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Zhou L, Zhu R, Figueroa-Miranda G, Neis M, Offenhäusser A, Mayer D. Ratiometric electrochemical aptasensor with strand displacement for insulin detection in blood samples. Anal Chim Acta 2024; 1317:342823. [PMID: 39029996 DOI: 10.1016/j.aca.2024.342823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2024] [Revised: 05/30/2024] [Accepted: 06/03/2024] [Indexed: 07/21/2024]
Abstract
BACKGROUND Diabetes patients suffer either from insulin deficiency or resistance with a high risk of severe long-term complications, thus the quantitative assessment of insulin level is highly desired for diabetes surveillance and management. Utilizing insulin-capturing aptamers may facilitate the development of affordable biosensors however, their rigid G-quadruplex structures impair conformational changes of the aptamers and diminish the sensor signals. RESULTS Here we report on a ratiometric, electrochemical insulin aptasensor which is achieved by hybridization of an insulin-capturing aptamer and a partially complementary ssDNA to break the rigid G-quadruplex structures. To improve the durability of the aptasensor, the capturing aptamer was immobilized on gold electrodes via two dithiol-phosphoramidite functional groups while methoxy-polyethylene glycol thiol was used as a blocking molecule. The exposure of the sensor to insulin-containing solutions induced the dissociation of the hybridized DNA accompanied by a conformational rearrangement of the capturing aptamer back into a G-quadruplex structure. The reliability of sensor readout was improved by the adoption of an AND logic gate utilizing anthraquinone and methylene blue redox probes associated to the aptamer and complementary strand, respectively. Our aptasensor possessed an improved detection limit of 0.15 nM in comparison to aptasensors without strand displacement. SIGNIFICANCE The sensor was adapted for detection in real blood and is ready for future PoC diagnostics. The capability of monitoring the insulin level in an affordably manner can improve the treatment for an increasing number of patients in developed and developing nations. The utilization of low-cost and versatile aptamer receptors together with the engineering of ratiometric electrochemical signal recording has the potential to considerably advance the current insulin detection technology toward multi-analyte diabetes sensors.
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Affiliation(s)
- Lei Zhou
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich GmbH, Jülich, Germany; Faculty I, RWTH Aachen University, Aachen, Germany
| | - Ruifeng Zhu
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Gabriela Figueroa-Miranda
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Marc Neis
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Andreas Offenhäusser
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Dirk Mayer
- Institute of Biological Information Processing, Bioelectronics (IBI-3), Forschungszentrum Jülich GmbH, Jülich, Germany.
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Taylor AMK, Okoniewski SR, Uyetake L, Perkins TT. Force-Activated DNA Substrates for In Situ Generation of ssDNA and Designed ssDNA/dsDNA Structures in an Optical-Trapping Assay. Methods Mol Biol 2022; 2478:273-312. [PMID: 36063324 DOI: 10.1007/978-1-0716-2229-2_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Single-molecule force spectroscopy can precisely probe the biomechanical interactions of proteins that unwind duplex DNA and bind to and wrap around single-stranded (ss)DNA. Yet assembly of the required substrates, which often contain a ssDNA segment embedded within a larger double-stranded (ds)DNA construct, can be time-consuming and inefficient, particularly when using a standard three-way hybridization protocol. In this chapter, we detail how to construct a variety of force-activated DNA substrates more efficiently. To do so, we engineered a dsDNA molecule with a designed sequence of specified GC content positioned between two enzymatically induced, site-specific nicks. Partially pulling this substrate into the overstretching transition of DNA (~65 pN) using an optical trap led to controlled dissociation of the ssDNA segment delineated by the two nicks. Here, we describe protocols for generating ssDNA of up to 1000 nucleotides as well as more complex structures, such as a 120-base-pair DNA hairpin positioned next to a 33-nucleotide ssDNA segment. The utility of the hairpin substrate was demonstrated by measuring the motion of E. coli. RecQ, a 3'-to-5' DNA helicase.
