Amplitude Of Cantilever Research Articles

Fiber-integrated cantilever-based nanomechanical biosensors as a tool for rapid antibiotic susceptibility testing.

There is an urgent need for developing rapid and affordable antibiotic susceptibility testing (AST) technologies to inhibit the overuse of antibiotics. In this study, a novel microcantilever nanomechanical biosensor based on Fabry-Pérot interference demodulation was developed for AST. To construct the biosensor, a cantilever was integrated with the single mode fiber in order to form the Fabry-Pérot interferometer (FPI). After the attachment of bacteria on the cantilever, the fluctuations of cantilever caused by the bacterial movements were detected by monitoring the changes of resonance wavelength in the interference spectrum. We applied this methodology to Escherichia coli and Staphylococcus aureus, showing the amplitude of cantilever's fluctuations was positively related on the quantity of bacteria immobilized on the cantilever and associated with the bacterial metabolism. The response of bacteria to antibiotics was dependent on the types of bacteria, the types and concentrations of antibiotics. Moreover, the minimum inhibitory and bactericidal concentrations for Escherichia coli were obtained within 30 minutes, demonstrating the capacity of this method for rapid AST. Benefiting from the simplicity and portability of the optical fiber FPI-based nanomotion detection device, the developed nanomechanical biosensor in this study provides a promising technique for AST and a more rapid alternative for clinical laboratories.

Standoff Detection of Plastics

Rapid identification of different plastics for recycling is very important in overcoming the plastic waste challenge our society is facing today. An ideal plastic detector should be able to discern different plastics at the molecular level in a standoff fashion where the detector does not come in contact with the target plastic. We have demonstrated a standoff technique for the rapid identification of plastics based on their mid-IR absorption spectra. Since mid-IR region is free of overtones, this region is known as molecular finger print regime This technique is based on a variation of photoacoustic spectroscopy (PAS), where the light from a tunable infrared source, a quantum cascade laser (QCL), is scattered/reflected off the target plastic object. The returning scattered light is collected and made to create acoustic waves on a microfabricated cantilever sensor. Our experimental results show that the cantilever response, resonance frequency, amplitude, and bending, changes with infrared absorption characteristics of the target. A plot of cantilever response as a function of illuminating wavelength mimic the infrared absorption peaks of the plastics material producing a mechanical spectrum. The generated spectrum obtained for different plastics is then compared with that conventional spectrum for polymer identification.

Comparison of atomic force microscopy force curve and solvation structure studied by integral equation theory.

Atomic force microscopy can observe structures of liquids (solvents) on solid surfaces as oscillating force curves. The oscillation originates from the solvation force, which is affected by the interaction between the probe, substrate, and solvents. To investigate the effects of the interactions on the force curve, we calculated the force curves by integral equation theory with various probe and substrate conditions. The probe solvophilicity affected the force curves more than the substrate solvophilicity in our calculation, and its reason is qualitatively explained by the amount of the desolvated solvents. We evaluated the probes and parameters in terms of the qualitative estimation of the number density distribution of the solvent on the wall. The negative of the force curve's derivative with respect to the surface separation reflected the number density distribution better than the force curve. This parameter is based on the method that is proposed previously by Amano et al. [Phys. Chem. Chem. Phys. 18, 15534 (2016)]. The normalized frequency shift can also be used for the qualitative estimation of the number density distribution if the cantilever amplitude is small. Solvophobic probes reflected the number density distribution better than the solvophilic probes. Solvophilic probes resulted in larger oscillation amplitudes than solvophobic probes and are suitable for measurements with a high S/N ratio.

Stochastic resonance induced performance enhancement of MEMS cantilever biosensors

