Microcantilever System Research Articles

Numerical heat and mass transfer in magnetized Williamson liquid motion over a sensor wall engulfed in a micro-cantilever system: An application to thin-film fluidic cells

Central focus of this numerical analysis is to investigate the influence of magnetic body force and thermal radiation on the time-dependent electrically conducting two-dimensional viscous incompressible boundary layer flow of non-Newtonian Williamson fluid over a microcantilever sensor surface suspended in a squeezed regime numerically. A novel heat source/sink and Soret effects are included in the respective governing equations. The constructed time-dependent nonlinear coupled partial differential equations are solved by using a bobust RK-4 technique. Increasing magnetic number increases the velocity distribution and decreases the temperature and concentration profiles in the flow regime.Enhancing Soret number increases the mass diffusion profile. Increasing magnetic number suppress the skin-friction coefficient. Heat transport rate booted with rising radiation number and Sherwood number decreased with enlarged Schmidt number in the channel regime. Finally, the numerical accuracy of the present similarity solutions and used numerical method is validated with existing results and observed a remarkable agreement.

Mimicking the Tendon Microenvironment to Enhance Skeletal Muscle Adhesion and Longevity in a Functional Microcantilever Platform.

Microcantilever platforms are functional models for studying skeletal muscle force dynamics in vitro. However, the contractile force generated by the myotubes can cause them to detach from the cantilevers, especially during long-term experiments, thus impeding the chronic investigations of skeletal muscles for drug efficacy and toxicity. To improve the integration of myotubes with microcantilevers, we drew inspiration from the elastomeric proteins, elastin and resilin, that are present in the animal and insect worlds, respectively. The spring action of these proteins plays a critical role in force dampening in vivo. In animals, elastin is present in the collagenous matrix of the tendon which is the attachment point of muscles to bones. The tendon microenvironment consists of elastin, collagen, and an aqueous jelly-like mass of proteoglycans. In an attempt to mimic this tendon microenvironment, elastin, collagen, heparan sulfate proteoglycan, and hyaluronic acid were deposited on a positively charged silane substrate. This enabled the long-term survival of mechanically active myotubes on glass and silicon microcantilevers for over 28 days. The skeletal muscle cultures were derived from both primary and induced pluripotent stem cell (iPSC)-derived human skeletal muscles. Both types of myoblasts formed myotubes which survived for five weeks. Primary skeletal muscles and iPSC-derived skeletal muscles also showed a similar trend in fatigue index values. Upon integration with the microcantilever system, the primary muscle and iPSC-derived myotubes were tested successively over a one month period, thus paving the way for long-term chronic experiments on these systems for both drug efficacy and toxicity studies.

On the Sensitivity Analysis of Mode-Localized Sensors Based on Weakly Coupled Resonators

Purpose: This work investigates the mode veering and mode localization behavior of a coupled micro-cantilever system with mass disturbances. A new sensitivity metric is defined based on the difference between the absolute values of amplitude ratios for mass sensing in mode-localized sensors.Methods: Numerical and finite element method (FEM) analyses are conducted to validate the corresponding analytical results for the undamped modal analysis. In addition, the derived sensitivity is also verified by the FEM result of the damped harmonic responses. Finally, an experimental study is conducted to qualitatively validate the theoretical and numerical results.Results: The derived sensitivity shows a good agreement with the numerical and FEM results for the modal analysis and damped harmonic responses. The experimental results show the same trend observed in the theoretical and finite element results. The derived sensitivity possesses a superior linearity in the full disturbance range with high precision. The influence of the damping and coupling factor on the resolution of mass sensing is also unveiled.Conclusions: The superior linearity and effectiveness of the proposed sensitivity metric is confirmed, which has a full scope of application and high precision compared to the conventional sensitivities. The derived sensitivity is proved to be applicable for the damped harmonic response analysis as well. This work also reveals that there is a trade-off between the sensitivity and resolution when selecting the coupling factor.

