1
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Raja SN, Jain S, Kipen J, Jaldén J, Stemme G, Herland A, Niklaus F. Electromigrated Gold Nanogap Tunnel Junction Arrays: Fabrication and Electrical Behavior in Liquid and Gaseous Media. ACS APPLIED MATERIALS & INTERFACES 2024; 16:37131-37146. [PMID: 38954436 PMCID: PMC11261569 DOI: 10.1021/acsami.4c03282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 06/19/2024] [Accepted: 06/19/2024] [Indexed: 07/04/2024]
Abstract
Tunnel junctions have been suggested as high-throughput electronic single molecule sensors in liquids with several seminal experiments conducted using break junctions with reconfigurable gaps. For practical single molecule sensing applications, arrays of on-chip integrated fixed-gap tunnel junctions that can be built into compact systems are preferable. Fabricating nanogaps by electromigration is one of the most promising approaches to realize on-chip integrated tunnel junction sensors. However, the electrical behavior of fixed-gap tunnel junctions immersed in liquid media has not been systematically studied to date, and the formation of electromigrated nanogap tunnel junctions in liquid media has not yet been demonstrated. In this work, we perform a comparative study of the formation and electrical behavior of arrays of gold nanogap tunnel junctions made by feedback-controlled electromigration immersed in various liquid and gaseous media (deionized water, mesitylene, ethanol, nitrogen, and air). We demonstrate that tunnel junctions can be obtained from microfabricated gold nanoconstrictions inside liquid media. Electromigration of junctions in air produces the highest yield (61-67%), electromigration in deionized water and mesitylene results in a lower yield than in air (44-48%), whereas electromigration in ethanol fails to produce viable tunnel junctions due to interfering electrochemical processes. We map out the stability of the conductance characteristics of the resulting tunnel junctions and identify medium-specific operational conditions that have an impact on the yield of forming stable junctions. Furthermore, we highlight the unique challenges associated with working with arrays of large numbers of tunnel junctions in batches. Our findings will inform future efforts to build single molecule sensors using on-chip integrated tunnel junctions.
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Affiliation(s)
- Shyamprasad N. Raja
- Division
of Micro and Nanosystems (MST), School of Electrical Engineering and
Computer Science (EECS), KTH Royal Institute
of Technology, SE-10044 Stockholm, Sweden
| | - Saumey Jain
- Division
of Micro and Nanosystems (MST), School of Electrical Engineering and
Computer Science (EECS), KTH Royal Institute
of Technology, SE-10044 Stockholm, Sweden
- Division
of Nanobiotechnology, SciLifeLab, Department of Protein Science, School
of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
| | - Javier Kipen
- Division
of Information Science and Engineering (ISE), School of Electrical
Engineering and Computer Science (EECS), KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
| | - Joakim Jaldén
- Division
of Information Science and Engineering (ISE), School of Electrical
Engineering and Computer Science (EECS), KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
| | - Göran Stemme
- Division
of Micro and Nanosystems (MST), School of Electrical Engineering and
Computer Science (EECS), KTH Royal Institute
of Technology, SE-10044 Stockholm, Sweden
| | - Anna Herland
- Division
of Nanobiotechnology, SciLifeLab, Department of Protein Science, School
of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden
- AIMES-Center
for the Advancement of Integrated Medical and Engineering Sciences,
Department of Neuroscience, Karolinska Institute, SE-17177 Solna, Sweden
| | - Frank Niklaus
- Division
of Micro and Nanosystems (MST), School of Electrical Engineering and
Computer Science (EECS), KTH Royal Institute
of Technology, SE-10044 Stockholm, Sweden
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2
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Ju H, Cheng L, Li M, Mei K, He S, Jia C, Guo X. Single-Molecule Electrical Profiling of Peptides and Proteins. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024; 11:e2401877. [PMID: 38639403 PMCID: PMC11267281 DOI: 10.1002/advs.202401877] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Revised: 04/03/2024] [Indexed: 04/20/2024]
Abstract
In recent decades, there has been a significant increase in the application of single-molecule electrical analysis platforms in studying proteins and peptides. These advanced analysis methods have the potential for deep investigation of enzymatic working mechanisms and accurate monitoring of dynamic changes in protein configurations, which are often challenging to achieve in ensemble measurements. In this work, the prominent research progress in peptide and protein-related studies are surveyed using electronic devices with single-molecule/single-event sensitivity, including single-molecule junctions, single-molecule field-effect transistors, and nanopores. In particular, the successful commercial application of nanopores in DNA sequencing has made it one of the most promising techniques in protein sequencing at the single-molecule level. From single peptides to protein complexes, the correlation between their electrical characteristics, structures, and biological functions is gradually being established. This enables to distinguish different molecular configurations of these biomacromolecules through real-time electrical monitoring of their life activities, significantly improving the understanding of the mechanisms underlying various life processes.
