Microcantilever Sensors Research Articles

Fabrication of SiO$_{2}$ Microcantilever Using Isotropic Etching With ICP

This paper reports a new design and microfabrication process for high sensing guard-armed silicon dioxide (SiO2 ) microcantilever sensor, which can be widely used in chemical, environmental and biomedical applications. One sensor platform consists of two SiO2 cantilever beams as the sensing and reference elements, two connecting wings, and three guard arms. The guard arms prevent damage to the cantilever beam from collision. To efficiently release the SiO2 cantilevers from the silicon substrate, an isotropic etch method using inductively coupled plasma (ICP) was developed. The isotropic etching with ICP system provides an advantage in good profile control and high etching rate than wet isotropic etching or conventional RIE (reactive ion etching); however, it has not been gained many attentions. In this work, the effects of chamber pressure, plasma source power, substrate power, SF6 flow rate relating with Si etching rate, undercutting rate, and isotropic ratio were investigated and discussed. The optimum isotropic etching process achieved a 9.1 mum/min etch rate, 70% isotropic ratio, and 92% etching uniformity. The SiO2 cantilever sensor was fabricated and the cantilever beam was successfully released using a patterned photoresist layer as an etching mask. This plasma isotropic etching release processing can be also applied to release other SiO2 or metal suspended MEMS structures, such as bridges and membranes, with a fast etch rate and reasonable isotropic ratio.

The Effect of Flow Velocity on Microcantilever-Based Biosensors

ABSTRACTThis work focuses on studying the effect of flow velocity on microcantilever-based biosensor by numerical simulation. The microcantilever sensors used in detecting biomolecules have attractive advantages like cost efficiency, real-time and ability of fabricating in array. Both rectangular and triangular shapes of a general model of microcantilever beam are considered. Several important physical phenomena are obtained. Comparing with the first order Langmuir theory, we have calculated the effect on the reactive rate, produced concentration, the distribution of concentration and deflection in the z axis by solving these physical coupled problem involving flow field, concentration field and chemical reaction on the reaction surface. It is found numerically that the transportation of analyte, reactive rate, the distribution of concentration and deflection in the z axis are all effected by changing the flow velocity. The result has shown that flow velocity is an important factor for this biosensor.

Toward Ultrasmall Mass Detection Using Adaptive Self-Sensing Piezoelectrically Driven Microcantilevers

Over the past decade, microcantilever-based mass sensing has grown to become a significant field of research in the engineering community. The ability of microcantilevers to detect extremely small biochemical particles is being investigated for a number of industrial applications. This paper presents an adaptive self-sensing strategy for ultrasmall tip mass estimation using piezoelectrically actuated microcantilevers. A piezoelectric patch actuator deposited on the cantilever surface actuates the beam through a capacitance bridge mechanism. The same patch is used to measure shifts in the beam natural frequency associated with increase in the mass, which is due to the addition of biochemical particles. The ability to measure frequency shifts due to tip masses as small as 1 fg (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-15</sup> g) is demonstrated through extensive numerical simulations. Uncertainty in the measurement of system parameters makes implementation of the self-sensing bridge network difficult at the microscale. The piezoelectric capacitance is also known to vary with temperature. To overcome these difficulties, a novel adaptive mechanism is presented to dynamically balance the capacitance bridge network. Lyapunov-based stability analysis demonstrates the global stability of the adaptation laws. Simulation results demonstrate the feasibility of this mechanism to perform self-sensing at the microscale. Experimental validation of the adaptation mechanism at the microscale involves a number of technical challenges, and hence, is performed on a macroscale cantilever system. This paper aims to motivate research in the development of a powerful, yet portable frequency shift detection-based microcantilever sensor for use in a variety of biochemical applications, where ultrasmall mass detection is a key requirement.

Effect of Surface Conjugation Chemistry on the Sensitivity of Microcantilever Sensors

Microcantilever sensors are an offshoot of atomic force microscopy and are useful tools for effectively detecting a target biomolecule. The recognition of the target molecule on the biosensor is based on the physical bending of the microcantilever, which is driven by a specific molecular interaction between the target molecule and the sensor surface. In this study, to enhance the sensitivity of the microcantilever sensor, the sensor surface was modified through a surface conjugation method using self-assembled monolayers (SAMs) and heterobifunctional cross-linkers. After the surface modification of the microcantilever sensor, the sensitivity for L-cysteine was recorded. The detection of L-cysteine was influenced by the active site and the molecular size of the cross-linked compound attached onto the surface of the microcantilever.

