Small‐Amplitude Atomic Force Microscopy

Patil, Shivprasad; Hoffmann, Peter M.

doi:10.1002/adem.200500054

Cited by 19 publications

(15 citation statements)

References 44 publications

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“…Second, any quantitative interpretation of the data requires a model of the tip dynamics. Since both regimes rely on very different interactions between the tip, the interfacial liquid and the solid, no single model is currently applicable at all operating amplitudes, and different theories are required to describe 022407-1 1539-3755/2013/88(2)/022407 (6) ©2013 American Physical Society SA-AFM [14,22,23] and MF-AFM [16,17] results. Finally, an appropriate choice of amplitude may simultaneously provide information about both the solid and the liquid at the interface while retaining molecular-or atomic-level resolution, further emphasizing the need to correctly understand the transition region.…”

Section: Introductionmentioning

confidence: 99%

Anharmonicity, solvation forces, and resolution in atomic force microscopy at the solid-liquid interface

Voïtchovsky

2013

Phys. Rev. E

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Solid-liquid interfaces are central to nanoscale science and technology and control processes as diverse as self-assembly, heterogeneous catalysis, wetting, electrochemistry, or protein function. Experimentally, measuring the structure and dynamics of solid-liquid interfaces with molecular resolution remains a challenge. This task can, in principle, be achieved with atomic force microscopy (AFM), which functions locally, and with nanometer precision. When operated dynamically and at small amplitudes, AFM can provide molecular-level images of the liquid solvation layers at the interfaces. At larger amplitudes, results in the field of multifrequency AFM have shown that anharmonicities in the tip motion can provide quantitative information about the solid's mechanical properties. The two approaches probe opposite aspects of the interface and are generally seen as distinct. Here it is shown that, for amplitudes A < d, the thickness of the solvation region, the tip mainly probes the interfacial liquid, and subnanometer resolution can be achieved through solvation forces. For A > d, the tip trajectory becomes rapidly anharmonic due to the tip tapping the solid, and the resolution decreases. A nonlinear transition between the two regimes occurs for A ∼ d and can be quantified with the second harmonic of the tip oscillation. These results, confirmed by computer simulations, remain valid in most experimental conditions. Significantly, they provide an objective criterion to enhance resolution and to decide whether the results are dominated by the properties of the solid or of the liquid.

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Section: Introductionmentioning

confidence: 99%

Anharmonicity, solvation forces, and resolution in atomic force microscopy at the solid-liquid interface

Voïtchovsky

2013

Phys. Rev. E

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“…While Benedetti et al are correct in pointing out a gross oversimplification of cantilever dynamics in liquid environment, their conclusion, that the internal friction is below detection limit of AFM, is based on experiments carried out with unsuitable parameters (See supplementary information). Indeed, the approach of small amplitudes (∼ 1Å), large cantilever stiffness (∼ 1 N/m) and purely off-resonance operation is essential for dissipation measurement using small amplitude AFM [35]. This has also been the case for probing the dissipation in layering of liquid molecules next to a solid wall using small amplitude AFM [41,47].…”

Section: Discussionmentioning

confidence: 99%

Direct Measurement of Dissipation in a Single Protein using Small Amplitude Atomic Force Microscopy