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Affiliation(s)
- Hongyu Ju
- School of Pharmaceutical Science and TechnologyTianjin UniversityTianjin300072P. R. China
- Center of Single‐Molecule SciencesInstitute of Modern OpticsFrontiers Science Center for New Organic MatterTianjin Key Laboratory of Microscale Optical Information Science and TechnologyCollege of Electronic Information and Optical EngineeringNankai UniversityTianjin300350P. R. China
| | - Li Cheng
- Center of Single‐Molecule SciencesInstitute of Modern OpticsFrontiers Science Center for New Organic MatterTianjin Key Laboratory of Microscale Optical Information Science and TechnologyCollege of Electronic Information and Optical EngineeringNankai UniversityTianjin300350P. R. China
| | - Mengmeng Li
- Center of Single‐Molecule SciencesInstitute of Modern OpticsFrontiers Science Center for New Organic MatterTianjin Key Laboratory of Microscale Optical Information Science and TechnologyCollege of Electronic Information and Optical EngineeringNankai UniversityTianjin300350P. R. China
| | - Kunrong Mei
- School of Pharmaceutical Science and TechnologyTianjin UniversityTianjin300072P. R. China
| | - Suhang He
- Center of Single‐Molecule SciencesInstitute of Modern OpticsFrontiers Science Center for New Organic MatterTianjin Key Laboratory of Microscale Optical Information Science and TechnologyCollege of Electronic Information and Optical EngineeringNankai UniversityTianjin300350P. R. China
| | - Chuancheng Jia
- Center of Single‐Molecule SciencesInstitute of Modern OpticsFrontiers Science Center for New Organic MatterTianjin Key Laboratory of Microscale Optical Information Science and TechnologyCollege of Electronic Information and Optical EngineeringNankai UniversityTianjin300350P. R. China
| | - Xuefeng Guo
- Center of Single‐Molecule SciencesInstitute of Modern OpticsFrontiers Science Center for New Organic MatterTianjin Key Laboratory of Microscale Optical Information Science and TechnologyCollege of Electronic Information and Optical EngineeringNankai UniversityTianjin300350P. R. China
- Beijing National Laboratory for Molecular SciencesNational Biomedical Imaging CenterCollege of Chemistry and Molecular EngineeringPeking UniversityBeijing100871P. R. China
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3
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Raja SN, Jain S, Kipen J, Jaldén J, Stemme G, Herland A, Niklaus F. High-bandwidth low-current measurement system for automated and scalable probing of tunnel junctions in liquids. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:074710. [PMID: 39037302 DOI: 10.1063/5.0204188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Accepted: 07/06/2024] [Indexed: 07/23/2024]
Abstract
Tunnel junctions have long been used to immobilize and study the electronic transport properties of single molecules. The sensitivity of tunneling currents to entities in the tunneling gap has generated interest in developing electronic biosensors with single molecule resolution. Tunnel junctions can, for example, be used for sensing bound or unbound DNA, RNA, amino acids, and proteins in liquids. However, manufacturing technologies for on-chip integrated arrays of tunnel junction sensors are still in their infancy, and scalable measurement strategies that allow the measurement of large numbers of tunneling junctions are required to facilitate progress. Here, we describe an experimental setup to perform scalable, high-bandwidth (>10 kHz) measurements of low currents (pA-nA) in arrays of on-chip integrated tunnel junctions immersed in various liquid media. Leveraging a commercially available compact 100 kHz bandwidth low-current measurement instrument, we developed a custom two-terminal probe on which the amplifier is directly mounted to decrease parasitic probe capacitances to sub-pF levels. We also integrated a motorized three-axis stage, which could be powered down using software control, inside the Faraday cage of the setup. This enabled automated data acquisition on arrays of tunnel junctions without worsening the noise floor despite being inside the Faraday cage. A deliberately positioned air gap in the fluidic path ensured liquid perfusion to the chip from outside the Faraday cage without coupling in additional noise. We demonstrate the performance of our setup using rapid current switching observed in electromigrated gold tunnel junctions immersed in deionized water.