This paper presents an application of stochastic resonance for improving the performance of micro-electromechanical system (MEMS) cantilever biosensors operating in liquid media. The hydrodynamic influences in liquid media that consist of added mass effect, viscous damping and squeeze film damping deteriorate the Q-factor of cantilever oscillator sensors so much that their operation under fluid-immersed conditions becomes impractical. The stochastic resonance can be produced by the addition of noise in two ways: one, by direct transfer of noise energy through some nonlinear interaction process with the oscillator; and second, by making intrinsic parameters of the oscillator noisy. In this work, we are concerned with the second approach where MEMS controlled feedback oscillator is the biosensor. The cantilever motion is modeled as a damped harmonic oscillator with its natural frequency and damping coefficient parameters made noisy for generating stochastic resonance. Both the frequency and the damping noises generate stochastic resonance in the oscillator amplitude; however, the damping noise generates an additional resonance effect in the oscillator phase. The latter creates the possibility for improving Q-factor against the detrimental influences of hydrodynamic loading. This is a novel feature, which we explore in this paper for maintaining self-sustained cantilever oscillations in a liquid medium and for enhancing biosensor performance. The biosensor model takes into account the circuit loading effect and the influence of cantilever noise in hydrodynamic environment as well. The analytical relations for mass sensitivity and limit of detection have been obtained. The limit of detection is found to be inversely proportional to where and denote cantilever amplitude and Q-factor, respectively. That means the phase stochastic resonance produced by the addition of damping noise lowers the limit of detection by enhancing both and . A prototype theoretical analysis with a Si-MEMS cantilever ( μm3 dimensions and 10 μm gap from boundary wall) oscillator sensor in aqueous medium shows 2 to 3 orders of magnitude enhancement in the Q-factor and 4 to 5 orders of magnitude improvement in the limit of mass detection.

A Detection Error Correction Scheme Aiming at Gradient Nonlinear Problem in Cantilever-Based Sensors

Gradient nonlinear problem is generated when cantilever based sensors are applied to the gradient field. The larger the amplitude of cantilever is (that is, the larger the positional change of the free end of cantilever in the gradient field is), the more serious gradient nonlinear problem is. As for a piezoelectric cantilever based current sensor, a higher sensitivity can be obtained by a greater amplitude which intensifies the gradient nonlinear problem that may decrease the detection accuracy. In this study, a detection error correction scheme aiming at gradient nonlinear problem is proposed for the first time. The distance between appliance and cantilever can be regarded as a variable with the scheme. The nonlinear error can be decreased to lower than 10% in the detection range from 2A to 7A based on a piezoelectric cantilever current sensor in the experiment results. Furthermore, the scheme is not only applicable to the gradient magnetic field, but also has implications for the nonlinear problems of other gradient fields and vibration structures.

Universal aspects of sonolubrication in amorphous and crystalline materials

We studied sonolubricity, a phenomenon reducing the friction between two sliding surfaces by ultrasound. Friction force measurements were performed using an atomic force microscope (AFM) when the tip-surface contact was excited to out-of-plane oscillations by a transducer attached to the rear of the sample or by oscillating the AFM cantilever by the built-in piezoelectric element in the cantilever holder. Experiments were carried out near or at the first cantilever contact-resonance. We studied friction on crystalline and amorphous Pd77.5Cu6Si16.5 ribbons, on a silicon wafer at room temperature, and on a La0.6Sr0.4MnO3 (LSMO) thin film at different temperatures. Measurements were carried out varying the cantilever amplitude, the ultrasonic frequency, and the normal static load. The effect of sonolubrication is explained by the non-linear force-distance curve between the sample and the tip due to the local interaction potential. The reduction of friction in LSMO as a function temperature is due to the direct coupling of the tip's stress-field to the electrons.

Dynamic AFM force spectroscopy of DNA using FM mode with constant excitation

We report single-molecule force spectroscopy experiments on double-stranded DNA using a dynamically oscillating AFM cantilever driven in a frequency modulation mode with a constant excitation (CE) amplitude. While the DNA molecule is stretched, we measured the shift of the cantilever amplitude and the resonance frequency and estimated both the conservative forces and the dissipated energy. Typical elastic features of the calculated force distance curves are in nice agreement with data known from quasi-static stretching experiments. Analysis of the data indicates that the melting dynamics of the DNA base pairs depends on the amount of already melted base pairs and the base pair recombination rate. Furthermore, we observe a reduction of the molecular elasticity modulus, which is most likely caused by the cantilever dynamics leading to a destabilization of stacking and hydrogen bond interactions.