On the temperature compensation of parallel piezoresistive microcantilevers in CMOS biosensor

Abstract Microcantilever with embedded piezoresistor has been applied to in situ surface stress measurement of biochemical reaction, where the parallel microcantilever by using an active cantilever for biosensing and another reference cantilever for noise cancellation has previously been proposed. This paper shows that the microcantilever measurement is sensitive to the temperature effect induced by the piezoresistor. The two cantilevers of 125 μm × 60 μm × 0.75 μm may have 40 °C temperature difference, 1.65 mV offset voltage, and 0.01 mV/°C temperature drift in 10 V operation because of their different thermal inertia. A parallel microcantilever design is developed for temperature compensation by using a signal conditioning circuit and the stripe pattern immobilized layer. Analyses and experiments show that the performance of parallel microcantilever sensor can be significantly improved.

Measurement of the Mass and Rigidity of Adsorbates on a Microcantilever Sensor.

When microcantilevers are used in the dynamic mode, the resonance shift uponmaterial adsorption depends on the position of the adsorbate along the microcantilever. Wehave previously described that the adsorbate stiffness needs to be considered in addition toits mass in order to correctly interpret the resonance shift. Here we describe a method thatallows obtaining the Young's modulus of the adsorbed bacteria derived from themeasurement of the frequency shift when adsorbates are placed close to the clampingregion. As a model system we have used E. Coli bacteria deposited on the cantileversurface by the ink-jet technique. We demonstrate that the correct information aboutadsorbed mass can be extracted by recording the cantilever profile and its resonanceresponse. Also, the position and extent of adsorbates is determined by recording themicrocantilever profile. We use a theoretical model based on the Euler - Bernouilliequation for a beam with both mass and flexural rigidity local increase due to the depositedmaterial.

Microcantilever sensors with chemically selective coatings of ionic liquids

AIChE JournalVolume 53, Issue 10 p. 2726-2731 Environmental and Energy Engineering Microcantilever sensors with chemically selective coatings of ionic liquids Eunhyea Chung, Eunhyea Chung School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332Search for more papers by this authorNickolay Lavrik, Nickolay Lavrik Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorPanos Datskos, Panos Datskos Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorJoanna Mcfarlane, Joanna Mcfarlane Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorSheng Dai, Sheng Dai Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorCostas Tsouris, Corresponding Author Costas Tsouris tsourisc@ornl.gov School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332; and Oak Ridge National Laboratory, Oak Ridge, TN 37831School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332; and Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this author Eunhyea Chung, Eunhyea Chung School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332Search for more papers by this authorNickolay Lavrik, Nickolay Lavrik Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorPanos Datskos, Panos Datskos Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorJoanna Mcfarlane, Joanna Mcfarlane Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorSheng Dai, Sheng Dai Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this authorCostas Tsouris, Corresponding Author Costas Tsouris tsourisc@ornl.gov School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332; and Oak Ridge National Laboratory, Oak Ridge, TN 37831School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332; and Oak Ridge National Laboratory, Oak Ridge, TN 37831Search for more papers by this author First published: 31 August 2007 https://doi.org/10.1002/aic.11293Citations: 3Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume53, Issue10October 2007Pages 2726-2731 RelatedInformation

Differentially Ligand-Functionalized Microcantilever Arrays for Metal Ion Identification and Sensing