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Affiliation(s)
- Shyamprasad N Raja
- Division of Micro and Nanosystems, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Saumey Jain
- Division of Micro and Nanosystems, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
- Division of Nanobiotechnology, SciLife Lab, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Javier Kipen
- Division of Information Science and Engineering, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Joakim Jaldén
- Division of Information Science and Engineering, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Göran Stemme
- Division of Micro and Nanosystems, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
| | - Anna Herland
- Division of Nanobiotechnology, SciLife Lab, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
- AIMES-Center for the Advancement of Integrated Medical and Engineering Sciences, Department of Neuroscience, Karolinska Institute, SE-171 77 Solna, Sweden
| | - Frank Niklaus
- Division of Micro and Nanosystems, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden
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4
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Guo J, Chen PK, Chang S. Molecular-Scale Electronics: From Individual Molecule Detection to the Application of Recognition Sensing. Anal Chem 2024; 96:9303-9316. [PMID: 38809941 DOI: 10.1021/acs.analchem.3c04656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2024]
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5
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López-Ortiz M, Zamora RA, Giannotti MI, Gorostiza P. The Protein Matrix of Plastocyanin Supports Long-Distance Charge Transport with Photosystem I and the Copper Ion Regulates Its Spatial Span and Conductance. ACS NANO 2023; 17:20334-20344. [PMID: 37797170 DOI: 10.1021/acsnano.3c06390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/07/2023]
Abstract
Charge exchange is the fundamental process that sustains cellular respiration and photosynthesis by shuttling electrons in a cascade of electron transfer (ET) steps between redox cofactors. While intraprotein charge exchange is well characterized in protein complexes bearing multiple redox sites, interprotein processes are less understood due to the lack of suitable experimental approaches and the dynamic nature of the interactions. Proteins constrained between electrodes are known to support electron transport (ETp) through the protein matrix even without redox cofactors, as the charges housed by the redox sites in ET are furnished by the electrodes. However, it is unknown whether protein ETp mechanisms apply to the interprotein medium present under physiological conditions. We study interprotein charge exchange between plant photosystem I (PSI) and its soluble redox partner plastocyanin (Pc) and address the role of the Pc copper center. Using electrochemical scanning tunneling spectroscopy (ECSTS) current-distance and blinking measurements, we quantify the spatial span of charge exchange between individual Pc/PSI pairs and ETp through transient Pc/PSI complexes. Pc devoid of the redox center (Pcapo) can exchange charge with PSI at longer distances than with the copper ion (Pcholo). Conductance bursts associated with Pcapo/PSI complex formation are higher than in Pcholo/PSI. Thus, copper ions are not required for long-distance Pc/PSI ETp but regulate its spatial span and conductance. Our results suggest that the redox center that carries the charge in Pc is not necessary to exchange it in interprotein ET through the aqueous solution and question the canonical view of tight complex binding between redox protein partners.
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Affiliation(s)
- Manuel López-Ortiz
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology, Baldiri Reixac 10-12, Barcelona 08028, Spain
- CIBER-BBN, ISCIII, Barcelona 08028, Spain
| | - Ricardo A Zamora
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology, Baldiri Reixac 10-12, Barcelona 08028, Spain
- CIBER-BBN, ISCIII, Barcelona 08028, Spain
| | - Marina I Giannotti
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology, Baldiri Reixac 10-12, Barcelona 08028, Spain
- CIBER-BBN, ISCIII, Barcelona 08028, Spain
- Department of Materials Science and Physical Chemistry, University of Barcelona, Martí i Franquès 1-11, Barcelona 08028, Spain
| | - Pau Gorostiza
- Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology, Baldiri Reixac 10-12, Barcelona 08028, Spain
- CIBER-BBN, ISCIII, Barcelona 08028, Spain
- Catalan Institution for Research and Advanced Studies (ICREA), Barcelona 08010, Spain
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6
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Afsari S, Mukherjee S, Halloran N, Ghirlanda G, Ryan E, Wang X, Lindsay S. Heavy Water Reduces the Electronic Conductance of Protein Wires via Deuteron Interactions with Aromatic Residues. NANO LETTERS 2023; 23:8907-8913. [PMID: 37772726 PMCID: PMC11177565 DOI: 10.1021/acs.nanolett.3c02263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/30/2023]
Abstract
Proteins are versatile, self-assembling nanoelectronic components, but their hopping conductivity is expected to be influenced by solvent fluctuations. The role of the solvent was investigated by measuring the single molecule conductance of several proteins in both H2O and D2O. The conductance of a homologous series of protein wires decreases more rapidly with length in D2O, indicating a 6-fold decrease in carrier diffusion constant relative to the same protein in H2O. The effect was found to depend on the specific aromatic amino acid composition. A tryptophan zipper protein showed a decrease in conductance similar to that of the protein wires, whereas a phenylalanine zipper protein was insensitive to solvent changes. Tryptophan contains an indole amine, whereas the phenylalanine aromatic ring has no exchangeable protons, so the effect of heavy water on conductance is a consequence of specific D- or H-interactions with the aromatic residues.