Double-peak resonant mapping of cellular viscoelasticity in force-clamp detection of atomic force microscope

The mechanical properties of cells are very important to their physiological functions and pathological states, and their variations are also potential indications for early identification of the relevant diseases such as various cancers. With the development of microcantilever sensor, the atomic force microscope (AFM) has become one of the most commonly used tools to detect nanoscale biomolecular mechanical properties. In this contribution, an integral type inhomogeneous viscoelastic moving boundary effect in AFM system is accurately delineated, and a potential conceptual proposal of using the double-peak resonance for microcantilever dynamic system is suggested to detect viscoelasticity of fixed cells. Mathematical models for the quasi-static and dynamic responses of microcantilever system with a viscoelastic moving boundary effect are presented. Laplace transform and its inverse transform, and differential method in the temporal domain and extended differential quadrature method (DQM) in the spatial domain are combined to obtain the relevant analytical solutions for quasi-static response and numerical solutions for dynamical response. Analytical results for quasi-static response agree well with the previous experiments and our simulations by the extended DQM. The results not only reveal that moving boundary conditions and cellular viscoelasticity cannot be ignored for signal extractions in the processes of cellular detection due to their significant influence on interaction force, bending deflection, natural frequency, and mode shape of microcantilever system, but also indicate a double-peak resonance-based method that could be potentially used to identify the transient-, steady-state modulus, and relaxation time of fixed cells.

Simulation and experimental analysis of tip response of tapping mode atomic force microscope

In this study, the vertical deflection responses of tapping mode atomic force microscope (TM-AFM) micro-cantilever tip are obtained by simulation and experiment. The results show that, under the blocking of the sample on one side, the steady-state response of the tip is still a sinusoidal form almost symmetrical about the equilibrium position. Furthermore, from the perspective of energy dissipation of the micro-cantilever system, the phases of two surfaces with different properties are simulated under different background dissipation. The result shows that eliminating partial background dissipation can increase the phase contrast between the two surfaces. These results are of significance for understanding the tip response and phase optimization in TM-AFM.

Theoretical and experimental study of phase optimization of tapping mode atomic force microscope

Phase image in tapping-mode atomic force microscope (TM-AFM) results from various dissipations in a microcantilever system. The phases mainly reflect the tip-sample contact dissipations which allow the nanoscale characteristics to be distinguished from each other. In this work, two factors affecting the phase and phase contrast are analyzed. It is concluded from the theoretical and experimental results that the phases and phase contrasts in the TM-AFM are related to the excitation frequency and energy dissipation of the system. For a two-component blend, it is theoretically and experimentally proven that there exists an optimal excitation frequency for maximizing the phase contrast. Therefore, selecting the optimal excitation frequency can potentially improve the phase contrast results. In addition, only the key dissipation between the tip and sample is found to accurately reflect the sample properties. Meanwhile, the background dissipation can potentially reduce the contrasts of the phase images and even mask or distort the effective information in the phase images. In order to address the aforementioned issues, a self-excited method is adopted in this study in order to eliminate the effects of the background dissipation on the phases. Subsequently, the real phase information of the samples is successfully obtained. It is shown in this study that the eliminating of the background dissipation can effectively improve the phase contrast results and the real phase information of the samples is accurately reflected. These results are of great significance in optimizing the phases of two-component samples and multi-component samples in atomic force microscope.