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Affiliation(s)
- Arnulf M K Taylor
- JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, CO, USA
- Department of Physics, University of Colorado, Boulder, CO, USA
| | - Stephen R Okoniewski
- JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, CO, USA
- Department of Physics, University of Colorado, Boulder, CO, USA
| | - Lyle Uyetake
- JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, CO, USA
| | - Thomas T Perkins
- JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, CO, USA.
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO, USA.
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3
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Parallelized DNA tethered bead measurements to scrutinize DNA mechanical structure. Methods 2019; 169:46-56. [PMID: 31351926 DOI: 10.1016/j.ymeth.2019.07.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 07/01/2019] [Accepted: 07/22/2019] [Indexed: 01/05/2023] Open
Abstract
Tethering beads to DNA offers a panel of single molecule techniques for the refined analysis of the conformational dynamics of DNA and the elucidation of the mechanisms of enzyme activity. Recent developments include the massive parallelization of these techniques achieved by the fabrication of dedicated nanoarrays by soft nanolithography. We focus here on two of these techniques: the Tethered Particle motion and Magnetic Tweezers allowing analysis of the behavior of individual DNA molecules in the absence of force and under the application of a force and/or a torque, respectively. We introduce the experimental protocols for the parallelization and discuss the benefits already gained, and to come, for these single molecule investigations.
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4
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Campuzano S, Yáñez-Sedeño P, Pingarrón JM. Tailoring Sensitivity in Electrochemical Nucleic Acid Hybridization Biosensing: Role of Surface Chemistry and Labeling Strategies. ChemElectroChem 2018. [DOI: 10.1002/celc.201800667] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Susana Campuzano
- Departamento de Química Analítica, Facultad de CC. Químicas; Universidad Complutense de Madrid; E-28040 Madrid Spain
| | - Paloma Yáñez-Sedeño
- Departamento de Química Analítica, Facultad de CC. Químicas; Universidad Complutense de Madrid; E-28040 Madrid Spain
| | - José Manuel Pingarrón
- Departamento de Química Analítica, Facultad de CC. Químicas; Universidad Complutense de Madrid; E-28040 Madrid Spain
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5
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Zhao X, Zeng X, Lu C, Yan J. Studying the mechanical responses of proteins using magnetic tweezers. NANOTECHNOLOGY 2017; 28:414002. [PMID: 28766506 DOI: 10.1088/1361-6528/aa837e] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The mechanical stability of proteins has been extensively studied using AFM as a single-molecule force spectroscopy method. While this has led to many important results, these studies have been mainly limited to fast unfolding at a high-force regime due to the rapid mechanical drift in most AFM stretching experiments. Therefore, there is a gap between the knowledge obtained at a high-force regime and the mechanical properties of proteins at a lower force regime which is often more physiologically relevant. Recent studies have demonstrated that this gap can be addressed by stretching single protein molecules using magnetic tweezers, due to the excellent mechanical stability this technology offers. Here we review magnetic tweezers technology and its current application in studies of the force-dependent stability and interactions of proteins.
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Affiliation(s)
- Xiaodan Zhao
- Mechanobiology Institute, National University of Singapore, 5A Engineering Drive 1, 117411, Singapore
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6
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Xu H, Jones S, Choi BC, Gordon R. Characterization of Individual Magnetic Nanoparticles in Solution by Double Nanohole Optical Tweezers. NANO LETTERS 2016; 16:2639-43. [PMID: 26977716 DOI: 10.1021/acs.nanolett.6b00288] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
We study individual superparamagnetic Fe3O4 (magnetite) nanoparticles in solution using a double nanohole optical tweezer with magnetic force setup. By analysis of the trapping optical transmission signal (step size, autocorrelation, the root-mean-square signal, and the distribution with applied magnetic field), we are able to measure the refractive index, magnetic susceptibility, remanence and size of each trapped nanoparticle. The size distribution is found to agree well with scanning electron microscopy measurements, and the permeability, magnetic susceptibility and remanence values are all in agreement with published results. Our approach demonstrates the versatility of the optical tweezer with magnetic field setup to characterize nanoparticles in fluidic mixtures with potential for isolation of desired particles and pick-and-place functionality.