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Affiliation(s)
- Sepideh Afsari
- Biodesign Institute, Arizona State University, Tempe, AZ 85287
| | - Sohini Mukherjee
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287
| | - Nicholas Halloran
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287
| | | | - Eathen Ryan
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287
| | - Xu Wang
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287
| | - Stuart Lindsay
- Biodesign Institute, Arizona State University, Tempe, AZ 85287
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287
- Department of Physics, Arizona State University, Tempe, AZ 85287
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7
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Jiang T, Zeng BF, Zhang B, Tang L. Single-molecular protein-based bioelectronics via electronic transport: fundamentals, devices and applications. Chem Soc Rev 2023; 52:5968-6002. [PMID: 37498342 DOI: 10.1039/d2cs00519k] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/28/2023]
Abstract
Biomolecular electronics is a rapidly growing multidisciplinary field that combines biology, nanoscience, and engineering to bridge the two important fields of life sciences and molecular electronics. Proteins are remarkable for their ability to recognize molecules and transport electrons, making the integration of proteins into electronic devices a long sought-after goal and leading to the emergence of the field of protein-based bioelectronics, also known as proteotronics. This field seeks to design and create new biomolecular electronic platforms that allow for the understanding and manipulation of protein-mediated electronic charge transport and related functional applications. In recent decades, there have been numerous reports on protein-based bioelectronics using a variety of nano-gapped electrical devices and techniques at the single molecular level, which are not achievable with conventional ensemble approaches. This review focuses on recent advances in physical electron transport mechanisms, device fabrication methodologies, and various applications in protein-based bioelectronics. We discuss the most recent progress of the single or few protein-bridged electrical junction fabrication strategies, summarise the work on fundamental and functional applications of protein bioelectronics that enable high and dynamic electron transport, and highlight future perspectives and challenges that still need to be addressed. We believe that this specific review will stimulate the interdisciplinary research of topics related to protein-related bioelectronics, and open up new possibilities for single-molecule biophysics and biomedicine.
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Affiliation(s)
- Tao Jiang
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Biao-Feng Zeng
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China.
| | - Bintian Zhang
- Shenzhen Key Laboratory of Precision Measurement and Early Warning Technology for Urban Environmental Health Risks, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
| | - Longhua Tang
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China.
- Institute of Quantum Sensing, Interdisciplinary Centre for Quantum Information, Zhejiang University, Hangzhou 310027, China
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8
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Jiang T, Yi L, Liu X, Ivanov AP, Edel JB, Tang L. Fabrication of electron tunneling probes for measuring single-protein conductance. Nat Protoc 2023; 18:2579-2599. [PMID: 37420088 DOI: 10.1038/s41596-023-00846-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 04/21/2023] [Indexed: 07/09/2023]
Abstract
Studying the electrical properties of individual proteins is a prominent research area in the field of bioelectronics. Electron tunnelling or quantum mechanical tunnelling (QMT) probes can act as powerful tools for investigating the electrical properties of proteins. However, current fabrication methods for these probes often have limited reproducibility, unreliable contact or inadequate binding of proteins onto the electrodes, so better solutions are required. Here, we detail a generalizable and straightforward set of instructions for fabricating simple, nanopipette-based, tunnelling probes, suitable for measuring conductance in single proteins. Our QMT probe is based on a high-aspect-ratio dual-channel nanopipette that integrates a pair of gold tunneling electrodes with a gap of less than 5 nm, fabricated via the pyrolytic deposition of carbon followed by the electrochemical deposition of gold. The gold tunneling electrodes can be functionalized using an extensive library of available surface modifications to achieve single-protein-electrode contact. We use a biotinylated thiol modification, in which a biotin-streptavidin-biotin bridge is used to form the single-protein junction. The resulting protein-coupled QMT probes enable the stable electrical measurement of the same single protein in solution for up to several hours. We also describe the analysis method used to interpret time-dependent single-protein conductance measurements, which can provide essential information for understanding electron transport and exploring protein dynamics. The total time required to complete the protocol is ~33 h and it can be carried out by users trained in less than 24 h.
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Affiliation(s)
- Tao Jiang
- State Key Laboratory of Modern Optical Instrumentation, Institute of Quantum Sensing, Interdisciplinary Centre for Quantum Information, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou, China
| | - Long Yi
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, London, UK
| | - Xu Liu
- State Key Laboratory of Modern Optical Instrumentation, Institute of Quantum Sensing, Interdisciplinary Centre for Quantum Information, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou, China
| | - Aleksandar P Ivanov
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, London, UK
| | - Joshua B Edel
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, London, UK
| | - Longhua Tang
- State Key Laboratory of Modern Optical Instrumentation, Institute of Quantum Sensing, Interdisciplinary Centre for Quantum Information, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou, China.
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9
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Dief EM, Low PJ, Díez-Pérez I, Darwish N. Advances in single-molecule junctions as tools for chemical and biochemical analysis. Nat Chem 2023; 15:600-614. [PMID: 37106094 DOI: 10.1038/s41557-023-01178-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 03/02/2023] [Indexed: 04/29/2023]
Abstract
The development of miniaturized electronics has led to the design and construction of powerful experimental platforms capable of measuring electronic properties to the level of single molecules, along with new theoretical concepts to aid in the interpretation of the data. A new area of activity is now emerging concerned with repurposing the tools of molecular electronics for applications in chemical and biological analysis. Single-molecule junction techniques, such as the scanning tunnelling microscope break junction and related single-molecule circuit approaches have a remarkable capacity to transduce chemical information from individual molecules, sampled in real time, to electrical signals. In this Review, we discuss single-molecule junction approaches as emerging analytical tools for the chemical and biological sciences. We demonstrate how these analytical techniques are being extended to systems capable of probing chemical reaction mechanisms. We also examine how molecular junctions enable the detection of RNA, DNA, and traces of proteins in solution with limits of detection at the zeptomole level.
