, while the conductance decay fits an exponential (characteristic of quantum tunneling) and not a linear increase of resistance with length (characteristic of hopping transport), it is also accounted for by a square-law dependence on length (characteristic of weakly driven hopping). Measurements of the energy dependence of the decay length rule out the quantum tunneling case. A resonance in the carrier injection energy shows that allowed states in the protein align with the Fermi energy of the electrodes. Both the energy of these states and the long-range of hopping suggest that the reorganization induced by hole formation is greatly reduced inside the protein. We outline a model for calculating the molecular-electronic properties of proteins.
Driven by the curiosity for the secret of life, the effort on sequencing of DNAs and other large ... more Driven by the curiosity for the secret of life, the effort on sequencing of DNAs and other large biopolymers has never been respited. Advanced from recent sequencing techniques, nanotube and nanopore based sequencing has been attracting much attention. This thesis focuses on the study of first and crucial compartment of the third generation sequencing technique, the capture and translocation of biopolymers, and discuss the advantages and obstacles of two different nanofluidic pathways, nanotubes and nanopores for single molecule capturing and translocation. Carbon nanotubes with its constrained structure, the frictionless inner wall and strong electroosmotic flow, are promising materials for linearly threading DNA and other biopolymers for sequencing. Solid state nanopore on the other hand, is a robust chemical, thermal and mechanical stable nanofluidic device, which has a high capturing rate and, to some extent, good controllable threading ability for DNA and other biomolecules. These two different but similar nanofluidic pathways both provide a good preparation of analyte molecules for the sequencing purpose. In addition, more and more research interests have move onto peptide chains and protein sensing. For proteome is better and more direct indicators for human health, peptide chains and protein sensing have a much wider range of applications on bio-medicine, disease early diagnoses, and etc. A universal peptide chain nanopore sensing technique with universal chemical modification of peptides is discussed in this thesis as well, which unifies the nanopore capturing process for vast varieties of peptides. Obstacles of these nanofluidic pathways are also discussed. In the end of this thesis, a proposal of integration of solid state nanopore and fixed-gap recognition tunneling sequencing technique for a more accurate DNA and peptide readout is discussed, together with some early study work, which gives a new direction for nanopore based sequencing. At the same time, I need to thank all my colleagues who I have the honor to work with in the past, including Dr.
We studied the steady-state and time-resolved luminescence properties of CdTe and CdTe/CdS core/s... more We studied the steady-state and time-resolved luminescence properties of CdTe and CdTe/CdS core/shell quantum dots by one-and two-photon excitation with a femtosecond laser of low intensity. The 800 nm excitation causes a blue shift of the emission peak compared with 400 nm laser excitation. Near-quadratic laser power dependence of the up-conversion intensity and biexponential decay kinetics are observed. It is found that upconversion luminescence is composed of a photoinduced trapping and a band edge excitonic state. The blue shift of the emission peak is caused by the relative change in luminescence intensity between excitonic and trapping states. Two-step two-photon absorption involving the surface as intermediate states has been proposed for the mechanism of up-conversion luminescence of CdTe/CdS quantum dots.
Bioelectronics research has mainly focused on redox-active proteins because of their role in biol... more Bioelectronics research has mainly focused on redox-active proteins because of their role in biological charge transport. In these proteins, electronic conductance is a maximum when electrons are injected at the known redox potential of the protein. It has been shown recently that many non-redox active proteins are good electronic conductors, though the mechanism of conduction is not yet understood. Here, we report single-molecule measurements of the conductance of three non-redox active proteins, maintained under potential control in solution, as a function of electron injection energy. All three proteins show a conductance resonance at a potential ~0.7V removed from the nearest oxidation potential of their constituent amino acids. If this shift reflects a reduction of reorganization energy in the interior of the protein, it would account for the long range conductance observed when carriers are injected into the interior of a protein.
Solid-state nanopores have broad applications in single-molecule biosensing and diagnostics, but ... more Solid-state nanopores have broad applications in single-molecule biosensing and diagnostics, but their high electrical noise associated with a large device capacitance has seriously limited both their sensing accuracy and recording speed. Current strategies to mitigate the noise has focused on introducing insulating materials (such as polymer or glass) to decrease the device capacitance, but the complex process integration schemes diminish the potential to reproducibly create such nanopore devices. Here, we report a scalable and reliable approach to create nanopore membranes on sapphire with triangular shape and controlled dimensions by anisotropic wet etching a crystalline sapphire wafer, thus eliminating the noise-dominating stray capacitance that is intrinsic to conventional Si based devices. We demonstrate tunable control of the membrane dimension in a wide range from ∼200 μm to as small as 5 μm, which corresponds to <1 pF membrane capacitance for a hypothetical 1-2 nm thick ...