Microfluidic microcantilever as a sensitive platform to measure evaporation rate of picoliters of ethanol

Resonating microfluidic cantilevers are used for a broad range of biochemical sensing applications where a shift in the resonance frequency is used to detect minute changes in the cantilever mass. These multifunctional microfluidic microcantilevers open up opportunities for new ultrasensitive biochemical sensors wherein the target species in a carrier fluid bind to the inner functionalized walls of microfluidic channel, thereby changing the mass and hence the resonance frequency of the system for detection. In this paper, we develop computational models that predict the change in the resonance frequency as a function of change in mass for this hollow microcantilever system. We present computational models to simulate this process and validate the models using experimental data based on the evaporation of ethenol, a commonly available volatile compound. Specifically, a computational approach is presented in two variants; a one-dimensional structural beam element model, and a three-dimensional finite element model. The numerically predicted increase in the resonance frequencies due to a decrease in ethanol mass correlates well with experimental data. The models enable the determination of proof-of-concept and the rational design of novel resonant-based microfluidic microcantilever systems.

The limit of mass determination with an AFM cantilever-based system

The application of an atomic force microscope (AFM) based microcantilever system for the determination of mass of gold nanoparticles (AuNPs) has been demonstrated. In this system, standard AFM microcantilevers for measurements in vacuum have been employed. The limit of mass determination with our AFM-based system has been determined to be of the order of 10-10 g. The prospects of employing AFM cantilever-based sensors for highly sensitive protein detection in proteomic studies and in diagnostics have been discussed.

Evaluation of Porous Silicon Oxide on Silicon Microcantilevers for Sensitive Detection of Gaseous HF.

Sensitive detection of harmful chemicals in industrial applications is pertinent to safety. In this work, we demonstrate the use of a sensitive silicon microcantilever (MC) system with a porous silicon oxide layer deposited on the active side of the MCs that have been mechanically manipulated to increase sensitivity. Included is the evaluation of porous silicon oxide present on different geometries of MCs and exposed to varying concentrations of hydrogen fluoride in humid air. Profilometry and the signal generated by the stress-induced porous silicon oxide (PSO) coating and bending of the MC were used as methods of evaluation.

Correction: Metal ion binding properties of a bimodal triazolyl-functionalized calix[4]arene on a multi-array microcantilever system. Synthesis, fluorescence and DFT computation studies

Correction for ‘Metal ion binding properties of a bimodal triazolyl-functionalized calix[4]arene on a multi-array microcantilever system. Synthesis, fluorescence and DFT computation studies’ by Abdullah N. Alodhayb et al., RSC Adv., 2016, 6, 4387–4396.

A microcantilever system with slider-crank actuation mechanism

A microcantilever system with new actuation principle is developed for enhancing the range of tip deflection. Differing from conventional springboard-like actuation principle, the proposed microcantilever system is based on a slider-crank mechanism. In this system, out-of-plane deflection of the microcantilever can be translated and amplified from in-plane motion of high-powered thermal actuators, which is located away from cantilever body to ensure both energetic driving force and good thermal isolation. Analytical models of both the microcantilever system and the electrothermal actuator are studied concerning the optimized geometry for desired amplification ratio and balanced force/displacement outputs. The prototype is fabricated by standard lithographic process, and an integrated sharp tip is easily machined by a hybrid wet/dry etching method. The fabricated cantilever is experimentally tested and shows that a 22μm in-plane motion from actuators at an input electrical power of 1026mW can drive the microcantilever to deflect up to 230μm, demonstrating the expected actuation principle. The developed microcantilever system with integrated sharp tip shows the promise to work as a microprobe in the multifunctional analysis instrument.

Post-CMOS compatible high-throughput fabrication of AlN-based piezoelectric microcantilevers