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Affiliation(s)
- Essam M Dief
- School of Molecular and Life Sciences, Curtin University, Bentley, Western Australia, Australia
| | - Paul J Low
- School of Molecular Sciences, University of Western Australia, Crawley, Western Australia, Australia
| | - Ismael Díez-Pérez
- Department of Chemistry, Faculty of Natural & Mathematical Sciences, King's College London, London, UK
| | - Nadim Darwish
- School of Molecular and Life Sciences, Curtin University, Bentley, Western Australia, Australia.
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Bera S, Govinda S, Fereiro JA, Pecht I, Sheves M, Cahen D. Biotin Binding Hardly Affects Electron Transport Efficiency across Streptavidin Solid-State Junctions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:1394-1403. [PMID: 36648410 PMCID: PMC9893813 DOI: 10.1021/acs.langmuir.2c02378] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 12/29/2022] [Indexed: 05/27/2023]
Abstract
The electron transport (ETp) efficiency of solid-state protein-mediated junctions is highly influenced by the presence of electron-rich organic cofactors or transition metal ions. Hence, we chose to investigate an interesting cofactor-free non-redox protein, streptavidin (STV), which has unmatched strong binding affinity for an organic small-molecule ligand, biotin, which lacks any electron-rich features. We describe for the first time meso-scale ETp via electrical junctions of STV monolayers and focus on the question of whether the rate of ETp across both native and thiolated STV monolayers is influenced by ligand binding, a process that we show to cause some structural conformation changes in the STV monolayers. Au nanowire-electrode-protein monolayer-microelectrode junctions, fabricated by modifying an earlier procedure to improve the yields of usable junctions, were employed for ETp measurements. Our results on compactly integrated, dense, uniform, ∼3 nm thick STV monolayers indicate that, notwithstanding the slight structural changes in the STV monolayers upon biotin binding, there is no statistically significant conductance change between the free STV and that bound to biotin. The ETp temperature (T) dependence over the 80-300 K range is very small but with an unusual, slightly negative (metallic-like) dependence toward room temperature. Such dependence can be accounted for by the reversible structural shrinkage of the STV at temperatures below 160 K.
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Affiliation(s)
- Sudipta Bera
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Sharada Govinda
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Jerry A. Fereiro
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
- The
School of Chemistry, Indian Institute of
Science Education and Research, Thiruvananthapuram, Maruthamala, Kerala 695551, India
| | - Israel Pecht
- Department
of Immunology and Regenerative Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Mordechai Sheves
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - David Cahen
- Department
of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
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11
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Tang L, Yi L, Jiang T, Ren R, Paulose Nadappuram B, Zhang B, Wu J, Liu X, Lindsay S, Edel JB, Ivanov AP. Measuring conductance switching in single proteins using quantum tunneling. SCIENCE ADVANCES 2022; 8:eabm8149. [PMID: 35584212 PMCID: PMC9116604 DOI: 10.1126/sciadv.abm8149] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Interpreting the electrical signatures of single proteins in electronic junctions has facilitated a better understanding of the intrinsic properties of proteins that are fundamental to chemical and biological processes. Often, this information is not accessible using ensemble and even single-molecule approaches. In addition, the fabrication of nanoscale single-protein junctions remains challenging as they often require sophisticated methods. We report on the fabrication of tunneling probes, direct measurement, and active control (switching) of single-protein conductance with an external field in solution. The probes allowed us to bridge a single streptavidin molecule to two independently addressable, biotin-terminated electrodes and measure single-protein tunneling response over long periods. We show that charge transport through the protein has multiple conductive pathways that depend on the magnitude of the applied bias. These findings open the door for the reliable fabrication of protein-based junctions and can enable their use in future protein-embedded bioelectronics applications.
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Affiliation(s)
- Longhua Tang
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou 310027, China
- Innovation Institute for Artificial Intelligence in Medicine, Zhejiang-California International NanoSystems Institute, Zhejiang University, Hangzhou 310000, China
- Corresponding author. (L.T.); (A.P.I.); (J.B.E.)
