Resonant Microcantilever Research Articles

Exploiting NiTi shape memory alloy films in design of tunable high frequency microcantilever resonators

Shape memory alloy (SMA) films are very attractive materials for microactuators because of their high energy density. However, all currently developed SMA actuators utilize martensitic transformation activated by periodically generated heating and cooling; therefore, they have a slow actuation speed, just a few Hz, which restricts their use in most of the nanotechnology applications such as high frequency microcantilever based physical and chemical sensors, atomic force microscopes, or RF filters. Here, we design tunable high frequency SMA microcantilevers for nanotechnology applications. They consist of a phase transforming NiTi SMA film sputtered on the common elastic substrate material; in our case, it is a single-crystal silicon. The reversible tuning of microcantilever resonant frequencies is then realized by intentionally changing the Young's modulus and the interlayer stress of the NiTi film by temperature, while the elastic substrate guarantees the high frequency actuation (up to hundreds of kHz) of the microcantilever. The experimental results qualitatively agree with predictions obtained from the dedicated model based on the continuum mechanics theory and a phase characteristic of NiTi. The present design of SMA microcantilevers expands the capability of current micro-/nanomechanical resonators by enabling tunability of several consecutive resonant frequencies.

Revealing humidity-enhanced NH3 sensing effect by using resonant microcantilever

High performance NH3 sensor is of great importance in various application fields such as environmental protection and early diagnosis of stomach cancer. Herein, carboxyl group functionalized mesoporous silica nanoparticles (C-MSNs) with ultrahigh specific surface area are developed as high performance mass-type sensing material for trace-level NH3 detection. By using inkjet printing technology, C-MSNs material is precisely loaded on our lab-made integrated resonant microcantilever to construct a mass-type gas sensor. Based on the specific acid-base interaction between Brønsted acidic C-MSNs material and basic NH3 molecules, our sensor exhibits satisfactory NH3 sensing performance. The experimentally observed detection limit of our sensor reaches parts per billion (ppb) level. Exposed to NH3 with identical concentration, our sensor outputs a higher response in wet air than that of in dry atmosphere. In real air, hydrate NH3 molecule (i.e. NH3·xH2O) has a larger molecular weight than anhydrous NH3 in absolute dry experimental atmosphere. Therefore, our gravimetric sensor exhibits a higher response in real air. In order to in-depth elucidate the humidity-enhanced sensing effect, the micro-gravimetric sensing data obtained in wet air and in dry experimental environment are compared together. Based on our quantitatively measurement data, the molecular formula of hydrate NH3·xH2O existing in wet air (with 50–80% relative humidity) can be obtained as NH3·2∼2.4H2O.

Metal organic framework of MOF-5 with hierarchical nanopores as micro-gravimetric sensing material for aniline detection

Aromatic amine such as aniline is one kind of carcinogenic substances that needs to be detected at low concentration. To sense trace level aniline, high performance sensing material is of great importance. Herein, metal organic framework of Zn4O(1,4-benzenedicarboxylate)3 (commonly abbreviated as MOF-5) with abundant hierarchical nanopores is firstly employed as mass-type sensing material for low concentration aniline detection. By using one typical micro-gravimetric transducer of resonant microcantilever, the aniline-adsorbing induced mass-addition of MOF-5 is transformed to the detectible sensing signal of frequency shift. Based on resonant microcantilever with mass resolution of 1.5pg/Hz, the fabricated sensor exhibits good sensitivity for aniline detection. The limit of detection is better than 1.4ppm, and the selectivity is satisfactory to nine kinds of common interfering gases. The three-cycle repeatability of the sensor is also investigated with a relative standard deviation (RSD) of 4%. After 20days, the sensor only shows a negligible response degradation which represents a good reproducibility. Materials Studio simulation results manifest that 1,4-benzenedicarboxylic ligand in MOF-5 crystals is the preferential site for aniline molecules adsorbing.