A microcantilever array sensor with cantilevers differentially functionalized with self-assembled monolayers (SAMs) of thiolated ligands is prepared by simultaneous capillary coating. This array is described for the detection of metal ions including Li+, Cs+, Cu2+, Co2+, Fe3+, and Al3+. Binding of the charged metal cations to the surface of the microcantilever sensors produces surface stress that causes bending of the cantilevers that is detected as tip deflection using an array of vertical cavity surface emitting lasers and a position-sensitive detector. Optimization studies of the nanostructured dealloyed surface were performed for SAMs based on their response to Cu2+ cations. Sensor performance experiments demonstrate good sensitivity toward metal ions, with limits of detection as low as 10(-8) molar. A multiplex capillary coating method for cantilever array creation is demonstrated and validated based on surface-enhanced Raman spectra obtained from adjacent cantilevers that were functionalized with different thiolated SAMs. The cantilever array coated with a range of thiolated ligands was exposed to the group of metal ions. The response characteristics of each metal ion show substantial diversity, varying not only in response magnitude, but response kinetics. A pattern recognition algorithm based on a combination of independent component analysis and support vector machines was able to validate that the sensor array response profiles produced enough information content that metal ions could be reliably classified with probabilities as high as 89%.

Polydimethylsiloxane microfluidic system with in-channel structure for integrated electrochemical detector

Abstract The purpose of this work is to integrate a microfluidic system with biochemical sensors. The proposed microfluidic system consisted with micropumps, microvalves, and microchannels can be applied to PCR, CE-ECD, and microcantilever sensors. This microfluidic system has advantages in terms of its ease of fabrication and bonding process, as well as its biocompatibility. A thermopneumatic-actuated micropump with diffusers was fabricated. The optimum pumping rate of approximately 3.0 l/min was obtained with an inlet width of 60 μm at a 3 Hz frequency. In addition, the microvalve accommodates a paraffin chamber that utilizes the large volume expansion associated with the solid-to-liquid phase transition of paraffin. Between the two different valve seat diameters, the 2 mm diameter showed better performance, where the flow rate reached zero when the applied power supply was approximately 300 mW, than the smaller valve seat diameter of 1.5 mm, which required a higher power supply of 350 mW.

Dual-SAM functionalization on integrated cantilevers for specific trace-explosive sensingand non-specific adsorption suppression

Two self-assembled monolayers (SAMs), 6-mercaptonicotinic acid (6-MNA)and hydrophobic heptadecafluorodecyltrimethoxysilane (FAS-17),are used to specifically modify the two surfaces of a piezoresistiveSiO2 cantilever for functionalizations of both specific explosive-sensing improvement andnon-specific molecular-adsorption suppression. With the dual-SAM modification technique,the on-chip-integrated ultra-sensitive microcantilever sensor behaves more sensitively andhas quicker sensing properties to trace trinitrotoluene (TNT) than the previously reportedcantilever functionalized with 4-MBA SAM, as well as being able to significantlysuppress the cross-talk influence from environmental air humidity. Measurementresults show that the high-performance sensor achieves a rapid, reversible andreproducible response to TNT vapour, with a detecting resolution of tens of ppt.

3-mercaptopropyltrimethoxysilane as insulating coating and surface for protein immobilization for piezoelectric microcantilever sensors

We have examined coating (PbMg(13)Nb(23)O(3))(0.63)-(PbTiO(3))(0.37) (PMN-PT)/tin and lead zirconate titanate (PZT)/glass piezoelectric microcantilever sensor (PEMS) with 3-mercaptopropyl-trimethoxysilane (MPS) by a simple solution method to electrically insulate the PEMS for in-water applications. In contrast to earlier methytrimethoxysilane insulation coating, the MPS coating also facilitated receptor immobilization on the sensor surface via bonding of its sulhydryl group to a bifunctional linker, sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate. We showed that a MPS coating of 21 nm in thickness is sufficient to electrically insulate and provide immobilization surface to the PEMS for in-liquid electrical self-excitation and self-sensing. The in-phosphate buffered saline solution resonance spectra were stable with Q values ranging from 41 to 55. The mass detection sensitivities were determined to be 5x10(-11) and 8x10(-12) gHz for the MPS-insulated PZT-glass and PMN-PT/tin PEMSs, respectively.

