Reduction of the Damping on an AFM Cantilever in Fluid by the Use of Micropillars

Kawakami, Masaru; Taniguchi, Yukinori; Hiratsuka, Yuichi; Shimoike, Masahiko; Smith, D. A.

doi:10.1021/la902472h

Cited by 8 publications

(8 citation statements)

References 27 publications

(40 reference statements)

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“…This proximity increases a cantilever’s hydrodynamic damping, a phenomenon called squeezed-film damping in AFM and conceptually similar to Faxen’s law in optical-trapping studies . Increased damping near a surface degrades short-term force precision …”

Section: Resultsmentioning

confidence: 95%

“…35 Increased damping near a surface degrades short-term force precision. 36 Characterizing cantilever motion as a function of frequency (f) allows for easy identification of two regimes: thermal-and instrumentation-limited performance. The force power spectral density (PSD) was calculated from a set of five 100 s records for each cantilever (Figure 1d) (Methods).…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Improved Single Molecule Force Spectroscopy Using Micromachined Cantilevers

Bull

Sullan

et al. 2014

ACS Nano

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Enhancing the short-term force precision of atomic force microscopy (AFM) while maintaining excellent long-term force stability would result in improved performance across multiple AFM modalities, including single molecule force spectroscopy (SMFS). SMFS is a powerful method to probe the nanometer-scale dynamics and energetics of biomolecules (DNA, RNA, and proteins). The folding and unfolding rates of such macromolecules are sensitive to sub-pN changes in force. Recently, we demonstrated sub-pN stability over a broad bandwidth (Δf = 0.01-16 Hz) by removing the gold coating from a 100 μm long cantilever. However, this stability came at the cost of increased short-term force noise, decreased temporal response, and poor sensitivity. Here, we avoided these compromises while retaining excellent force stability by modifying a short (L = 40 μm) cantilever with a focused ion beam. Our process led to a ∼10-fold reduction in both a cantilever's stiffness and its hydrodynamic drag near a surface. We also preserved the benefits of a highly reflective cantilever while mitigating gold-coating induced long-term drift. As a result, we extended AFM's sub-pN bandwidth by a factor of ∼50 to span five decades of bandwidth (Δf ≈ 0.01-1000 Hz). Measurements of mechanically stretching individual proteins showed improved force precision coupled with state-of-the-art force stability and no significant loss in temporal resolution compared to the stiffer, unmodified cantilever. Finally, these cantilevers were robust and were reused for SFMS over multiple days. Hence, we expect these responsive, yet stable, cantilevers to broadly benefit diverse AFM-based studies.

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Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

Improved Single Molecule Force Spectroscopy Using Micromachined Cantilevers

Bull

Sullan

et al. 2014

ACS Nano

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“…In multifrequency AFM imaging, higher modes allow the material characteristics, e.g., mechanical, magnetic or electrical properties, of the substrate to be measured [5]. To reduce squeeze-film damping, AFM samples have been placed on pillars [6], or cantilever geometries have been optimized by focused-ion beam milling [7]. In cantilever-based sensor applications, the use of higher vibrational modes provides increased mass sensitivity [8] and allows the elastic properties [9] and the position of adsorbates [10] to be disentangled.…”

Section: Introductionmentioning

confidence: 99%

Influence of squeeze-film damping on higher-mode microcantilever vibrations in liquid

2014

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Background: The functionality of atomic force microscopy (AFM) and nanomechanical sensing can be enhanced using higher-mode microcantilever vibrations. Both methods require a resonating microcantilever to be placed close to a surface, either a sample or the boundary of a microfluidic channel. Below a certain cantilever-surface separation, the confined fluid induces squeeze-film damping. Since damping changes the dynamic properties of the cantilever and decreases its sensitivity, it should be considered and minimized. Although squeeze-film damping in gases is comprehensively described, little experimental data is available in liquids, especially for higher-mode vibrations. Methods: We have measured the flexural higher-mode response of photothermally driven microcantilevers vibrating in water, close to a parallel surface with gaps ranging from~200 μm to~1 μm. A modified model based on harmonic oscillator theory was used to determine the modal eigenfrequencies and quality factors, which can be converted into co-moving fluid mass and dissipation coefficients. Results: The range of squeeze-film damping between the cantilever and surface decreased for eigenfrequencies (inertial forces) and increased for quality factors (dissipative forces) with higher mode number. Conclusions:The results can be employed to improve the quantitative analysis of AFM measurements, design miniaturized sensor fluid cells, or benchmark theoretical models.

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“…To elucidate the microenvironment effect on the mechanism of force-induced unfolding, dynamic force spectroscopy (DFS) was employed to reveal the free-energy landscape. Because of the extremely low viscosity of air and resulting weak hydrodynamic drag on the cantilever beam, the air-phase SMFS method can diminish the squeezing effect (i.e., an increment of the hydrodynamic drag while the AFM tip is close to the surface). ,,, The range affected by the squeezing effect (distance Z ) is significantly smaller in air than that in liquid (Figure S8). The distance Z reaches around 960 nm at a retraction velocity of 100 μm/s in liquid.…”

Section: Resultsmentioning

confidence: 99%

Unfolding of a Single Polymer Chain from the Single Crystal by Air-Phase Single-Molecule Force Spectroscopy: Toward Better Force Precision and More Accurate Description of Molecular Behaviors

et al. 2018

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Understanding the mechanisms of the mechanical deformation of lamellar crystals at the molecular level is of prime importance to rational design of advanced crystalline polymer materials. Single-molecule force spectroscopy (SMFS) can directly characterize molecular behavior and kinetic parameters that are masked in ensemble measurements. However, current SMFS approach cannot sufficiently manipulate a single molecule in air, which is the real working condition for most crystalline polymer materials. Here, we establish an air-phase atomic force microscopy (AFM)-based SMFS method that allows the unfolding of a single helical poly(ethylene oxide) (PEO) chain from the single crystal in air. Our results show that the mechanostability of PEO stem and unfolding potential are significantly enhanced in air compared with the case in liquid. The airphase SMFS method can achieve a much better force precision of 4 pN even at rapid stretching velocity of ∼100 μm/s. Moreover, some intermediate states (e.g., the movement of helical loop within the crystal phase), which were not detectable by using liquid-phase SMFS, have been identified by air-phase SMFS. Therefore, this proposed approach opens new ways for investigating the nanomechanical properties and corresponding molecular mechanism of polymer materials used in solvent-free state.

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Reduction of the Damping on an AFM Cantilever in Fluid by the Use of Micropillars

Cited by 8 publications

References 27 publications

Improved Single Molecule Force Spectroscopy Using Micromachined Cantilevers

Improved Single Molecule Force Spectroscopy Using Micromachined Cantilevers

Influence of squeeze-film damping on higher-mode microcantilever vibrations in liquid

Unfolding of a Single Polymer Chain from the Single Crystal by Air-Phase Single-Molecule Force Spectroscopy: Toward Better Force Precision and More Accurate Description of Molecular Behaviors

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