A post-complementary metal oxide semiconductor (CMOS) compatible microfabrication process of piezoelectric cantilevers has been developed. The fabrication process is suitable for standard silicon technology and provides low-cost and high-throughput manufacturing. This work reports design, fabrication and characterization of piezoelectric cantilevers based on aluminum nitride (AlN) thin films synthesized at room temperature. The proposed microcantilever system is a sandwich structure composed of chromium (Cr) electrodes and a sputtered AlN film. The key issue for cantilever fabrication is the growth at room temperature of the AlN layer by reactive sputtering, making possible the innovative compatibility of piezoelectric MEMS devices with CMOS circuits already processed. AlN and Cr have been etched by inductively coupled plasma (ICP) dry etching using a BCl3–Cl2–Ar plasma chemistry. As part of the novelty of the post-CMOS micromachining process presented here, a silicon Si (1 0 0) wafer has been used as substrate as well as the sacrificial layer used to release the microcantilevers. In order to achieve this, the Si surface underneath the structure has been wet etched using an HNA (hydrofluoric acid + nitric acid + acetic acid) based solution. X-ray diffraction (XRD) characterization indicated the high crystalline quality of the AlN film. An atomic force microscope (AFM) has been used to determine the Cr electrode surface roughness. The morphology of the fabricated devices has been studied by scanning electron microscope (SEM). The cantilevers have been piezoelectrically actuated and their out-of-plane vibration modes were detected by vibrometry.

Temperature Changes in Brown Adipocytes Detected with a Bimaterial Microcantilever

Mammalian cells must produce heat to maintain body temperature and support other biological activities. Methods to measure a cell’s thermogenic ability by inserting a thermometer into the cell or measuring the rate of oxygen consumption in a closed vessel can disturb its natural state. Here, we developed a noninvasive system for measuring a cell’s heat production with a bimaterial microcantilever. This method is suitable for investigating the heat-generating properties of cells in their native state, because changes in cell temperature can be measured from the bending of the microcantilever, without damaging the cell and restricting its supply of dissolved oxygen. Thus, we were able to measure increases in cell temperature of <1 K in a small number of murine brown adipocytes (n = 4–7 cells) stimulated with norepinephrine, and observed a slow increase in temperature over several hours. This long-term heat production suggests that, in addition to converting fatty acids into heat energy, brown adipocytes may also adjust protein expression to raise their own temperature, to generate more heat. We expect this bimaterial microcantilever system to prove useful for determining a cell’s state by measuring thermal characteristics.

Developments of Multi-extreme High Field ESR in Kobe

Recent developments of “multi-extreme” high magnetic field electron spin resonance (ESR) in Kobe will be reviewed. Our high magnetic field ESR covers the frequency region between 0.03 and 7 THz and the temperature region between 1.8 and 300 K. With this high magnetic field ESR system we can apply the magnetic field up to 55 T using a Cu-Ag pulsed magnet and a 300 kJ (10 kV) capacitor bank. Under this high magnetic field we can also apply the high pressure up to 1.4 GPa. As we can make the measurement under low temperature, high magnetic field and high pressure simultaneously, we name it as “multi-extreme” ESR. Moreover, in order to gain the sensitivity of our high magnetic field ESR, we have developed a micro-cantilever ESR system using a torque method, which enables the ESR measurement of micrometer size single crystal at low temperature. At the moment we are in the process of extending the magnetic field region of micro-cantilever ESR. Recently we have succeeded in making the measurement up to 369 GHz and the achieved sensitivity is about 1010 spins/G, which is much higher than that using the conventional transmission method. Finally our development of magnetization detected ESR using SQUID magnetometer (SQUID ESR) will be also presented.

Fabrication and characterization of electromagnetically actuated microcantilevers for biochemical sensing, parallel AFM and nanomanipulation

Here we present a microcantilever system with a combination of robust Lorentz force-based electromagnetic actuation and highly sensitive optical beam deflection (OBD) method. We present the microcantilevers' architecture, manufacturing process, and wide characteristics including spring constants, static and dynamic response and a study of coupling between them. Highest measured static electromagnetic and thermal actuation responsivities are 1.82nm/@mAT and 1.47x10^-^4nm/@mA^2 (or 1.34nm/@mW), respectively, while force resolution is 12pN for a 35mN/m microcantilever. During investigations of the Brownian noise of the microcantilevers we have observed anomalous frequency shift caused by static bending. We suggest using this phenomenon to tune micromechanical devices. We propose numerous applications for presented system.