Proteins have been shown to be electrically-conductive if tethered to an electrode by means of a ... more Proteins have been shown to be electrically-conductive if tethered to an electrode by means of a specific binding agent, opening the possibility of building electronic devices that exploit the remarkable chemical versatility of enzymes by direct read-out of activity. Single-molecule conductance increases tenfold if two specific contacts are made (as is possible with bivalent antibodies). Here, we address the problem of forming contacts with proteins that, unlike antibodies, do not possess a multiplicity of native binding sites. In particular, we have engineered contact points into a Ф29 polymerase, with the points chosen so as to leave the active site free. Contacts are formed by introducing biotinylatable peptide sequences into Ф29 and functionalizing electrodes with streptavidin. Ф29 connected by one biotinylated contact and one non-specific contact shows rapid small fluctuations in current when activated. Signals are greatly enhanced with two specific contacts, a feature in the c...
Observation of giant conductance fluctuations in a protein To cite this article: Bintian Zhang et... more Observation of giant conductance fluctuations in a protein To cite this article: Bintian Zhang et al 2017 Nano Futures 1 035002 View the article online for updates and enhancements.
Proceedings of the National Academy of Sciences, 2019
Significance The measured electronic properties of proteins are known to depend critically on con... more Significance The measured electronic properties of proteins are known to depend critically on contacts, although little is known at the single-molecule level. Here, we have measured the conductance of single-protein molecules in their natural aqueous environment, but in conditions where no ion current flows, finding large conductances (nanosiemens) over long paths (many nanometers) when the protein is tethered by chemical contacts formed by binding-specific ligands. This provides a method for forming reliable contacts to proteins, and for the specific detection of single molecules. Thus, single antibodies, such as anti-Ebola IgG, can be detected electrically when they bind a peptide epitope tethered to electrodes, with no background signal from molecules that do not bind specifically.
Foremost among the challenges facing single molecule sequencing of proteins by nanopores is the l... more Foremost among the challenges facing single molecule sequencing of proteins by nanopores is the lack of a universal method for driving proteins or peptides into nanopores. In contrast to nucleic acids, the backbones of which are uniformly negatively charged nucleotides, proteins carry positive, negative and neutral side chains that are randomly distributed. Recombinant proteins carrying a negatively charged oligonucleotide or polypeptide at the C-termini can be translocated through a α-hemolysin (α-HL) nanopore, but the required genetic engineering limits the generality of these approaches. In this present study, we have developed a chemical approach for addition of a charged oligomer to peptides so that they can be translocated through nanopores. As an example, an oligonucleotide PolyT20 was tethered to peptides through first selectively functionalizing their N-termini with azide followed by a click reaction. The data show that the peptide-PolyT20 conjugates translocated through nanopores, whereas the unmodified peptides did not. Surprisingly, the conjugates with their peptides tethered at the 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-end of PolyT20 passed the nanopores more rapidly than the PolyT20 alone. The PolyT20 also yielded a wider distribution of blockade currents. The same broad distribution was found for a conjugate with its peptide tethered at the 3&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-end of PolyT20, suggesting that the larger blockades (and longer translocation times) are associated with events in which the 5&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-end of the PolyT20 enters the pore first.
Energy transfer from water-soluble quantum dots (QDs) to porphyrinlike sensitizers is studied by ... more Energy transfer from water-soluble quantum dots (QDs) to porphyrinlike sensitizers is studied by time-resolved spectroscopy of two-photon excitation with femtosecond laser pulses. Evident transfer results are observed. Electron exchange is found to be the dominant transfer mechanism. Relative intensity change between excitonic and trapping emission implies that nonradiative energy transfer occurs through the trapping state of QDs, which presents a
The human proteome has millions of protein variants due to alternative RNA splicing and posttrans... more The human proteome has millions of protein variants due to alternative RNA splicing and posttranslational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single molecule protein sequencing is a critical step in the search for protein biomarkers. Here we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules and measuring the electron tunneling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic 'fingerprints' associated with each binding motif. With this recognition tunneling technique, we are able to identify D, L enantiomers, a methylated amino acid, isobaric isomers, and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore.
Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as flu... more Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as fluorescence was recorded from charged dye molecules translocating through the SWCNT. Fluorescence bursts generally follow ion current peaks with a delay time consistent with diffusion from the end of the SWCNT to the fluorescence collection point. The fluorescence amplitude distribution of the bursts is consistent with single-molecule signals. Thus each peak in the ion current flowing through the SWCNT is associated with the translocation of a single molecule. Ion current peaks (as opposed to blockades) were produced by both positively (Rhodamine 6G) and negatively (Alexa 546) charged molecules, showing that the charge filtering responsible for the current bursts is caused by the molecules themselves.