Microcantilever resonator arrays for immunodetection of β-lactoglobulin milk allergen

The incidence of allergic disease is globally increasing so much that food allergy is actually considered as one of the main diseases of civilization, as well as among the major costs for healthcare worldwide. In such a scenario, the recent legislations introduced from European Union to protect consumers drastically drive the need for rapid, sensitive, and robust techniques to detect allergens within foodstuffs.We here report on an innovative immunorecognition method for β-lactoglobulin milk allergen detection, based on microcantilever resonator arrays, a promising class of biosensors. An original sandwich assay that uses the same polyclonal antibody as capture and secondary immunorecognition agent was proposed to overcome the low affinity of the simple direct method. The developed immunoassay showed better Limit Of Detection (LOD) and Limit Of Quantification (LOQ) than commercial ELISA plates, even after an aging of four months. To our knowledge, this work represents the first example in the literature of successfully immunodetection of milk allergens in low concentrations by microcantilever resonator arrays, thus opening new perspectives on alternative diagnostic tools for milk allergens screening tests.

A Thermoelastic Damping Model for the Cone Microcantilever Resonator with Circular Cross-section

Microbeams with variable cross-section have been applied in Microelectromechanical Systems (MEMS) resonators. Quality factor (Q-factor) is an important factor evaluating the performance of MEMS resonators, and high Q-factor stands for the excellent performance. Thermoelastic damping (TED), which has been verified as a fundamental energy lost mechanism for microresonators, determines the upper limit of Q-factor. TED can be calculated by the Zener’s model and Lifshits and Roukes (LR) model. However, for microbeam resonators with variable cross-sections, these two models become invalid in some cases. In this work, we derived the TED model for cone microcantilever with circular cross-section that is a representative non-uniform microbeam. The comparison of results obtained by the present model and Finite Element Method (FEM) model proves that the present model is valid for predicting TED value for cone microcantilever with circular cross-section. The results suggest that the first-order natural frequencies and TED values of cone microcantilever are larger than those of uniform microbeam for large aspect ratios (l/r0). In addition, the Debye peak value of a uniform microcantilever is equal to 0.5ΔE, while that of cone microcantilever is about 0.438ΔE.

Development of Diamond and Silicon MEMS Sensor Arrays with Integrated Readout for Vapor Detection.

This paper reports on the development of an autonomous instrument based on an array of eight resonant microcantilevers for vapor detection. The fabricated sensors are label-free devices, allowing chemical and biological functionalization. In this work, sensors based on an array of silicon and synthetic diamond microcantilevers are sensitized with polymeric films for the detection of analytes. The main advantage of the proposed system is that sensors can be easily changed for another application or for cleaning since the developed gas cell presents removable electrical connections. We report the successful application of our electronic nose approach to detect 12 volatile organic compounds. Moreover, the response pattern of the cantilever arrays is interpreted via principal component analysis (PCA) techniques in order to identify samples.

Active MEMS metamaterials for THz bandwidth control

We experimentally demonstrate a microelectromechanical system (MEMS) based metamaterial with actively tunable resonance bandwidth characteristics, operating in the terahertz (THz) spectral region. The broadband resonance characteristic feature of the MEMS metamaterial is achieved by integrating sixteen microcantilever resonators of identical lengths but with continuously varying release lengths, to form a supercell. The MEMS metamaterial showed broadband resonance characteristics with a full width half maximum (FWHM) value of 175 GHz for resonators with a metal thickness of 900 nm and was further improved to 225 GHz by reducing the metal thickness to 500 nm. The FWHM resonance bandwidth of the MEMS metamaterial was actively switched to 90 GHz by electrostatically controlling the out-of-plane release height of the constituent microcantilever resonators. Furthermore, the electrically controlled resonance bandwidth allows for the active phase engineering with relatively constant intensity at a given frequency based on the reconfiguration state of the MEMS metamaterial. This enables a pathway for the realization of actively controlled transmission or reflection based on dynamically programmable THz metamaterials.

Density measurement sensitivity of micro-cantilevers influenced by shape dimensions and operation modes

The coupled fluid-solid simulations have been developed to analyze the density measurement sensitivity (DMS) of resonant micro-cantilevers with different shapes, dimensions and operation modes. The analytical formulas have been established to illustrate the relationship of resonant frequency shifts and densities of working fluids. The coupled fluid-solid simulation analyses and experimental results have been used to study the effects of micro-cantilevers with different dimensions on the DMS under bending and torsion modes. The influences of micro-cantilevers with different shapes on the DMS have been also discussed and analyzed. It is concluded that the length and free end width of micro-cantilever as well as operation mode are the key factors affecting the DMS. In addition, the proposed coupled fluid-solid simulation method is an important instruction in the aspect of micro-cantilever design. At the last, the resonant frequency stability and resolution of sensor were analyzed to better understand the sensor’s performance.