In-situ piezoresponse force microscopy cantilever mode shape profiling

The frequency-dependent amplitude and phase in piezoresponse force microscopy (PFM) measurements are shown to be a consequence of the Euler-Bernoulli (EB) dynamics of atomic force microscope (AFM) cantilever beams used to make the measurements. Changes in the cantilever mode shape as a function of changes in the boundary conditions determine the sensitivity of cantilevers to forces between the tip and the sample. Conventional PFM and AFM measurements are made with the motion of the cantilever measured at one optical beam detector (OBD) spot location. A single OBD spot location provides a limited picture of the total cantilever motion, and in fact, experimentally observed cantilever amplitude and phase are shown to be strongly dependent on the OBD spot position for many measurements. In this work, the commonly observed frequency dependence of PFM response is explained through experimental measurements and analytic theoretical EB modeling of the PFM response as a function of both frequency and OBD spot location on a periodically poled lithium niobate sample. One notable conclusion is that a common choice of OBD spot location—at or near the tip of the cantilever—is particularly vulnerable to frequency dependent amplitude and phase variations stemming from dynamics of the cantilever sensor rather than from the piezoresponse of the sample.

Power Variation with Electret Surface Potential and Frequency of Vibration in Vertical Vibration based Cantilever-Electret Micro-Power Generation

A cantilever-electret based electrostatic micro-power generator for energy harvesting was set up in which Cyclic Transparent Optical Polymer (CYTOP) was used as the electret, and the upper electrode was made in form of an Ashaped cantilever which was fabricated from materials of copper with embedded glass epoxy. The cantilever was vibrated in the vertical direction in close to contact point mode of operation. Experimental result showed that the average output power increases with increasing electret surface potential, and the minimum distance to contact point decreases with increasing electret surface potential. Also, variation of output power with frequency was investigated by first observing the natural vibration of the cantilever amplitude with frequency. The natural amplitude was found to decrease with increasing frequency, thus making the average output power to decrease with increasing frequency. However, for the fabricated cantilever when operated over a wide frequency range, it was further confirmed by experiments that the output power variation peaks around 40Hz with maximum output power of 2.7nW with 1MΩ externally connected load and then decreases with increasing frequency. Keywords— Electret, Cantilever, Micro-Power Generator, Energy Harvesting, Average Output Power, Frequency,

Magnetic Resonance Force Microscopy Detected Long-Lived Spin Magnetization.

Magnetic resonance force microscopy (MRFM), which combines magnetic resonance imaging with scanning probe microscopy together, is capable of performing ultra-sensitive detection of spin magnetization. In an attempt to observe dynamic nuclear polarization (DNP) in an MRFM experiment, which could possibly further improve its sensitivity towards a single proton spin, a film of perdeuterated polystyrene doped with a nitroxide electron-spin probe was prepared. A high-compliance cantilever with a 4 μm diameter magnetic tip was brought near the film at a temperature of 7.3 K and in a background magnetic field of ~0.6 T. The film was irradiated with 16.7 GHz microwaves while the resulting transient change in cantilever frequency was recorded in real time. In addition to observing the expected prompt change in cantilever frequency due to saturation of the nitroxide's electron-spin magnetization, we observed a persistent cantilever frequency change. Based on its magnitude, lifetime, and field dependence, we tentatively attribute the persistent signal to polarized deuteron magnetization created via transfer of magnetization from electron spins. Further measurements of the persistent signal's dependence on the cantilever amplitude and tip-sample separation are presented and explained by the cross-effect DNP mechanism in high magnetic field gradients.

Unified picture of cantilever frequency shift measurements of magnetic resonance

We report a unified framework describing all existing protocols for spin manipulation and signal creation in frequency-modulation magnetic resonance force microscopy using classical perturbation theory. The framework is well suited for studying the dependence of the frequency shift on the cantilever amplitude via numerical simulation. We demonstrate the formalism by recovering an exact result for a single spin signal and by simulating, for the first time as a function of cantilever amplitude, the frequency shift due to a volume of noninteracting spins inverted by an adiabatic rapid passage. We show that an optimal cantilever amplitude exists that maximizes the signal. Our findings suggest that understanding the amplitude dependence of the spin signal will be important for designing future high-sensitivity experiments.

Loss tangent imaging: Theory and simulations of repulsive-mode tapping atomic force microscopy

An expression for loss tangent measurement of a surface in amplitude modulation atomic force microscopy is derived using only the cantilever phase and the normalized cantilever amplitude. This provides a direct measurement of substrate compositional information that only requires tuning of the cantilever resonance to provide quantitative information. Furthermore, the loss tangent expression incorporates both the lost and stored energy into one term that represents a fundamental interpretation of the phase signal in amplitude modulation imaging. Numerical solutions of a cantilever tip interacting with a simple Voigt modeled surface agree with the derived loss tangent to within a few percent.