Rajput

Talele

Ahlawat

et al. 2018

Preprint

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In Krammer's theory, stiffness and dissipation coefficient of a protein determine the rate of their conformational change. Using atomic force microscope, it is possible to measure viscoelasticity of a single protein, wherein it's dissipative and elastic nature is directly and independently measured. Such measurements are performed, either by measuring the thermal fluctuations of the protein held under a constant force, or by providing small modulations to the protein by dithering the cantilever and measuring its response. In small amplitude approximation, where dither amplitude is comparable to persistence length of polymers, it is possible to measure the protein's viscoelastic response accurately. We measured dissipation in I27 at extremely low pulling speeds (∼ 50 nm/s) and low dither frequencies (∼ 100 Hz). At these experimental parameters the dissipation is found to be ∼ 10 −5 kg/s, well above the detection limit of conventional AFM and upper limit predicted by Benedetti et al. Our stiffness data clearly reveals unfolding intermediate of titin's individual immunoglobulin units. The intermediate is elongation of folded domains by ∼ 8Å, wherein two hydrogen bonds are broken between beta sheets. It was possible to measure this elongation in our experiments. The directly measured internal friction of unfolded polymer chain shows a scaling with tension on the chain. The measurements show that it is possible to measure internal friction in single molecules unambiguously using small amplitude AFM. It suggests that systematic experiments to unravel the relation between directly measured internal friction and folding rates of proteins are possible. INTRODUCTIONIn last few decades, a number of experimental techniques have been developed to observe and manipulate matter at atomistic and molecular scales [1][2][3][4][5][6][7][8][9][10]. These developments have a lasting impact on the field of molecular biology as well as on molecular nanotechnology. Single macromolecules such as proteins, flexible polymers and polysaccharides are stretched and coil-to-stretched or folded-to-unfolded transitions under the application of external force are routinely observed. The central goal of these experiments is to mimic the molecular response under natural situations such as ligand-receptor binding, allosteric signalling and the stress induced conformational changes. They measure kinetics of unfolding of a protein and binding affinities of ligands to receptors.Along with optical tweezers [3, 9-12], Atomic Force Microscopy has acquired a unique position in this quest due to its unprecedented spatial resolution in physiological conditions [5][6][7][13][14][15][16][17]. In typical AFM experiment, mica or Au substrate is sparsely coated with the biological macromolecule and is placed in the liquid environment. A sharp probe attached to a cantilever spring is then brought close to a molecule. The protein is allowed to attach to it from either C or N terminus through nonspecific binding. The bending in the cantilever beam is measur...

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“…If the oscillation amplitude is too large, the vibrating tip will traverse long-range, non-linear force fields 52 that preclude the stability of cantilever motion, and inevitably hit the sample regardless of the imaging conditions 29 , resulting in deterioration of the resolution. Aside from the loss in resolution, higher harmonics start to appear in the tip motion and the system becomes more complicated to model 55 .…”

Section: Discussionmentioning

confidence: 99%

“…For example, in water it is easier to achieve molecular-level resolution on hydrophilic mica than on hydrophobic graphite 42,51 . Finally, the spring constant of the cantilever supporting the tip must be selected appropriately 52,53 . When working in these conditions, the AFM does not only provide molecular-level images of the interface, but it also derives information about the local sample-liquid affinity which can be used to gain chemical information about the sample's surface 54 .…”

Section: Introductionmentioning

confidence: 99%

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

Miller

Trewby

Payam

et al. 2016

JoVE

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Atomic force microscopy (AFM) has become a well-established technique for nanoscale imaging of samples in air and in liquid. Recent studies have shown that when operated in amplitude-modulation (tapping) mode, atomic or molecular-level resolution images can be achieved over a wide range of soft and hard samples in liquid. In these situations, small oscillation amplitudes (SAM-AFM) enhance the resolution by exploiting the solvated liquid at the surface of the sample. Although the technique has been successfully applied across fields as diverse as materials science, biology and biophysics and surface chemistry, obtaining high-resolution images in liquid can still remain challenging for novice users. This is partly due to the large number of variables to control and optimize such as the choice of cantilever, the sample preparation, and the correct manipulation of the imaging parameters. Here, we present a protocol for achieving high-resolution images of hard and soft samples in fluid using SAM-AFM on a commercial instrument. Our goal is to provide a step-by-step practical guide to achieving high-resolution images, including the cleaning and preparation of the apparatus and the sample, the choice of cantilever and optimization of the imaging parameters. For each step, we explain the scientific rationale behind our choices to facilitate the adaptation of the methodology to every user's specific system.

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Small‐Amplitude Atomic Force Microscopy

Cited by 19 publications

References 44 publications

Anharmonicity, solvation forces, and resolution in atomic force microscopy at the solid-liquid interface

Anharmonicity, solvation forces, and resolution in atomic force microscopy at the solid-liquid interface

Direct Measurement of Dissipation in a Single Protein using Small Amplitude Atomic Force Microscopy

Sub-nanometer Resolution Imaging with Amplitude-modulation Atomic Force Microscopy in Liquid

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