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Affiliation(s)
- Haitian Xu
- Department of Physics and Astronomy and ‡Department of Electrical and Computer Engineering, University of Victoria , Victoria V8P 5C2, Canada
| | - Steven Jones
- Department of Physics and Astronomy and ‡Department of Electrical and Computer Engineering, University of Victoria , Victoria V8P 5C2, Canada
| | - Byoung-Chul Choi
- Department of Physics and Astronomy and ‡Department of Electrical and Computer Engineering, University of Victoria , Victoria V8P 5C2, Canada
| | - Reuven Gordon
- Department of Physics and Astronomy and ‡Department of Electrical and Computer Engineering, University of Victoria , Victoria V8P 5C2, Canada
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7
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Li Z, Zhang S, Tong L, Wang P, Dong B, Xu H. Ultrasensitive size-selection of plasmonic nanoparticles by Fano interference optical force. ACS NANO 2014; 8:701-708. [PMID: 24308824 DOI: 10.1021/nn405364u] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In this paper, we propose a solution for the ultrasensitive optical selection of plasmonic nanoparticles using Fano interference-induced scattering forces. Under a Gaussian beam excitation, the scattering of a plasmonic nanoparticle at its Fano resonance becomes strongly asymmetric in the lateral direction and consequently results in a net transverse scattering force, that is, Fano interference-induced force. The magnitude of this transverse scattering force is comparable with the gradient force in conventional optical manipulation experiments. More interestingly, the Fano scattering force is ultrasensitive to the particle size and excitation frequency due to the phase sensitivity of the interference between adjacent plasmon modes in the particle. Utilizing this distinct feature, we show the possibility of size-selective sorting of silver and gold nanoparticles with an accuracy of about ±10 nm and silica-gold core-shell nanoparticles with shell thickness down to several nanometers. These results would add to the toolbox of optical manipulation and fabrication.
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Affiliation(s)
- Zhipeng Li
- Beijing Key Laboratory of Nano-Photonics and Nano-Structure (NPNS), Department of Physics, Capital Normal University , Beijing 100048, PR China
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8
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Mack AH, Schlingman DJ, Regan L, Mochrie SGJ. Practical axial optical trapping. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:103106. [PMID: 23126750 PMCID: PMC3482253 DOI: 10.1063/1.4757862] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Accepted: 09/19/2012] [Indexed: 06/01/2023]
Abstract
We describe a new method for calibrating optical trapping measurements in which tension is applied in the direction of the laser beam to a molecule tethered between a surface and an optically trapped bead. Specifically, we present a generally-applicable procedure for converting from the measured scattering intensity and the measured stage displacement to applied tension and bead-coverslip separation, using measurements of the light intensity scattered from an untethered, trapped bead. Our calibration accounts for a number of effects, including aberrations and the interference of forward-reflected bead-scattered light with the trapping beam. To demonstrate the accuracy of our method, we show measurements of the DNA force-versus-extension relation using a range of laser intensities, and show that these measurements match the expected extensible wormlike-chain (WLC) behavior. Finally, we also demonstrate a force-clamp, in which the tension in a tether is held fixed while the extension varies as a result of molecular events.
