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Towards more reliable AFM force-curve evaluation: A method for spring constant selection, adaptive lever sensitivity calibration and fitting boundary identification. Micron 2019; 125:102717. [PMID: 31376576 DOI: 10.1016/j.micron.2019.102717] [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: 06/05/2019] [Revised: 07/17/2019] [Accepted: 07/17/2019] [Indexed: 11/23/2022]
Abstract
This work discusses key issues regarding the atomic force microscopy (AFM) force-curve evaluation practice, which can affect the determined Young's modulus of the investigated sample. These issues are 1) the proper calibration of lever sensitivity and the effect of its variation between the measurements; 2) the selection of proper cantilever spring constant for the investigated sample; and 3) the selection of the fitting boundaries for the contact mechanics model-based force-curve evaluation. A method is proposed, which solves the above mentioned issues, namely, categorizes the obtained force-curves based on the relation between the elastic properties of the sample and the spring constant of the cantilever, and thus helps in the selection of the proper spring constant for the given surface; helps in the identification of the optimal model-fitting boundaries, and also, provides a way of adaptive lever sensitivity calibration. The method is demonstrated on PDMS (polydimethylsiloxane) samples, which were irradiated with various fluences of ion beams to control their elastic properties in the 4 MPa - 22 GPa range. Our proposed method, if applied correctly can significantly increase the reliability of AFM force-curve evaluation.
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Chen S, Cheng Y, Zhang G, Zhang YW. Spontaneous directional motion of water molecules in single-walled carbon nanotubes with a stiffness gradient. NANOSCALE ADVANCES 2019; 1:1175-1180. [PMID: 36133202 PMCID: PMC9473219 DOI: 10.1039/c8na00322j] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Accepted: 12/19/2018] [Indexed: 06/11/2023]
Abstract
Controlling water molecular motion at the nanoscale is critical for many important applications, such as water splitting to produce hydrogen and oxygen, biological and chemical cell reactions, nanofluidics, drug delivery, water treatment, etc. In this paper, we propose a new nanoscale device based on carbon nanotubes (CNTs) with a stiffness gradient to create a spontaneous directional motion of water molecules, and perform molecular dynamics simulations to analyze its transport characteristics. We find that the (6, 6) CNT possesses an optimal water transport rate. In the thinner CNTs, the water molecules are strongly confined by the CNT wall, resulting in a higher friction force; while in the thicker CNTs, the driving force is lower, and the water molecules tend to form ring-like configurations, resulting in a slower motion. For the (6, 6) CNT, water molecules tend to favor a chain-like configuration, through which the molecules are able to move synergistically along the stiffness gradient, and the transportation efficiency increases with the stiffness gradient but decreases with temperature. Both energetic and kinetic analyses are performed to elucidate this fascinating directional motion. Our work demonstrates a new strategy for controlling water molecular motion at the nanoscale without resorting to any active driving source, such as electric field, temperature or pressure difference.
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Affiliation(s)
- Shuai Chen
- Institute of High Performance Computing, ASTAR 138632 Singapore
| | - Yuan Cheng
- Institute of High Performance Computing, ASTAR 138632 Singapore
| | - Gang Zhang
- Institute of High Performance Computing, ASTAR 138632 Singapore
| | - Yong-Wei Zhang
- Institute of High Performance Computing, ASTAR 138632 Singapore
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Sarker S, Terrón MC, Khandokar Y, Aragão D, Hardy JM, Radjainia M, Jiménez-Zaragoza M, de Pablo PJ, Coulibaly F, Luque D, Raidal SR, Forwood JK. Structural insights into the assembly and regulation of distinct viral capsid complexes. Nat Commun 2016; 7:13014. [PMID: 27698405 PMCID: PMC5059447 DOI: 10.1038/ncomms13014] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 08/25/2016] [Indexed: 01/24/2023] Open
Abstract
The assembly and regulation of viral capsid proteins into highly ordered macromolecular complexes is essential for viral replication. Here, we utilize crystal structures of the capsid protein from the smallest and simplest known viruses capable of autonomously replicating in animal cells, circoviruses, to establish structural and mechanistic insights into capsid morphogenesis and regulation. The beak and feather disease virus, like many circoviruses, encode only two genes: a capsid protein and a replication initiation protein. The capsid protein forms distinct macromolecular assemblies during replication and here we elucidate these structures at high resolution, showing that these complexes reverse the exposure of the N-terminal arginine rich domain responsible for DNA binding and nuclear localization. We show that assembly of these complexes is regulated by single-stranded DNA (ssDNA), and provide a structural basis of capsid assembly around single-stranded DNA, highlighting novel binding interfaces distinct from the highly positively charged N-terminal ARM domain. Circoviruses are the simplest viruses known to autonomously replicate in vertebrates. Here the authors present three structures for distinct macromolecular assemblies of the capsid protein from the beak and feather disease virus that provides insights into the regulation of viral capsid assembly.
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Affiliation(s)
- Subir Sarker
- School of Animal and Veterinary Sciences, Charles Sturt University, Boorooma Street, Wagga Wagga, New South Wales 2678, Australia.,Graham Centre for Agricultural Innovation, NSW Department of Primary Industries and Charles Sturt University, Boorooma Street, Wagga Wagga, New South Wales 2678, Australia
| | - María C Terrón
- Centro Nacional de Microbiología/ISCIII, Majadahonda, Madrid 28220, Spain
| | - Yogesh Khandokar
- School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, New South Wales 2678, Australia
| | - David Aragão
- Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia
| | - Joshua M Hardy
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria 3800, Australia
| | - Mazdak Radjainia
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria 3800, Australia
| | | | - Pedro J de Pablo
- Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain.,Insituto de Física de la Materia Condensada (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Fasséli Coulibaly
- Infection and Immunity Program, Monash Biomedicine Discovery Institute and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria 3800, Australia
| | - Daniel Luque
- Centro Nacional de Microbiología/ISCIII, Majadahonda, Madrid 28220, Spain
| | - Shane R Raidal
- School of Animal and Veterinary Sciences, Charles Sturt University, Boorooma Street, Wagga Wagga, New South Wales 2678, Australia.,Graham Centre for Agricultural Innovation, NSW Department of Primary Industries and Charles Sturt University, Boorooma Street, Wagga Wagga, New South Wales 2678, Australia
| | - Jade K Forwood
- Graham Centre for Agricultural Innovation, NSW Department of Primary Industries and Charles Sturt University, Boorooma Street, Wagga Wagga, New South Wales 2678, Australia.,School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, New South Wales 2678, Australia
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