Micro- and nanoelectromechanical systems, including cantilevers and other small scale structures, have been studied for sensor applications. Accurate sensing of gaseous or aqueous environments, chemical vapors, and biomolecules have been demonstrated using a variety of these devices that undergo static deflections or shifts in resonant frequency upon analyte binding. In particular, biological detection of viruses, antigens, DNA, and other proteins is of great interest. While the majority of currently used detection schemes are reliant on biomarkers, such as fluorescent labels, time, effort, and chemical activity could be saved by developing an ultrasensitive method of label-free mass detection. Micro- and nanoscale sensors have been effectively applied as label-free detectors. In the following, we review the technologies and recent developments in the field of micro- and nanoelectromechanical sensors with particular emphasis on their application as biological sensors and recent work towards integrating these sensors in microfluidic systems.

http://cau.ac.kr/~jjang14/BioMEMS/Waggoner_LOC_Cantilever_Sensors_Bio_detection_Review_2007.pdf

Micro- and nanomechanical sensors for environmental, chemical, and biological detection

This article reviews the development of multifrequency force microscopy and examines its application in studies of proteins, the imaging of vibrating nanostructures, measurements of ion diffusion, and subsurface imaging in cells.

/pdf/the-emergence-of-multifrequency-force-microscopy-27841di7vx.pdf

The emergence of multifrequency force microscopy

http://people.bu.edu/parkhs/Papers/eomPR2011.pdf

Nanomechanical resonators and their applications in biological/chemical detection: Nanomechanics principles

Control can enable high-bandwidth nanopositioning needed to increase the operating speed of scanning probe microscopes (SPMs). High-speed SPMs can substantially impact the throughput of a wide range of emerging nanosciences and nanotechnologies. In particular, inversion-based control can find the feedforward input needed to account for the positioning dynamics and, thus, achieve the required precision and bandwidth. This article reviews inversion-based feedforward approaches used for high-speed SPMs such as optimal inversion that accounts for model uncertainty and inversion-based iterative control for repetitive applications. The article establishes connections to other existing methods such as zero-phase-error-tracking feedforward and robust feedforward. Additionally the article reviews the use of feedforward in emerging applications such as SPM-based nanoscale combinatorial-science studies, image-based control for subnanometer-scale studies, and imaging of large soft biosamples with SPMs.

https://faculty.washington.edu/devasia/Research/Papers/2009_Feedforward_review_paper.pdf

A review of feedforward control approaches in nanopositioning for high-speed spm

Multi-harmonic atomic force microscopy can be used to map the local mechanical properties of live cells with better temporal and spatial resolution than has been achieved before.

Mapping nanomechanical properties of live cells using multi-harmonic atomic force microscopy.

The hydrodynamic loading of elastic microcantilevers vibrating in viscous fluids is analyzed computationally using a three-dimensional, finite element fluid-structure interaction model. The quality factors and added mass coefficients of several modes are computed accurately from the transient oscillations of the microcantilever in the fluid. The effects of microcantilever geometry, operation in higher bending modes, and orientation and proximity to a surface are analyzed in detail. The results indicate that in an infinite medium, microcantilever damping arises from localized fluid shear near the edges of the microcantilever. Closer to the surface, however, the damping arises due to a combination of squeeze film effects and viscous shear near the edges. The dependence of these mechanisms on microcantilever geometry and orientation in the proximity of a surface are discussed. The results provide a comprehensive understanding of the hydrodynamic loading of microcantilevers in viscous fluids and are expected to be of immediate interest in atomic force microscopy and microcantilever biosensors.

/pdf/hydrodynamic-loading-of-microcantilevers-vibrating-in-2xeu3uo1lg.pdf

Hydrodynamic loading of microcantilevers vibrating in viscous fluids

A mathematical model is presented to predict the oscillating dynamics of atomic force microscope cantilevers with nanoscale tips tapping on elastic samples in liquid environments. Theoretical simulations and experiments performed in liquids using low stiffness probes on hard and soft samples reveal that, unlike in air, the second flexural mode of the probe is momentarily excited near times of tip-sample contact. The model also predicts closely the tip amplitude and phase of the tip at different set points.

/pdf/dynamics-of-tapping-mode-atomic-force-microscopy-in-liquids-2p74wx7ebn.pdf

Dynamics of tapping mode atomic force microscopy in liquids: Theory and experiments

Atomic Force microscope (AFM) cantilevers commonly used for imaging soft biological samples in liquids experience a momentary excitation of the higher eigenmodes at each tap. This transient response is very sensitive to the local sample elasticity under gentle imaging conditions because the higher eigenmode time period is comparable to the tip-sample contact time. By mapping the momentary excitation response, we demonstrate a new scanning probe spectroscopy capable of resolving with high sensitivity the variations in the elasticity of soft biological materials in liquids.

/pdf/compositional-contrast-of-biological-materials-in-liquids-19laltz74l.pdf

Compositional contrast of biological materials in liquids using the momentary excitation of higher eigenmodes in dynamic atomic force microscopy.

Piezoelectric fans are gaining in popularity as low-power-consumption and low-noise devices for the removal of heat in confined spaces. The performance of piezoelectric fans has been studied by several authors, although primarily at the fundamental resonance mode. In this article the performance of piezoelectric fans operating at the higher resonance modes is studied in detail. Experiments are performed on a number of commercially available piezoelectric fans of varying length. Both finite element modeling and experimental impedance measurements are used to demonstrate that the electromechanical energy conversion (electromechanical coupling factors) in certain modes can be greater than in the first bending mode; however, losses in the piezoceramic are also shown to be higher at those modes. The overall power consumption of the fans is also found to increase with increasing mode number. Detailed flow visualizations are also performed to understand both the transient and steady-state fluid motion around these fans. The results indicate that certain advantages of piezoelectric fan operation at higher resonance modes are offset by increased power consumption and decreased fluid flow

/pdf/piezoelectric-fans-using-higher-flexural-modes-for-44kfw5yvev.pdf

Piezoelectric Fans Using Higher Flexural Modes for Electronics Cooling Applications

Piezoelectrically excited, resonant, elastic beams find wide use as piezoelectric fans, optical choppers, MEMS sensors, and piezoelectric motors. The devices consist of either one piezoelectric ceramic patch (piezopatch) bonded on one side (asymmetric configuration), or of two oppositely poled patches placed symmetrically on either side of a thin, flexible elastic beam (symmetric configuration). Field equations of the coupled structure governing the coupled longitudinal and bending motions of the resonator are derived using linear constitutive equations, slender beam approximations, and Hamilton's principle. Analytical solutions are found to the coupled eigenvalue problem. Eigenvalues and eigenfunctions for the short-circuited and open-circuited configurations are predicted analytically and are found to be in excellent agreement with results from three-dimensional finite element simulations. Electromechanical coupling factors (EMCF) are computed using the analytical and finite element model and optimal resonator geometries are identified for maximal EMCF. The EMCF predictions are also compared with experiments for an asymmetrically configured resonator. The analytical solution provides a convenient tool for the optimal design of such devices.

/pdf/dynamic-response-optimization-of-piezoelectrically-excited-44cerpxueb.pdf

Sudipta Basak

Papers

Hydrodynamic loading of microcantilevers vibrating in viscous fluids

Dynamics of tapping mode atomic force microscopy in liquids: Theory and experiments

Compositional contrast of biological materials in liquids using the momentary excitation of higher eigenmodes in dynamic atomic force microscopy.

Piezoelectric Fans Using Higher Flexural Modes for Electronics Cooling Applications

Dynamic Response Optimization of Piezoelectrically Excited Thin Resonant Beams