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Affiliation(s)
- A H Mack
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut 06511, USA
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9
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Greatly extended storage stability of electrochemical DNA biosensors using ternary thiolated self-assembled monolayers. Talanta 2012; 99:155-60. [DOI: 10.1016/j.talanta.2012.05.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2012] [Revised: 05/17/2012] [Accepted: 05/18/2012] [Indexed: 11/23/2022]
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10
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Plénat T, Tardin C, Rousseau P, Salomé L. High-throughput single-molecule analysis of DNA-protein interactions by tethered particle motion. Nucleic Acids Res 2012; 40:e89. [PMID: 22422843 PMCID: PMC3384352 DOI: 10.1093/nar/gks250] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 02/21/2012] [Accepted: 03/05/2012] [Indexed: 11/19/2022] Open
Abstract
Tethered particle motion (TPM) monitors the variations in the effective length of a single DNA molecule by tracking the Brownian motion of a bead tethered to a support by the DNA molecule. Providing information about DNA conformations in real time, this technique enables a refined characterization of DNA-protein interactions. To increase the output of this powerful but time-consuming single-molecule assay, we have developed a biochip for the simultaneous acquisition of data from more than 500 single DNA molecules. The controlled positioning of individual DNA molecules is achieved by self-assembly on nanoscale arrays fabricated through a standard microcontact printing method. We demonstrate the capacity of our biochip to study biological processes by applying our method to explore the enzymatic activity of the T7 bacteriophage exonuclease. Our single molecule observations shed new light on its behaviour that had only been examined in bulk assays previously and, more specifically, on its processivity.
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Affiliation(s)
- Thomas Plénat
- Centre National de la Recherche Scientifique, Institut de Pharmacologie et de Biologie Structurale, 205 route de Narbonne, Toulouse, F-31077, Université de Toulouse, UPS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, F-31077, Université de Toulouse, UPS, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000 and Centre National de la Recherche Scientifique, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000, France
| | - Catherine Tardin
- Centre National de la Recherche Scientifique, Institut de Pharmacologie et de Biologie Structurale, 205 route de Narbonne, Toulouse, F-31077, Université de Toulouse, UPS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, F-31077, Université de Toulouse, UPS, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000 and Centre National de la Recherche Scientifique, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000, France
| | - Philippe Rousseau
- Centre National de la Recherche Scientifique, Institut de Pharmacologie et de Biologie Structurale, 205 route de Narbonne, Toulouse, F-31077, Université de Toulouse, UPS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, F-31077, Université de Toulouse, UPS, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000 and Centre National de la Recherche Scientifique, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000, France
| | - Laurence Salomé
- Centre National de la Recherche Scientifique, Institut de Pharmacologie et de Biologie Structurale, 205 route de Narbonne, Toulouse, F-31077, Université de Toulouse, UPS, Institut de Pharmacologie et de Biologie Structurale, Toulouse, F-31077, Université de Toulouse, UPS, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000 and Centre National de la Recherche Scientifique, Laboratoire de Microbiologie et Génétique Moléculaires, Toulouse, F-31000, France
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11
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Mie Y, Kojima N, Kowata K, Komatsu Y. End-tether Structure of DNA Alters Electron-transfer Pathway of Redox-labeled Oligo-DNA Duplex at Electrode Surface. CHEM LETT 2012. [DOI: 10.1246/cl.2012.62] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Yasuhiro Mie
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)
| | - Naoshi Kojima
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)
| | - Keiko Kowata
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)
| | - Yasuo Komatsu
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)
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12
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Paik DH, Perkins TT. Single-molecule optical-trapping measurements with DNA anchored to an array of gold nanoposts. Methods Mol Biol 2012; 875:335-356. [PMID: 22573450 DOI: 10.1007/978-1-61779-806-1_18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Gold-thiol chemistry is one of the most successful chemistries for conjugating biomolecules to surfaces, but such chemistry has not been exploited in optical-trapping experiments because of laser-induced ablation of gold. In this work, we describe a method to combine these two separate technologies without undue heating using DNA anchored to gold nanostructures (r = 50-250 nm; h ≈ 20 nm). Moreover, we demonstrate a quantitative and mechanically robust (>100 pN) optical-trapping assay. By using three dithiol phosphoramidites (DTPAs) incorporated into a polymerase chain reaction (PCR) primer, the gold-DNA bond remained stable in the presence of excess thiolated compounds. This chemical robustness allowed us to reduce nonspecific sticking by passivating the unreacted gold with methoxy-(polyethylene glycol)-thiol (mPEG-SH). Overall, this surface conjugation of biomolecules onto an ordered array of gold nanostructures by chemically and mechanically robust bonds provides a unique way to carry out spatially controlled, repeatable measurements of single molecules.