Chemical Specificity in Nanomechanical Sensors

¶ Corresponding authors Advances in the field of micro/nano-electro-mechanical systems (MEMS and NEMS) now offer unique opportunities in the design of small and ultrasensitive analytical methods. MEMs/NEMs have demonstrated their unique advantages when they are combined with chemistry and biology, including fast, real-time responses. In addition, MEMs and NEMS are small enough to be integrated into other devices. One of the most promising MEMs is microcantilevers, which have been proven to be an outstanding transducer for chemical and biological sensors. This review summarizes the receptors and immobilization approaches reported for nanomechanical sensors and interpret the mechanism and dynamic relationship of recognition induced nanomechanical motions. Since the three pioneer papers (1-3) published in 1994, the micro/nanocantilever sensor technology had boomed and become a promising sensor technology. Microcantilever sensors have several advantages over many other sensor technologies, including faster response time, lower cost of fabrication, the possibility of sensor arrays with small overall dimensions, the ability to explore microenvironments, and improved portability for field applications. SEM pictures of microcantilevers are shown in Fig. (1). Microcantilevers are miniature diving boards that are micromachined from silicon or other materials. The length of these cantilevers is often in the range of 100-200 microns while the thickness ranges from 200 -1000 nm; Recent advances in micromachining cantilever beams that can detect extremely small forces and mechanical stresses promise to bring about a revolution in the field of chemical, physical, and biological sensor development.

On the micromechanics of micro-cantilever sensors: Property analysis and eigenstrain modeling

Micro-cantilevers can be utilized as sensors primarily due to their low stiffness/high flexibility and high resonance frequency. The cantilever system is therefore very sensitive to small changes of properties that can be detected either as change of deflection, or of resonance frequency. The development of small forces in the near-surface layers results in significant property changes of micro-cantilevers allowing their use for the detection of very small effects, e.g. associated with the adsorption of biological or chemical substances on the cantilever surfaces. While many experiments providing proof of principle deformation have been reported in the literature, quantitative analysis of the cantilever transduction effect requires precise characterization of the device deflection in response to known forces, i.e. detector calibration. The present paper addresses two aspects of this issue: property evaluation of micro-cantilever components, particularly the coating layer, and the use of analytical and numerical models of cantilever deformation using the concept of eigenstrain, a term that is used in residual stress theory to describe inelastic deformation. The analytical model proposed here accounts for the presence of surface tension and thermal mismatch effects, and predicts the resulting cantilever curvature. The numerical model presented is developed within the framework of finite element analysis, and allows the prediction of effects of cantilever attachment to the chip on complete cantilever deflection. Comparisons of model predictions with the experimental data on cantilever deflection due to changes in temperature obtained using optical interferometry show good agreement.

Enhanced mass sensitivity of stress-free, silicon nanowire-grown microcantilever sensors

A thin catalytic layer of nickel was evaporated onto one side of silicon microcantilevers and amorphous silicon nanowires were synthesized on the nickel surface. When nanowire-grown cantilevers were exposed to mercaptohexanol vapor, their mass sensitivity was almost two orders of magnitude greater than that of the corresponding plain cantilever due to the increase in surface area afforded by the nanowires, whereas adsorption of mercaptohexanol induced negligible deflection of the nanowire-grown cantilevers. This indicates that the gold-coated nanowire-grown cantilever can be used as a sensitive, stress-free sensor whose spring constant is not affected by the adsorption of alkanethiols.

In situ, in-liquid, all-electrical detection of Salmonella typhimurium using lead titanate zirconate/gold-coated glass cantilevers at any dipping depth

Most biosensing techniques are indirect, slow, and require labeling. Even though silicon-based microcantilever sensors are sensitive and label-free, they are not suitable for in-liquid detection. More recently lead zirconate titanate (PZT) thin-film-based microcantilevers are shown to be sensitive and in situ. However, they require microfabrication and must be electrically insulated. In this study, we show that highly sensitive, in situ, Salmonella typhimurium detection can be achieved at 90% relative humidity using a lead zirconate titanate (PZT)/gold-coated glass cantilever 0.7mm long with a non-piezoelectric 2.7mm long gold-coated glass tip by partially dipping the gold-coated glass tip in the suspension at any depth without electrically insulating the PZT. In particular, we showed that at 90% relative humidity and with a dipping depth larger than 0.8mm the PZT/gold-coated glass cantilever showed virtually no background resonance frequency up-shift due to water evaporation and exhibited a mass detection sensitivity of Δm/Δf=−5×10−11g/Hz. The concentration sensitivities of this PZT/gold-coated glass cantilever were 1×103 and 500cells/ml in 2ml of liquid with a 1 and 1.5mm dipping depth, respectively, both more than two orders of magnitude lower than the infectious dose and more than one order of magnitude lower than the detection limit of a commercial Raptor sensor.