| | - Long Yi
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, White City Campus, 82 Wood Lane, London W12 0BZ, UK
| | - Tao Jiang
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou 310027, China
| | - Ren Ren
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, White City Campus, 82 Wood Lane, London W12 0BZ, UK
| | - Binoy Paulose Nadappuram
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, White City Campus, 82 Wood Lane, London W12 0BZ, UK
- Department of Pure and Applied Chemistry, University of Strathclyde, Technology and Innovation Centre, 99 George Street, Glasgow G1 1RD, UK
| | - Bintian Zhang
- Biodesign Institute; School of Life Sciences; Department of Physics; School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Jian Wu
- Innovation Institute for Artificial Intelligence in Medicine, Zhejiang-California International NanoSystems Institute, Zhejiang University, Hangzhou 310000, China
| | - Xu Liu
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, International Research Center for Advanced Photonics, Zhejiang University, Hangzhou 310027, China
| | - Stuart Lindsay
- Biodesign Institute; School of Life Sciences; Department of Physics; School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Joshua B. Edel
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, White City Campus, 82 Wood Lane, London W12 0BZ, UK
- Corresponding author. (L.T.); (A.P.I.); (J.B.E.)
| | - Aleksandar P. Ivanov
- Department of Chemistry, Molecular Science Research Hub, Imperial College London, White City Campus, 82 Wood Lane, London W12 0BZ, UK
- Corresponding author. (L.T.); (A.P.I.); (J.B.E.)
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Molecular electronics sensors on a scalable semiconductor chip: A platform for single-molecule measurement of binding kinetics and enzyme activity. Proc Natl Acad Sci U S A 2022; 119:2112812119. [PMID: 35074874 PMCID: PMC8812571 DOI: 10.1073/pnas.2112812119] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/23/2021] [Indexed: 12/26/2022] Open
Abstract
Detection of molecular interactions is the foundation for many important biotechnology applications in society and industry, such as drug discovery, diagnostics, and DNA sequencing. This report describes a broadly applicable platform for detecting molecular interactions at the single-molecule scale, in real-time, label-free, and potentially highly multiplexable fashion, using single-molecule sensors on a highly scalable semiconductor sensor array chip. Such chips are both practically manufacturable in the near term, and have a durable long-term scaling roadmap, thus providing an ideal way to bring the power of modern chip technology to the broad area of biosensing. This work also realizes a 50-year-old scientific vision of integrating single molecules into electronic chips to achieve the ultimate miniaturization of electronics. For nearly 50 years, the vision of using single molecules in circuits has been seen as providing the ultimate miniaturization of electronic chips. An advanced example of such a molecular electronics chip is presented here, with the important distinction that the molecular circuit elements play the role of general-purpose single-molecule sensors. The device consists of a semiconductor chip with a scalable array architecture. Each array element contains a synthetic molecular wire assembled to span nanoelectrodes in a current monitoring circuit. A central conjugation site is used to attach a single probe molecule that defines the target of the sensor. The chip digitizes the resulting picoamp-scale current-versus-time readout from each sensor element of the array at a rate of 1,000 frames per second. This provides detailed electrical signatures of the single-molecule interactions between the probe and targets present in a solution-phase test sample. This platform is used to measure the interaction kinetics of single molecules, without the use of labels, in a massively parallel fashion. To demonstrate broad applicability, examples are shown for probe molecule binding, including DNA oligos, aptamers, antibodies, and antigens, and the activity of enzymes relevant to diagnostics and sequencing, including a CRISPR/Cas enzyme binding a target DNA, and a DNA polymerase enzyme incorporating nucleotides as it copies a DNA template. All of these applications are accomplished with high sensitivity and resolution, on a manufacturable, scalable, all-electronic semiconductor chip device, thereby bringing the power of modern chips to these diverse areas of biosensing.
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13
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Zhang B, Ryan E, Wang X, Song W, Lindsay S. Electronic Transport in Molecular Wires of Precisely Controlled Length Built from Modular Proteins. ACS NANO 2022; 16:1671-1680. [PMID: 35029115 PMCID: PMC9279515 DOI: 10.1021/acsnano.1c10830] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
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.
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Affiliation(s)
- Bintian Zhang
- Biodesign Institute, Arizona State University, Tempe, AZ 85281
| | - Eathen Ryan
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85281
| | - Xu Wang
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85281
| | - Weisi Song
- Biodesign Institute, Arizona State University, Tempe, AZ 85281
| | - Stuart Lindsay
- Biodesign Institute, Arizona State University, Tempe, AZ 85281
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85281
- Department of Physics, Arizona State University, Tempe, AZ 85281
- Corresponding Author: Stuart Lindsay: Phone 480 205 6432
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14
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Zhang B, Ryan E, Wang X, Lindsay S. Probing Bioelectronic Connections Using Streptavidin Molecules with Modified Valency. J Am Chem Soc 2021; 143:15139-15144. [PMID: 34499834 PMCID: PMC8458255 DOI: 10.1021/jacs.1c05569] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
As molecular electronic components, proteins are distinguished by a remarkably long electronic decay length (∼10 nm) together with high contact resistance and extreme sensitivity to the chemical details of the contact. As a consequence, the conductance of even a large bioelectronic assembly is largely controlled by the conductance of the contacts. Streptavidin is a versatile linker protein that can tether together biotinylated electrodes and biotinylated proteins but with an ambiguity about the contact geometry that arises from its four possible binding sites for biotin. Here, we use engineered streptavidin tetramers, selected to contain a defined ratio of active monomers to "dead" monomers so as to define the biotin binding sites. We find a strong dependence of conductance on the separation of the biotin molecules, consistent with a short-range tunneling interaction within the streptavidin and in contrast to the long-range transport observed inside larger proteins. Hexaglutamate tails label the active monomers, and the additional negative charge enhances conductance significantly. This effect is quantitatively accounted for by an electronic resonance in the protein conductance.