The photoluminescence (PL) properties of the guest-host films, using CdTeS/ZnS core shell quantum... more The photoluminescence (PL) properties of the guest-host films, using CdTeS/ZnS core shell quantum dots (QDs) as the guest and organic small-molecule material Alq 3 as the host, are studied by steady-state and time-resolved PL spectroscopy. Both the relative intensity and the PL lifetime are intensively dependent on the weight ratio of Alq 3 and CdTeS/ZnS QDs. The detailed analysis provides clear evidence for a Fo¨rster energy transfer from Alq 3 host to QDs guest, based on the nonradiative resonant transfer mechanism. The results are relevant to the application of hybrid organic/inorganic systems to OLEDs.
Journal of Micro-nanolithography Mems and Moems, 2010
Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interac... more Steady-state and nanosecond time-resolved spectroscopies are performed to investigate the interaction between CdSe quantum dots (QDs) and mesotetraphenylporphyrin (TPP) photosensitizers under two-photon excitation with femtosecond laser pulses. The luminescent intensity ...
Nanopores were fabricated with an integrated microscale Pd electrode coated with either a hydroge... more Nanopores were fabricated with an integrated microscale Pd electrode coated with either a hydrogen-bonding or hydrophobic monolayer. Bare pores, or those coated with octanethiol, translocated single-stranded DNA with times of a few microseconds per base. Pores functionalized with 4(5)-(2-mercaptoethyl)-1H-imidazole-2-carboxamide slowed average translocation times, calculated as the duration of the event divided by the number of bases translocated, to about 100 μs per base at biases in the range of 50 to 80 mV.
Previous measurements of the electronic conductance of DNA nucleotides or amino acids have used t... more Previous measurements of the electronic conductance of DNA nucleotides or amino acids have used tunnel junctions in which the gap is mechanically adjusted, such as scanning tunneling microscopes or mechanically controllable break junctions. Fixed-junction devices have, at best, detected the passage of whole DNA molecules without yielding chemical information. Here, we report on a layered tunnel junction in which the tunnel gap is defined by a dielectric layer, deposited by atomic layer deposition. Reactive ion etching is used to drill a hole through the layers so that the tunnel junction can be exposed to molecules in solution. When the metal electrodes are functionalized with recognition molecules that capture DNA nucleotides via hydrogen bonds, the identities of the individual nucleotides are revealed by characteristic features of the fluctuating tunnel current associated with single-molecule binding events.
The human proteome has millions of protein variants due to alternative RNA splicing and posttrans... more The human proteome has millions of protein variants due to alternative RNA splicing and posttranslational modifications, and variants that are related to diseases are frequently present in minute concentrations. For DNA and RNA, low concentrations can be amplified using the polymerase chain reaction, but there is no such reaction for proteins. Therefore, the development of single molecule protein sequencing is a critical step in the search for protein biomarkers. Here we show that single amino acids can be identified by trapping the molecules between two electrodes that are coated with a layer of recognition molecules and measuring the electron tunneling current across the junction. A given molecule can bind in more than one way in the junction, and we therefore use a machine-learning algorithm to distinguish between the sets of electronic 'fingerprints' associated with each binding motif. With this recognition tunneling technique, we are able to identify D, L enantiomers, a methylated amino acid, isobaric isomers, and short peptides. The results suggest that direct electronic sequencing of single proteins could be possible by sequentially measuring the products of processive exopeptidase digestion, or by using a molecular motor to pull proteins through a tunnel junction integrated with a nanopore.
The photoluminescence properties of the blend films consisting of the hole transport and electron... more The photoluminescence properties of the blend films consisting of the hole transport and electron transport materials, PVK and Alq3, are studied by steady-state and time-resolved photoluminescence (PL) spectroscopy. Both the relative intensity and the photoluminescence lifetime are intensively dependent of the weight ratios of PVK and Alq3. The detailed analysis of experiment data provides clear evidence for a Förster energy
Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as flu... more Ion current through a single-walled carbon nanotube (SWCNT) was monitored at the same time as fluorescence was recorded from charged dye molecules translocating through the SWCNT. Fluorescence bursts generally follow ion current peaks with a delay time consistent with diffusion from the end of the SWCNT to the fluorescence collection point. The fluorescence amplitude distribution of the bursts is consistent with single-molecule signals. Thus each peak in the ion current flowing through the SWCNT is associated with the translocation of a single molecule. Ion current peaks (as opposed to blockades) were produced by both positively (Rhodamine 6G) and negatively (Alexa 546) charged molecules, showing that the charge filtering responsible for the current bursts is caused by the molecules themselves.
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