Detection of Cd(II) using antibody-modified microcantilever sensors

This work demonstrated the feasibility of detecting divalent Cd(II) ions using antibody-modified microcantilever (MCL) sensors. Different surface modification methods were compared and multilayer approach was found superior than others for MCL surface modifications for antibody-based Cd(II) sensor development. When the Cd(II)–EDTA complex sample is injected into the fluid cell where the MCL is held, the MCL bends upon the recognition of the Cd(II) complex by the antibody on the surface of the MCL. Control experiments showed that complex that does not contain Cd(II) did not cause any bending of the MCL. The detection limit of the sensor was approximately 10 −9 M. The reaction rate analysis indicated that Langmuir adsorption model is appropriate to describe the absorption of Cd(II)–EDTA–BSA on the antibody-covered MCL surface.

Role of the gold film nanostructure on the nanomechanical response of microcantilever sensors

In this study, we have determined the relationship between the nanostructure of the gold film deposited on microcantilevers and the sensitivity and reproducibility of their static response to molecular adsorption. In order to tune the properties of the gold film, gold was deposited at different rates and thicknesses. The cantilever response to molecular adsorption was characterized by exposure of the cantilevers to mercaptohexanol in water. The morphology of the gold surface was characterized by atomic force microscopy, and the residual stress induced in the cantilevers was characterized by a profilometry technique based on the optical beam deflection method. We have found that the discontinuous morphology of the gold film for small thicknesses and low deposition rates gives rise to large values of residual tensile stress due to the formation of grain boundaries at the expense of strain energy. These cantilevers exhibit the highest sensitivity and reproducibility to molecular adsorption. However, larger thicknesses and higher deposition rates produce the coalescence of gold nanoislands via atom diffusion. This is characterized by a large relative decrease (increase) of the tensile (compressive) stress. These cantilevers exhibit small sensitivity and low reproducibility to molecular adsorption. We conclude that the control of the gold coating process is critical for the reliability of the measurements with nanomechanical sensors.

Human hydration level monitoring using embedded piezoresistive microcantilever sensors

Embedded piezoresistive microcantilever (EPM) sensors were used to measure osmolality changes in both saliva mimic solutions and true human saliva. Osmolality changes in human saliva or urine may prove to be reliable, simple, and easy to measure markers for tracking human hydration levels. EPM sensors used in these experiments show good response to osmolality changes in both NaCl-based saliva mimic solutions and to human saliva. The addition of zero-point offset correction to EPM sensors allows for tracking of saliva osmolality changes with high accuracy. Also, the same EPM sensors exhibit a large enough range of osmolality response to make them potentially suitable for urine or blood serum osmolality monitoring.

A Model-Based Processor Design for Smart Microsensor Arrays [Applications Corner

In this article, we discuss the design of a smart-physics-based processor for microcantilever sensor arrays. The processor is coupled to a microelectromechanical sensor and estimates the presence of critical materials or chemicals in solution. We first briefly present microcantilever sensors and then discuss the microcantilever sensor array design, which consists of the cantilever physics propagation model, cantilever array measurement model, model-based parameter estimator design, and model-based processor (MBP) design. Finally, we end with experimental results and conclusions

Hydrogel Based Composite Materials for Chemical, Biological and Medical Sensing Applications

AbstractEmbedded piezoresistive microcantilever (EPM) sensors provide a tiny, low-cost, and robust platform for the detection of chemical or biological analytes. New sensing applications become potentially available as the design or synthesis of new sensing materials for EPM instruments are studies. In this study, we report on the detection of hydrogen fluoride gas (HF) in air, and in a medical application, the measurement of human hydration levels. Two sensing materials characterize these applications, thiolated gold nanoparticles in a keratin matrix (HF), and a crosslinked PVA-based hydrogel in the hydration application.