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Affiliation(s)
- Bintian Zhang
- Biodesign Institute, Arizona State University, Tempe AZ 87287, USA
| | - Eathen Ryan
- School of Molecular Sciences, Arizona State University, Tempe AZ 87287, USA
| | - Xu Wang
- School of Molecular Sciences, Arizona State University, Tempe AZ 87287, USA
| | - Stuart Lindsay
- Biodesign Institute, Arizona State University, Tempe AZ 87287, USA
- School of Molecular Sciences, Arizona State University, Tempe AZ 87287, USA
- Department of Physics, Arizona State University, Tempe AZ 87287, USA
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15
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Alfaro JA, Bohländer P, Dai M, Filius M, Howard CJ, van Kooten XF, Ohayon S, Pomorski A, Schmid S, Aksimentiev A, Anslyn EV, Bedran G, Cao C, Chinappi M, Coyaud E, Dekker C, Dittmar G, Drachman N, Eelkema R, Goodlett D, Hentz S, Kalathiya U, Kelleher NL, Kelly RT, Kelman Z, Kim SH, Kuster B, Rodriguez-Larrea D, Lindsay S, Maglia G, Marcotte EM, Marino JP, Masselon C, Mayer M, Samaras P, Sarthak K, Sepiashvili L, Stein D, Wanunu M, Wilhelm M, Yin P, Meller A, Joo C. The emerging landscape of single-molecule protein sequencing technologies. Nat Methods 2021; 18:604-617. [PMID: 34099939 PMCID: PMC8223677 DOI: 10.1038/s41592-021-01143-1] [Citation(s) in RCA: 163] [Impact Index Per Article: 54.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 04/02/2021] [Indexed: 02/04/2023]
Abstract
Single-cell profiling methods have had a profound impact on the understanding of cellular heterogeneity. While genomes and transcriptomes can be explored at the single-cell level, single-cell profiling of proteomes is not yet established. Here we describe new single-molecule protein sequencing and identification technologies alongside innovations in mass spectrometry that will eventually enable broad sequence coverage in single-cell profiling. These technologies will in turn facilitate biological discovery and open new avenues for ultrasensitive disease diagnostics.
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Affiliation(s)
- Javier Antonio Alfaro
- International Centre for Cancer Vaccine Science, University of Gdańsk, Gdańsk, Poland.
| | - Peggy Bohländer
- Faculty of Applied Sciences, Delft University of Technology, Delft, the Netherlands
| | - Mingjie Dai
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Mike Filius
- Department of BioNanoScience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - Cecil J Howard
- Department of Chemistry, University of Texas at Austin, Austin, TX, USA
| | - Xander F van Kooten
- Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel
| | - Shilo Ohayon
- Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel
| | - Adam Pomorski
- Department of BioNanoScience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - Sonja Schmid
- NanoDynamicsLab, Laboratory of Biophysics, Wageningen University, Wageningen, the Netherlands
| | - Aleksei Aksimentiev
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Eric V Anslyn
- Department of Chemistry, University of Texas at Austin, Austin, TX, USA
| | - Georges Bedran
- International Centre for Cancer Vaccine Science, University of Gdańsk, Gdańsk, Poland
| | - Chan Cao
- Institute of Bioengineering, School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Mauro Chinappi
- Dipartimento di Ingegneria Industriale, Università di Roma Tor Vergata, Rome, Italy
| | - Etienne Coyaud
- Univ. Lille, Inserm, CHU Lille, U1192-Protéomique Réponse Inflammatoire Spectrométrie de Masse-PRISM, Lille, France
| | - Cees Dekker
- Department of BioNanoScience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - Gunnar Dittmar
- Department of Infection and Immunity, Luxembourg Institute of Health, Strassen, Luxembourg
- Department of Life Sciences and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | | | - Rienk Eelkema
- Faculty of Applied Sciences, Delft University of Technology, Delft, the Netherlands
| | - David Goodlett
- International Centre for Cancer Vaccine Science, University of Gdańsk, Gdańsk, Poland
- Genome BC Proteomics Centre, University of Victoria, Victoria, British Columbia, Canada
| | | | - Umesh Kalathiya
- International Centre for Cancer Vaccine Science, University of Gdańsk, Gdańsk, Poland
| | - Neil L Kelleher
- Departments of Chemistry and Molecular Biosciences, and the Feinberg School of Medicine, Northwestern University, Evanston, IL, USA
| | - Ryan T Kelly
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT, USA
| | - Zvi Kelman
- Institute for Bioscience and Biotechnology Research, National Institute of Standards and Technology, University of Maryland, Rockville, MD, USA
- Biomolecular Labeling Laboratory, Institute for Bioscience and Biotechnology Research, Rockville, MD, USA
| | - Sung Hyun Kim
- Department of BioNanoScience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - Bernhard Kuster
- Chair of Proteomics and Bioanalytics, Technische Universität München, Freising, Germany
- Bavarian Center for Biomolecular Mass Spectrometry, Freising, Germany
| | - David Rodriguez-Larrea