An adaptive feedback circuit for MEMS resonators

The first adaptive feedback circuit capable of detecting resonant frequencies for a wide range of MEMS resonators is presented. The feedback system presented implements a hill-climbing algorithm that sweeps actuation frequencies, locking onto the resonance condition at maximum cantilever amplitude response without limitations on the frequency range. To demonstrate its adaptability, a circuit implementation of this feedback algorithm was used to detect the resonant frequency of eight different cantilever-based sensors (width (W) = 1.4 µm, length (L) = 40–75 µm, and thickness (T) = 1.8 µm), resonating at 201.0 to 592.1 kHz. Additionally, the same circuit was used to track resonant frequency shifts due to isopropanol adsorption on three different chemical sensors with no modifications. The feedback electronics integrated with these resonator sensors provide a mass resolution limit of 123 femptograms. The realization of this system will enable real-time chip-scale sensor systems, providing an alternative to external instrumentation modules that perform sensor control and monitoring.

Mechanical stiffening, bistability, and bit operations in a microcantilever

We investigate the nonlinear dynamics of microcantilevers. We demonstrate mechanical stiffening of the frequency response at large amplitudes, originating from the geometric nonlinearity. At strong driving the cantilever amplitude is bistable. We map the bistable regime as a function of drive frequency and amplitude, and suggest several applications for the bistable microcantilever, of which a mechanical memory is demonstrated.

Nanogold Aggravating MEMS Cantilever Piezoelectric Optical Detection Biochip

A kind of array micro-electromechanical systems (MEMS) cantilever of biochip is designed, which piezoelectric devices drive MEMS cantilever resonance. Before and after hybridization reaction, by the change of the resonant frequency of the cantilever, it can detect the cantilever amplitude through optical detector to judge whether the solution containing the cantilever probe genes. In order to improve detection sensitivity, it aggravate cantilever by gold nanoparticles combining hybridization information, applying Au-S chemical bond of gold nanoparticles and dithiol HS(CH2)6SH to combine and fix DNA probe and applying target DNA marked with biotin to combine gold nanoparticles by Biotin - Streptavidin combining. The results shows that this biochip can detect biological samples fast, high throughput, low cost, high sensitivity and reliably.

Quantitative measurement of local elasticity of SiOx film by atomic force acoustic microscopy

In this paper the elastic properties of SiOx film are investigated quantitatively for local fixed point and qualitatively for overall area by atomic force acoustic microscopy (AFAM) in which the sample is vibrated at the ultrasonic frequency while the sample surface is touched and scanned with the tip contacting the sample respectively for fixed point and continuous measurements. The SiOx films on the silicon wafers are prepared by the plasma enhanced chemical vapour deposition (PECVD). The local contact stiffness of the tip-SiOx film is calculated from the contact resonance spectrum measured with the atomic force acoustic microscopy. Using the reference approach, indentation modulus of SiOx film for fixed point is obtained. The images of cantilever amplitude are also visualized and analysed when the SiOx surface is excited at a fixed frequency. The results show that the acoustic amplitude images can reflect the elastic properties of the sample.

Phase noise induced due to amplitude fluctuations in dynamic force microscopy

In dynamic force microscopy, the force sensor is driven on its resonance frequency and the amplitude of the cantilever is sustained at a constant value. The amplitude typically ranges between 0.1 and 30 nm. If a large amplitude is set, the cantilever tip senses both long-range and short-range interaction forces provided that the tip is close to the sample surface. The short-range interactions are decisive for the atomic contrast in atomic force microscopy (AFM) images. They can be separated from the long-range interactions by setting an amplitude which encompasses the typical range of the interaction force, i.e., the subangstrom regime for van der Waals contribution. It is distinctive for cantilevers operated at small driving amplitudes that the cantilever deflection can be considered as a sinusoidal signal superimposed with a quasimonochromatic random signal originating from fluctuations. If one measures experimentally the standard deviation of the phase ${\ensuremath{\sigma}}_{\ensuremath{\varphi}}$ of the signal with respect to a monochromatic reference signal, a universal relationship between the standard deviation of the phase ${\ensuremath{\sigma}}_{\ensuremath{\varphi}}$ and the cantilever amplitude ${x}_{0}$ is found. The smaller the ratio of rms amplitude of the sinusoidal signal and the rms value of random signal is, the larger the phase fluctuations are. Phase fluctuations are of importance for measurements at small amplitudes, since they determine the limit of phase-sensitive measurements or the lateral imaging resolution in the so-called pendulum mode of AFM operation. In this paper we develop a heuristic model, which provides an analytical formula for the probability density of phase noise of a sinusoidal signal superimposed by a quasimonochromatic one with respect to a reference oscillator. The variance of the phase noise can be deduced from the distribution functions. The suggested model is verified experimentally and is compared with theoretical predictions. The amplitude-dependent phase fluctuations are a powerful tool to determine the spring constant of the beam or to calibrate its oscillation amplitude.