High-Throughput Characterization of Microcantilever Resonator Arrays for Low-Concentration Detection of Small Molecules

Microcantilever-based biosensors have shown the ability of highly sensitive label-free detection by allowing the transduction of a target mass into a resonant frequency shift. Even if they have been widely adopted in the last years as high sensitive mass detectors, precision and specificity of such tools are often inadequate. A new platform able to precisely characterize in dynamic mode several of these micromechanical resonators is here presented. Consequently, to the examination of the main parameters involved in a measurement, repeatability and reproducibility of the automated cantilever-based system were estimated. The reported analyses demonstrated that the uncertainty of the system could be reduced to a standard deviation of 6.5 × 10 -6 (parts per million). Thanks to its fine precision, the here-proposed sensing platform was able to detect aflatoxins in naturally contaminated nuts at concentrations as low as 40 pg/mL, nearly two orders of magnitude more sensitive than previous attempts reported in the literature with similar devices.

Mass and stiffness spectrometry of nanoparticles and whole intact bacteria by multimode nanomechanical resonators.

The identification of species is a fundamental problem in analytical chemistry and biology. Mass spectrometers identify species by their molecular mass with extremely high sensitivity (<10−24 g). However, its application is usually limited to light analytes (<10−19 g). Here we demonstrate that by using nanomechanical resonators, heavier analytes can be identified by their mass and stiffness. The method is demonstrated with spherical gold nanoparticles and whole intact E. coli bacteria delivered by electrospray ionization to microcantilever resonators placed in low vacuum at 0.1 torr. We develop a theoretical procedure for obtaining the mass, position and stiffness of the analytes arriving the resonator from the adsorption-induced eigenfrequency jumps. These results demonstrate the enormous potential of this technology for identification of large biological complexes near their native conformation, a goal that is beyond the capabilities of conventional mass spectrometers.

Microgravimetric Analysis Method for Activation-Energy Extraction from Trace-Amount Molecule Adsorption.

Activation-energy (Ea) value for trace-amount adsorption of gas molecules on material is rapidly and inexpensively obtained, for the first time, from a microgravimetric analysis experiment. With the material loaded, a resonant microcantilever is used to record in real time the adsorption process at two temperatures. The kinetic parameter Ea is thereby extracted by solving the Arrhenius equation. As an example, two CO2 capture nanomaterials are examined by the Ea extracting method for evaluation/optimization and, thereby, demonstrating the applicability of the microgravimetric analysis method. The achievement helps to solve the absence in rapid quantitative characterization of sorption kinetics and opens a new route to investigate molecule adsorption processes and materials.

Mass sensing of multiple particles adsorbed to microcantilever resonators

Accurate prediction of resonance frequency shift due to binding of a discrete cell to a microcantilever resonator was achieved, in closed form, by modifying the Dunkerley method. The method was modified by introducing a position-dependent parameter that is independent of particle mass up to 10 % of beam mass. The method was extended to any number of particles attached to the cantilever at any arbitrary locations, and was validated by comparison with experiments. The analysis shows that the resonance frequency shift due to multiple particles is the same as the shift due to an Equivalent Uniformly Distributed Mass, added to the beam, whose magnitude is a function of particle(s) mass and location. The analysis also shows that there is no unique correlation between the resonance shift and either adsorbed cell number or the so-called "effective cell mass". The latter variable is a linear weighting of cell mass according to its location on the cantilever. The use of the modified Dunkerley solution for mass sensing of equal and unequal multiple masses was demonstrated.

Automated high-throughput viscosity and density sensor using nanomechanical resonators

Most methods used to determine the viscosity and mass density of liquids have two major drawbacks: relatively high sample consumption (∼milliliters) and long measurement time (∼minutes). Resonant nanomechanical cantilevers promise to overcome these limitations. Although sample consumption has already been significantly reduced, the time resolution was rarely addressed to date. We present a method to decrease the time and user interaction required for such measurements. It features (i) a droplet-generating automatic sampler using fluorinated oil to separate microliter sample plugs, (ii) a PDMS-based microfluidic measurement cell containing the resonant microcantilever sensors driven by photothermal excitation, (iii) dual phase-locked loop frequency tracking of a higher-mode resonance to achieve millisecond time resolution, and (iv) signal processing to extract the resonance parameters, namely the eigenfrequency and quality factor. The principle was validated by screening series of 3μL droplets of glycerol solutions separated by fluorinated oil at a rate of ∼6s per sample. An analytical hydrodynamic model (Van Eysden and Sader, 2007 [6]) and a reduced order model (Heinisch et al., 2014 [16]) were employed to calculate the viscosity and mass density of the sample liquids in a viscosity range of 1–10.5mPas and a density range of 998–1154kgm−3.