- Department of Biochemistry and Molecular Biology, Biofisika Institute (CSIC, UPV/EHU), Leioa, Spain
| | - Stuart Lindsay
- Biodesign Institute, School of Molecular Sciences, Department of Physics, Arizona State University, Tempe, AZ, USA
| | - Giovanni Maglia
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, the Netherlands
| | - Edward M Marcotte
- Department of Molecular Biosciences, Center for Systems and Synthetic Biology, University of Texas at Austin, Austin, TX, USA
| | - John P Marino
- Institute for Bioscience and Biotechnology Research, National Institute of Standards and Technology, University of Maryland, Rockville, MD, USA
| | | | - Michael Mayer
- Adolphe Merkle Institute, University of Fribourg, Fribourg, Switzerland
| | - Patroklos Samaras
- Chair of Proteomics and Bioanalytics, Technische Universität München, Freising, Germany
| | - Kumar Sarthak
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Lusia Sepiashvili
- University of Toronto, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Derek Stein
- Department of Physics, Brown University, Providence, RI, USA
| | - Meni Wanunu
- Department of Physics, Northeastern University, Boston, MA, USA
- Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA, USA
| | - Mathias Wilhelm
- Chair of Proteomics and Bioanalytics, Technische Universität München, Freising, Germany
| | - Peng Yin
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA, USA
- Department of Systems Biology, Harvard Medical School, Boston, MA, USA
| | - Amit Meller
- Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
- Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa, Israel.
| | - Chirlmin Joo
- Department of BioNanoScience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands.
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16
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Zhuang X, Wu Q, Zhang A, Liao L, Fang B. Single-molecule biotechnology for protein researches. Chin J Chem Eng 2021. [DOI: 10.1016/j.cjche.2020.10.031] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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17
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Lindsay S. Ubiquitous Electron Transport in Non-Electron Transfer Proteins. Life (Basel) 2020; 10:life10050072. [PMID: 32443721 PMCID: PMC7281237 DOI: 10.3390/life10050072] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Revised: 05/14/2020] [Accepted: 05/18/2020] [Indexed: 12/15/2022] Open
Abstract
Many proteins that have no known role in electron transfer processes are excellent electronic conductors. This surprising characteristic is not generally evident in bulk aggregates or crystals, or in isolated, solvated peptides, because the outer hydrophilic shell of the protein presents a barrier to charge injection. Ligands that penetrate this barrier make excellent electrical contacts, yielding conductivities on the order of a S/m. The Fermi Energy of metal electrodes is aligned with the energy of internal electronic states of the protein, as evidenced by resonant transmission peaks at about 0.3V on the Normal Hydrogen Electrode scale. This energy is about 0.7 V less than the oxidation potential of aromatic amino acids, indicating a large reduction in electrostatic reorganization energy losses in the interior of the proteins. Consistent with a possible biological role for this conductance, there is a strong dependence on protein conformation. Thus, direct measurement of conductance is a powerful new way to read out protein conformation in real time, opening the way to new types of single molecule sensors and sequencing devices.
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Affiliation(s)
- Stuart Lindsay
- Biodesign Institute, Department of Physics and School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
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18
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Zhang B, Song W, Brown J, Nemanich R, Lindsay S. Electronic Conductance Resonance in Non-Redox-Active Proteins. J Am Chem Soc 2020; 142:6432-6438. [PMID: 32176496 DOI: 10.1021/jacs.0c01805] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
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 ∼0.7 V 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.
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Affiliation(s)
- Bintian Zhang
- Biodesign Institute, Arizona State University, Tempe, Arizona 87287, United States
| | - Weisi Song
- Biodesign Institute, Arizona State University, Tempe, Arizona 87287, United States
| | - Jesse Brown
- Department of Physics, Arizona State University, Tempe, Arizona 87287, United States
| | - Robert Nemanich
- Department of Physics, Arizona State University, Tempe, Arizona 87287, United States
| | - Stuart Lindsay
- Biodesign Institute, Arizona State University, Tempe, Arizona 87287, United States.,Department of Physics, Arizona State University, Tempe, Arizona 87287, United States.,School of Molecular Sciences, Arizona State University, Tempe, Arizona 87287, United States
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