Micromechanical measurement of AChBP binding for label-free drug discovery

A potential binding assay based on binding-driven micromechanical motion is described. Acetylcholine binding protein (AChBP) was used to modify a microcantilever. The modified microcantilever was found to bend on application of the naturally occurring agonist (acetylcholine) or the antagonist (nicotine and d-tubocurarine). Control experiments show that microcantilevers modified without AChBP do not respond to acetylcholine, nicotine, and d-tubocurarine. K(d) values obtained for acetylcholine, nicotine, and d-tubocurarine are similar to those obtained from radio-ligand binding assays. These results suggest that the microcantilever system has potential for use in label free, drug screening applications.

The influence of refractive index change on a micro-cantilever bio/chemical sensor system based on optical lever read-out method

The refractive index of the liquid was speculated to influence the detection signal in a micro-cantilever biosensing system based on optical lever read-out method. In this paper, we present the theoretical analysis of the influence of refractive index change on the detection signal. The results showed that the detection signal of system was greatly impacted by the change of the liquid refractive index as small as 10 −3. By conditioning the experimental parameter such as incidence angle of laser, angle between micro-cantilever and liquid surface, the effect can be effectively eliminated without reducing the detecting sensitivity of the system. The theoretical results were validated by the experiments.

Mathematical analysis on a model for the rectangular cantilever beam

The mechanical model for the rectangular cantilever beam proposed by Zhang et al is solved analytically by the series solution with mathematical properties investigated in detail. The derived series solution is proved convergent, and restrained only by the small deflection presumed by the Euler–Bernoulli beam theorem, and is applicable for calculating the deflection and curvature for any value of the exerted axial stress. The formulae estimating the accuracy of the coefficients and the series solution are developed from Stirling's approximation for the gamma function. The condition on the axial stress is developed, by which the genuinely nonlinear curvature can be approximated by a linear function and the deflection can be calculated from the boundary condition by a cubic polynomial. The additional redundant boundary condition used in Zhang's work is discussed, which should be removed since it fails to fit the model by inducing errors for calculating the deflection and the curvature. The present series solution approach provides formal deflection–stress and curvature–stress relations for the design of a MEMS micro-cantilever system as a bio-detection device. For self-assembly applications, the adsorbing material can be identified by solving the exerted axial stress from the series solution.

Flexural vibrations of microcantilevers coupled with a nanofiber

In this study, the flexural vibrations of a microcantilever system coupled with a nanofiberoffset from the free ends of the cantilevers are explored. Here, for this system, we derive thegeneral expressions for the characteristic equation and sensitivity of vibration modes of amicrocantilever system with a nanofiber wrapped offset from the free ends of thecantilevers. It is shown that each mode has a different sensitivity that depends on thenanofiber stiffness relative to the beam stiffness. We also show how the characteristicequation can be exploited with the knowledge of the resonant frequencies to determine thenanofiber stiffness and its attachment position on the microcantilevers. Plots of nanofiberposition on the cantilevers versus wavenumber are used to show the effect of theposition of the nanofiber on frequency measurements. The results are anticipated toprovide a basic understanding between the vibration modes and the propertiesof the electrospun nanofibers, that may be used to optimize the experiments.

Surface Stress Changes Induced by the Conformational Change of Proteins

A potential binding assay based on conformational-change-induced micromechanical motion is described. Calmodulin was used to modify a microcantilever (MCL) by a self-assembled layer-by-layer approach. The results showed that the modified MCL bent when the proteins changed their conformation upon binding with Ca2+. The cantilever deflection amplitudes were different under different ionic strengths, indicating different degrees of conformational change of the proteins in these conditions. On the contrary, cantilevers modified by proteins, such as hemoglobin and myoglobin, that do not change conformations upon binding with analytes do not cause the cantilever deflection. These results suggest that the conformational changes of proteins may be used to develop cantilever biosensors, and the MCL system has potential for use in label-free, protein-analyte screening applications.