High-Temperature Operation of Electrostatically-Excited Single-Crystalline 4H-SiC Microcantilever Resonators

We fabricated electrostatically-excited single-crystalline 4H-SiC microcantilever resonators with various thicknesses and lengths. Their resonant characteristics were investigated from room temperature (RT) up to 600°C. The resonant frequency of the cantilevers decreased with increasing temperature. From the results, the temperature dependence of Young’s modulus of single-crystalline 4H-SiC was obtained, i.e., 3% decrement with increasing temperature from RT to 600°C. The cantilevers with different thicknesses showed different temperature dependences of the quality factor. A 2-μm-thick cantilever exhibited a high quality factor (Q) (250,000) at RT and the Q decreased to 6,000 at 600°C, which can be explained by thermoelastic damping. On the other hand, a Q of a 0.45-μm-thick cantilever was still high (50,000) even at 600°C.

Hyper-branch sensing polymer batch self-assembled on resonant micro-cantilevers with a coupling-reaction route

In order to develop a volume fabrication route for chemical sensors, hydrogen-bond acidic hyper-branched polymer is synthesized and directly self-assembled in-batch onto MEMS resonant micro-cantilevers as sensing layer. The batch self-assembly is via a facile coupling reaction between the SH group in the self-assembled monolayer (SAM) and one OH group in the hyper-branched polymer. During the self-assembly process of the hyper-branched polymer, the polyurethane-industry used isophorone diisocyanate (IPDI) is employed as the key coupling reagent, since the two NCO coupling groups in IPDI feature different reactivity. The NCO group with higher reactivity is firstly reacted with the SH group pre-grown at the cantilever surface. Then, another NCO group with lower reactivity reacts with one OH group in the hyper-branched polymer. In this way the hydrogen-bond acidic hyper-branch polymer can be batch grafted onto a run of micro-cantilevers for uniform sensing to targeted gas. Through this route, the resonant cantilever gas sensors can be batch produced for uniform detection of trace organophosphates (OPs). Based on the specific interaction between the OH sensing group and the PO group in OP, the targeted molecules can be captured by the hyper-branched sensing polymer, and the mass addition induced frequency shift of the resonant cantilever is output as sensing signal. Sensing experiment is implemented for the sensors taken from one fabrication batch, resulting in satisfactory consistency in sensing performance. Taking 5 sensors as example, the deviation of the sensing response to 2ppm dimethyl methylphosphonate (DMMP) is less than 1%. Besides, the sensor shows good repeatability/selectivity and good linear response to various concentrations (300ppb to 1.5ppm) of DMMP.

Vertical silicon nanowire array‐patterned microcantilever resonators for enhanced detection of cigarette smoke aerosols

The fabrication and use of silicon nanowire (SiNW) array-patterned microcantilever sensors for enhancing aerosol mass detection are described. Surface modification of the cantilever is performed selectively by combining the processes of nanoimprint lithography, photolithography and inductively coupled plasma cryogenic reactive ion etching. Cylindrical wire structures of 300 nm diameter with aspect ratios of 3-7 can be realised for the current SiNWs, which can be altered depending on the nanoimprint stamp size and etching recipe. Owing to the rise in the collection surface area of the sensor provided by vertical SiNWs, an increase of aerosol sampling efficiency can be obtained during cigarette smoke exposure, which is a factor of 1.5 higher than that of a corresponding plain cantilever. This proposed structure is intended to be used as a sensor module of a personal aerosol mass detector.