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Affiliation(s)
- D Hern Paik
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO, USA
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13
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Campuzano S, Kuralay F, Wang J. Ternary Monolayer Interfaces for Ultrasensitive and Direct Bioelectronic Detection of Nucleic Acids in Complex Matrices. ELECTROANAL 2011. [DOI: 10.1002/elan.201100452] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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14
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Day BS, Fiegland LR, Vint ES, Shen W, Morris JR, Norton ML. Thiolated dendrimers as multi-point binding headgroups for DNA immobilization on gold. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:12434-12442. [PMID: 21916426 DOI: 10.1021/la202444s] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The synthesis of multithiolated DNA molecules that can be used to produce self-assembled monolayers of single-stranded DNA oligonucleotides on gold substrates is described. Generation 3 polyamidoamine (PAMAM) dendrimers were conjugated to DNA oligomers and functionalized with ~30 protected thiol groups. The protected thiol groups-thioacetate groups-allowed the dendrimer-DNA constructs to be stored in a buffer solution for at least 2 months before deprotection without any observable decrease in their ability to assemble into functional layers. The monolayers formed using these multithiolated DNA probe strands demonstrate target capture efficiencies comparable to those of analogous monolayers assembled with DNA functionalized with single thiol groups. A functional advantage of using dendrimer headgroups is the resistance to probe strand loss in prolonged exposure to buffer solutions at a high temperature (95 °C).
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Affiliation(s)
- B Scott Day
- Department of Chemistry, Marshall University, Huntington, West Virginia 25755, USA.
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15
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Paik DH, Perkins TT. Overstretching DNA at 65 pN does not require peeling from free ends or nicks. J Am Chem Soc 2011; 133:3219-21. [PMID: 21207940 DOI: 10.1021/ja108952v] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
DNA exhibits a remarkable mechanical transition where its extension increases by 70% at 65 pN. Notwithstanding more than a decade of experimental and theoretical studies, there remains a significant debate on the nature of overstretched DNA. We developed a topologically closed but rotationally unconstrained DNA assay, which contains no nicks or free ends. DNA in this assay exhibited the canonical overstretching transition at 65 pN but without hysteresis upon retraction (v(stage) = 5 μm/s). Introduction of a controlled nick led to hysteresis in the force-extension curve. Moreover, the degree of hysteresis increased with the number of nicks. Hence, the generation of single-stranded DNA from free ends or nicks is not an obligatory step in overstretching DNA, but rather a consequence.
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Affiliation(s)
- D Hern Paik
- JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, Colorado 80309, USA
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Schlingman DJ, Mack AH, Mochrie SGJ, Regan L. A new method for the covalent attachment of DNA to a surface for single-molecule studies. Colloids Surf B Biointerfaces 2010; 83:91-5. [PMID: 21130613 DOI: 10.1016/j.colsurfb.2010.11.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 09/27/2010] [Accepted: 11/01/2010] [Indexed: 11/19/2022]
Abstract
Attachments between DNA and a surface or bead are often necessary for single-molecule studies of DNA and DNA-protein interactions. In single-molecule mechanical studies using optical or magnetic tweezers, such attachments must be able to withstand the applied forces. Here we present a new method for covalently attaching DNA to a glass surface, which uses N-hydroxysuccinimide (NHS) modified PEG that is suitable for high-force single-molecule mechanical studies. A glass surface is coated with silane-PEG-NHS and DNA is covalently linked through a reaction between the NHS group and an amine modified nucleotide that has been incorporated into the DNA. After DNA attachment, non-reacted NHS groups are hydrolyzed leaving a PEG-covered surface which has the added benefit of reducing non-specific surface interactions. This method permits specific binding of the DNA to the surface through a covalent bond. At the DNA end not attached to the surface, we attach a streptavidin-coated polystyrene bead and measure force-versus-extension using an optical trap. We show that our method allows a tethered DNA molecule to be pulled through its overstretching transition (> 60pN) multiple times. We anticipate this simple yet powerful method will be useful for many researchers.
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Affiliation(s)
- Daniel J Schlingman
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
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