Adhesion and friction of a multiwalled carbon nanotube sliding against single-walled carbon nanotube

The adhesion and friction at crossed nanotube junctions were investigated in ambient by using an atomic force microscope (AFM) in tapping mode. A multiwalled carbon nanotube (MWNT) tip attached to a conventional AFM probe was scanned across a single-walled carbon nanotube (SWNT) suspended over a $2\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-wide trench. The interaction between nanotubes was found to critically depend on the morphology of the MWNT tip, which was determined from force-distance curves and scans performed against hard trench surface. The interaction between nanotubes caused the attenuation of vibrational amplitude of AFM cantilever, from which the frictional force between nanotubes was obtained by analyzing the dissipated vibrational power of cantilever. The adhesive force between nanotubes was measured from the vertical cantilever deflection when the MWNT tip end detached from the shell of the SWNT. From the friction and adhesion data, an experimental value of coefficient of friction of $0.006\ifmmode\pm\else\textpm\fi{}0.003$ is obtained for the sliding between nanotubes, which is comparable to the reported value of graphite on nanoscale. The shear strength between nanotubes is derived to be $4\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\mathrm{MPa}$ by using a continuum model, which is in accordance with the value of $2\phantom{\rule{0.3em}{0ex}}\mathrm{MPa}$ reported for the sliding of MWNT on graphite in ambient. It is nearly 2 orders of magnitude larger than the interlayer shear strength of $0.05\phantom{\rule{0.3em}{0ex}}\mathrm{MPa}$ reported for MWNT in vacuum. We attribute the difference between the intertube and the interlayer frictions to the presence of water at the nanotube-nanotube interface in ambient.

Tapping mode SPM local oxidation nanolithography with sub-10 nm resolution

Tapping mode SPM local oxidation nanolithography with sub-10 nm resolution is investigated by optimizing the applied bias voltage (V), scanning speed (S) and the oscillation amplitude of the cantilever (A). We fabricated Si oxide wires with an average width of 9.8 nm (V = 17.5 V, S = 250 nm/s, A = 292 nm). In SPM local oxidation with tapping mode operation, it is possible to decrease the size of the water meniscus by enhancing the oscillation amplitude of cantilever. Hence, it seems that the water meniscus with sub-10 nm dimensions could be formed by precisely optimizing the oxidation conditions. Moreover, we quantitatively explain the size (width and height) of Si oxide wires with a model based on the oxidation ratio, which is defined as the oxidation time divided by the period of the cantilever oscillation. The model allows us to understand the mechanism of local oxidation in tapping mode operation with amplitude modulation. The results imply that the sub-10 nm resolution could be achieved using tapping mode SPM local oxidation technique with the optimization of the cantilever dynamics.

Dynamic proportional-integral-differential controller for high-speed atomic force microscopy

In tapping mode atomic force microscopy, the cantilever tip intermittently taps the sample as the tip scans over the surface. This mode is suitable for imaging fragile samples such as biological macromolecules, because vertical oscillation of the cantilever reduces lateral forces between the tip and sample. However, the tapping force (vertical force) is not necessarily weak enough for delicate samples, particularly for biomolecular systems containing weak inter- or intramolecular interactions. Light tapping requires an amplitude set point (i.e., a constant cantilever amplitude to be maintained during scanning) to be set very close to its free oscillation amplitude. However, this requirement does not reconcile with fast scans, because, with such a set point, the tip may easily be removed from the surface completely. This article presents two devices to overcome this difficulty; a new feedback controller (named as “dynamic proportional-integral-differential controller”) and a compensator for drift in the cantilever-excitation efficiency. Together with other devices optimized for fast scan, these devices enable high-speed imaging of fragile samples.