A Silicon Resonant Micro-Cantilever Biosensor with Closed-Loop Self-Excitation System for Biomacromolecular Detection

A silicon resonant micro-cantilever biosensor was introduced to detect biomacromolecular based on the relationship between the cantilever resonant frequency and the cantilever equivalent mass. A closed-loop self-excitation system was designed to acquire the resonant frequency of micro-cantilever. Two groups of resonant micro-cantilever sensors with different resonant frequencies of 18.192 kHz and 17.688 kHz respectively were tested. The result showed that the detection system can automatically search the resonant frequency of micro-cantilever and locked quickly. To demonstrate the feasibility of this approach, human immunoglobulin G(IgG) as model target biomacromolecular was employed, different concentration of IgG was detected by the resonant micro-cantilever sensors, the mass effect of micro-cantilever was adept and the micro-cantilever was drive by closed-loop circuit. The linearity of micro-cantilever biosensor was very well and the experimental result of sensitivity of micro-cantilever biosensor was about 6.6×106. All the results showed that sensitivity of the presented immunoassay significantly increased by one-order of magnitude and offered great application promises in providing a sensitive, specific, and potent method for real-time detection of biological detection.

Carboxyl functionalized gold nanoparticles in situ grown on reduced graphene oxide for micro-gravimetric ammonia sensing

Here, we present an ammonia (NH3) sensor where carboxyl (COOH) functionalized gold nanoparticles (Au-NPs)/reduced graphene oxide (rGO) hybrid film was developed as micro-gravimetric sensing material. With the help of olefin reducing group in oleylamine solvent, gold precursor of HAuCl4 was directly reduced to Au-NPs on the surface of rGO sheets and the Au-NPs was firmly adsorbed by the rGO sheets through Van-der-Walls-force. Therefore, rGO decorated with Au-NPs (i.e., Au-NPs/rGO hybrid) were prepared. After the removal of oleylamine, the rGO sheets served as nano-shelves to support the Au-NPs, and thereby preventing Au-NPs from aggregating. The rGO shelved Au-NPs was dispersed well under ultrasonic in some conventional solvents like water or ethanol. After drying in air, the obtained composite formed into three-dimensional (3D) hierarchical porous-layered nanostructures, providing effective surface areas for NH3 molecules adsorbing and micro-gravimetric sensing. Thereafter, mercaptosuccinic acid (MSA, bearing two -COOH groups) was self-assembled onto the Au-NPs to form NH3-specific micro-gravimetric sensing material based on the base–acid interaction. Moreover, due to the hydrophobic characteristic of rGO with only a few oxygen-containing group residues, which was prepared by using thermal expansion method under inert atmosphere, the resonant microcantilever with -COOH functionalized Au-NPs/rGO hybrid as sensing material facilitates negligible interference from environmental humidity change.

Estimating Damping in Microresonators by Measuring Thermomechanical Noise Using Laser Doppler Vibrometry

The fluctuation-dissipation theorem establishes the fundamental links between thermomechanical noise and damping. In this paper, we bridge the gap between theory and practice by developing protocols for estimating dissipation in low-loss microresonators by measuring thermomechanical noise using laser Doppler vibrometry. The measurement does not require external actuation of the device and damping can be estimated without relying upon knowledge of material properties, device dimensions, or structural stiffness. The power spectral density of velocity and displacement noise is computed using a direct method that avoids segmenting the measurements in the time domain, thereby avoiding any bias in the estimation of the quality factor. We demonstrate the implementation of the protocol by measuring damping at room temperature and low pressure in four silicon-based microcantilever resonators with natural frequencies ranging from 17.6 to 26.7 kHz and quality factors ranging from $2\times 10^{4}$ to $2\times 10^{5}$ . The accuracy of noise-based estimates is evaluated by comparison with values of the log decrement measured under free decay. $\hfill{[2013\hbox{--}0127]}$

Gas chemical sensitivity of a CMOS MEMS cantilever functionalized via evaporation driven assembly

This work demonstrates an electrostatically actuated resonant microcantilever fabricated in a complementary metal oxide semiconductor process and functionalized with a chemically sorbent polymer layer for the detection of volatile organic compounds. Deposition of the chemically sorbent layer is controlled through evaporation-driven assembly. Analytical and finite element analysis models of the deposited polymer layer on the microcantilever resonant frequency and mass sensitivity are presented. Fabrication of the chemical sensor, including a description of polymer deposition through evaporation-driven assembly within a capillary, is detailed. The completely functionalized resonator demonstrates a limit of detection of 1.6 ppm for toluene. An optimal polymer sensitive layer deposition of 42% of the total beam length is measured from frequency instability and sensitivity tests.